Tooth Components Quiz
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Tooth Components Quiz

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Questions and Answers

What primarily composes the bulk of each tooth?

  • Dentin (correct)
  • Enamel
  • Pulp
  • Cementum

    • Which layer covers the dentin of the crown and is the hardest substance in the body?

  • Enamel (correct)
  • Gingiva
  • Dentin
  • Pulp

    • What is the function of the occlusal surface of a tooth?

  • For crushing, slicing, or chewing food (correct)
  • To absorb nutrients
  • For tooth development
  • To support the jaw

    • What is the primary function of the pulp cavity in a tooth?

    <p>Contains nerve and blood vessels</p> Signup and view all the answers

    What mineral is essential for the formation of enamel?

    <p>Calcium</p> Signup and view all the answers

    What condition is characterized by a shortened frenulum of the tongue?

    <p>Ankyloglossia</p> Signup and view all the answers

    Which of the following components does NOT make up a tooth?

    <p>Lingual frenulum</p> Signup and view all the answers

    Which structure helps to manipulate materials inside the mouth?

    <p>Tongue</p> Signup and view all the answers

    What is the function of the gingival sulcus?

    <p>It blocks bacteria from accessing deeper tissues.</p> Signup and view all the answers

    Which part of the tooth is responsible for creating the gomphosis articulation?

    <p>Periodontal ligament</p> Signup and view all the answers

    What distinguishes incisors from canines?

    <p>Canines have a sharp ridgeline and pointed tip.</p> Signup and view all the answers

    How many roots do premolars typically possess?

    <p>One or two</p> Signup and view all the answers

    Where is the apical foramen located?

    <p>At the opening of the root canal</p> Signup and view all the answers

    What does the root of a tooth sit in?

    <p>Alveolar bone</p> Signup and view all the answers

    Which of the following statements about the crown of a tooth is true?

    <p>It projects into the oral cavity from the surface of the gums.</p> Signup and view all the answers

    Which type of tooth is primarily used for crushing and grinding?

    <p>Premolars</p> Signup and view all the answers

    What is the primary function of molars?

    <p>Crushing and grinding food</p> Signup and view all the answers

    How many deciduous teeth does a child typically have by the age of 2?

    <p>20</p> Signup and view all the answers

    What are the third set of molars commonly referred to as?

    <p>Wisdom teeth</p> Signup and view all the answers

    Which of the following statements about permanent teeth is correct?

    <p>Three additional molars appear on each side of the upper and lower jaws.</p> Signup and view all the answers

    What common dental issue is associated with wisdom teeth?

    <p>Impacted teeth</p> Signup and view all the answers

    What distinguishes deciduous teeth from permanent teeth?

    <p>Deciduous teeth are also known as primary teeth.</p> Signup and view all the answers

    How many total permanent teeth are expected in a full set?

    <p>32</p> Signup and view all the answers

    Which of the following is not a characteristic of molars?

    <p>Single root structure</p> Signup and view all the answers

    What is the primary age by which a child typically has 20 deciduous teeth?

    <p>2 years</p> Signup and view all the answers

    How many total permanent teeth are usually present in an adult mouth?

    <p>32</p> Signup and view all the answers

    What happens to the roots of primary teeth as permanent teeth begin to replace them?

    <p>They erode</p> Signup and view all the answers

    Which type of tooth is particularly susceptible to impaction due to overcrowding?

    <p>Wisdom teeth</p> Signup and view all the answers

    What is the primary role of molars in the dental structure?

    <p>Crushing and grinding food</p> Signup and view all the answers

    What is the typical number of roots that upper jaw molars possess?

    <p>Three roots</p> Signup and view all the answers

    How many additional molars appear on each side of the upper and lower jaws after the primary teeth?

    <p>Three</p> Signup and view all the answers

    What term is used to describe a tooth that fails to erupt due to overcrowding?

    <p>Impacted tooth</p> Signup and view all the answers

    What is the primary function of the myenteric plexus?

    <p>To facilitate motor control of digestive muscle layers</p> Signup and view all the answers

    Which layer of the digestive tract is located between the circular and longitudinal muscle layers?

    <p>Muscularis externa</p> Signup and view all the answers

    What differentiates smooth muscle from skeletal and cardiac muscle at the cellular level?

    <p>Organization of actin and myosin filaments</p> Signup and view all the answers

    What is one of the roles of smooth muscle in the digestive tract?

    <p>To regulate the movement along passageways</p> Signup and view all the answers

    Which structural feature is characteristic of smooth muscle?

    <p>Formation of a loose network of sarcoplasmic reticulum</p> Signup and view all the answers

    What is the typical diameter of smooth muscle cells in the digestive tract?

    <p>5–10 µm</p> Signup and view all the answers

    Which type of neural plexus works with the myenteric plexus to coordinate digestive activity?

    <p>Submucosal plexus</p> Signup and view all the answers

    Which of the following best describes the arrangement of smooth muscle layers in the digestive tract?

    <p>The inner layer is circular and the outer layer is longitudinal</p> Signup and view all the answers

    Which mechanism is primarily responsible for propelling intestinal contents through the digestive tract?

    <p>Peristalsis</p> Signup and view all the answers

    What role do enteroendocrine cells play in digestive activities?

    <p>They secrete hormones that regulate digestive functions.</p> Signup and view all the answers

    Which part of the digestive tract is responsible for most nutrient absorption?

    <p>Small intestine</p> Signup and view all the answers

    What is the main function of segmentation in the digestive process?

    <p>To mix and churn food, increasing contact with digestive juices.</p> Signup and view all the answers

    Which structure plays a key role in the swallowing process?

    <p>Pharynx</p> Signup and view all the answers

    What is the significance of the mesenteries in the digestive system?

    <p>They provide support and anchorage for digestive organs.</p> Signup and view all the answers

    What is the primary role of the large intestine?

    <p>Formation and elimination of feces</p> Signup and view all the answers

    Which digestive hormone is primarily involved in stimulating gastric acid secretion?

    <p>Gastrin</p> Signup and view all the answers

    What is the primary function of the gingival sulcus?

    <p>To prevent bacteria from accessing deeper tissues</p> Signup and view all the answers

    Which characteristic distinguishes canines from incisors?

    <p>Conical shape with a sharp ridgeline</p> Signup and view all the answers

    What is the role of the cement in a tooth?

    <p>To cover the dentin in the root</p> Signup and view all the answers

    Which part of the tooth is located below the gum line?

    <p>Root</p> Signup and view all the answers

    Which type of tooth is primarily used for grinding and mashing food?

    <p>Premolars</p> Signup and view all the answers

    What structure creates the gomphosis articulation?

    <p>Periodontal ligament</p> Signup and view all the answers

    What is the primary role of the root canal in a tooth?

    <p>Passageway for nerves and blood vessels</p> Signup and view all the answers

    Which type of teeth are located at the front of the mouth and are useful for cutting?

    <p>Incisors</p> Signup and view all the answers

    What is a unique feature of thick filaments in smooth muscle compared to other muscle types?

    <p>Scattered throughout the sarcoplasm</p> Signup and view all the answers

    How do visceral smooth muscle cells contract?

    <p>In a wave as a single unit</p> Signup and view all the answers

    Where are multi-unit smooth muscle cells primarily located?

    <p>Walls of large arteries</p> Signup and view all the answers

    What type of smooth muscle lacks direct connections to motor neurons?

    <p>Visceral smooth muscle</p> Signup and view all the answers

    What stimulates visceral smooth muscle cells?

    <p>Neural, hormonal, or chemical stimulation</p> Signup and view all the answers

    What happens to the shape of a smooth muscle cell during contraction?

    <p>It twists like a corkscrew</p> Signup and view all the answers

    Which location is associated with multi-unit smooth muscle?

    <p>Iris of the eye</p> Signup and view all the answers

    What is a characteristic of dense bodies in smooth muscle cells?

    <p>They resemble Z lines in skeletal muscle</p> Signup and view all the answers

    What is the primary function of the mesentery in the digestive system?

    <p>To provide access routes for blood vessels, nerves, and lymphatics</p> Signup and view all the answers

    Which layer of the digestive tract contains a mucous membrane and areolar tissue?

    <p>Mucosa</p> Signup and view all the answers

    What type of tissue primarily composes the submucosa layer of the digestive tract?

    <p>Dense irregular connective tissue</p> Signup and view all the answers

    What is the main role of the muscular layer in the digestive tract?

    <p>To perform mechanical processing and movement</p> Signup and view all the answers

    Which layer of the digestive tract is absent in the oral cavity and esophagus?

    <p>Serosa</p> Signup and view all the answers

    What type of tissue are the cells of the muscular layer of the digestive tract primarily composed of?

    <p>Smooth muscle</p> Signup and view all the answers

    Which feature is characteristic of the large intestine wall?

    <p>Domination by mucin-secreting goblet cells</p> Signup and view all the answers

    What is the primary function of the serosa layer in the abdominal cavity?

    <p>To stabilize organs and prevent motion</p> Signup and view all the answers

    What is the main function of the mucus secreted by the goblet cells in the large intestine?

    <p>Lubricates feces as it becomes drier</p> Signup and view all the answers

    Which of the following best describes a key feature of the submucosa layer?

    <p>Houses blood vessels and lymphatic vessels</p> Signup and view all the answers

    What type of muscle is the internal anal sphincter composed of?

    <p>Smooth muscle</p> Signup and view all the answers

    Which of the following describes the external anal sphincter?

    <p>Under voluntary control</p> Signup and view all the answers

    What can increased venous pressure in the rectal area lead to?

    <p>Hemorrhoids</p> Signup and view all the answers

    What is the primary role of local factors in digestive activities?

    <p>Initiating physical changes in the digestive tract</p> Signup and view all the answers

    Which type of reflex is primarily involved in short neural control mechanisms of digestion?

    <p>Myenteric reflexes</p> Signup and view all the answers

    What distinguishes long reflexes in the digestive system?

    <p>They involve the central nervous system.</p> Signup and view all the answers

    Which of the following hormones does NOT typically influence digestive function?

    <p>Cortisol</p> Signup and view all the answers

    How does congenital megacolon (Hirschsprung disease) primarily affect the digestive system?

    <p>Paralysis of smooth muscle leading to constipation</p> Signup and view all the answers

    Which statement best describes the function of enteroendocrine cells?

    <p>They produce hormones that regulate digestive processes.</p> Signup and view all the answers

    What triggers the myenteric reflexes in the digestive tract?

    <p>Activation of stretch or chemoreceptors</p> Signup and view all the answers

    Which mechanism is primarily responsible for peristalsis in the digestive tract?

    <p>Coordinated contraction of smooth muscle layers</p> Signup and view all the answers

    What condition is characterized by the absence of peristaltic movement in the rectum?

    <p>Congenital megacolon</p> Signup and view all the answers

    What substance do chief cells secrete that is activated by HCl to become an active enzyme?

    <p>Pepsinogen</p> Signup and view all the answers

    How do parietal cells produce HCl without harming themselves?

    <p>By transporting H+ and Cl– ions separately</p> Signup and view all the answers

    What phenomenon describes the increase in blood pH due to the release of bicarbonate ions during active gastric secretion?

    <p>Alkaline tide</p> Signup and view all the answers

    Which enzyme is produced by newborns that aids in the digestion of milk?

    <p>Rennin</p> Signup and view all the answers

    What process occurs when bicarbonate is ejected into the interstitial fluid in exchange for chloride ions?

    <p>Bicarbonate secretion</p> Signup and view all the answers

    What initiates the dissociation of carbonic acid, leading to the formation of hydrogen ions?

    <p>Carbonic anhydrase activity</p> Signup and view all the answers

    What ion is primarily responsible for the acidic environment in the stomach due to its active transport into the gastric gland lumen?

    <p>Hydrogen</p> Signup and view all the answers

    Which of the following statements about bicarbonate in the context of gastric secretion is incorrect?

    <p>Bicarbonate is secreted inside the gastric glands.</p> Signup and view all the answers

    What is the primary role of pepsin in the stomach?

    <p>Digestion of proteins</p> Signup and view all the answers

    Which cell type is responsible for the secretion of hydrochloric acid in the stomach?

    <p>Parietal cells</p> Signup and view all the answers

    What is the role of the duodenum in digestive regulation?

    <p>It coordinates gastric activity and digestive secretion based on chyme.</p> Signup and view all the answers

    What would be the effect on intestinal contents' pH if secretin was not produced?

    <p>The pH would decrease, making it more acidic.</p> Signup and view all the answers

    How does a high-fat meal affect the level of cholecystokinin (CCK) in the blood?

    <p>It raises the level of CCK.</p> Signup and view all the answers

    What initiates the cephalic phase of gastric secretion?

    <p>The sight, smell, or thought of food.</p> Signup and view all the answers

    During the gastric phase of secretion, which stimulus contributes to the release of gastric juices?

    <p>Food arriving in the stomach.</p> Signup and view all the answers

    Which hormone is primarily responsible for the coordination of the digestive process?

    <p>Cholecystokinin</p> Signup and view all the answers

    In what scenario would the parasympathetic impulse stimulate gastric gland cells?

    <p>After consuming a meal high in protein.</p> Signup and view all the answers

    What effect does a decrease in gastric juice production have on the digestive process?

    <p>It slows down digestion.</p> Signup and view all the answers

    Which phase of gastric secretion is characterized by a brief duration and occurs as a response to sensory stimuli?

    <p>Cephalic phase</p> Signup and view all the answers

    What is the primary function of digestive hormones like secretin and cholecystokinin?

    <p>To coordinate digestive activities and enzyme secretion.</p> Signup and view all the answers

    What is the ability of smooth muscle to function over a wide range of lengths called?

    <p>Plasticity</p> Signup and view all the answers

    What mechanism primarily describes the wave of muscle contraction that propels food through the digestive tract?

    <p>Peristalsis</p> Signup and view all the answers

    Which characteristic differentiates smooth muscle contraction from skeletal muscle contraction?

    <p>Smooth muscle can contract over a wider range of resting lengths</p> Signup and view all the answers

    In which part of the digestive process does segmentation occur?

    <p>Small intestine and some large intestine areas</p> Signup and view all the answers

    What is NOT a characteristic of smooth muscle tone?

    <p>Constant tension regardless of conditions</p> Signup and view all the answers

    How do circular and longitudinal muscles function during peristalsis?

    <p>Circular muscles contract behind the bolus, longitudinal ahead</p> Signup and view all the answers

    What is the primary purpose of segmentation in the digestive system?

    <p>To churn and fragment bolus contents</p> Signup and view all the answers

    What structural feature is characteristic of smooth muscle fibers?

    <p>Scattered arrangement of thick and thin filaments</p> Signup and view all the answers

    Which statement correctly describes the major characteristics of the large intestine wall?

    <p>It features distinct intestinal glands with goblet cells.</p> Signup and view all the answers

    What is found in the anal canal that contributes to its distinct structural features?

    <p>Longitudinal folds referred to as anal columns.</p> Signup and view all the answers

    Which of the following statements about the anal sphincters is true?

    <p>The internal anal sphincter is not under voluntary control.</p> Signup and view all the answers

    Which condition can be caused by increased pressure in the veins of the rectum?

    <p>Hemorrhoids</p> Signup and view all the answers

    What is a primary function of mucus secreted by goblet cells in the large intestine?

    <p>To lubricate feces as they become drier.</p> Signup and view all the answers

    What shape does the sigmoid colon resemble?

    <p>S-shaped</p> Signup and view all the answers

    Where does the ascending colon begin?

    <p>At the cecum</p> Signup and view all the answers

    What structure supports the transverse colon?

    <p>Transverse mesocolon</p> Signup and view all the answers

    Which colon segment ends at the sigmoid flexure?

    <p>Descending colon</p> Signup and view all the answers

    Which of the following statements about the sigmoid colon is true?

    <p>It empties into the rectum.</p> Signup and view all the answers

    At which anatomical location does the ascending colon bend sharply?

    <p>Right colic flexure</p> Signup and view all the answers

    What is the approximate length of the sigmoid colon?

    <p>15 cm</p> Signup and view all the answers

    Which part of the colon crosses the abdomen from right to left?

    <p>Transverse colon</p> Signup and view all the answers

    Which colon section is retroperitoneal?

    <p>Descending colon</p> Signup and view all the answers

    What is the primary function of the sigmoid colon?

    <p>Store waste</p> Signup and view all the answers

    What initiates the esophageal phase of swallowing?

    <p>The entrance of the bolus into the esophagus</p> Signup and view all the answers

    What is the typical travel time for a bolus through the esophagus?

    <p>9 seconds</p> Signup and view all the answers

    What happens when a dry bolus is present during swallowing?

    <p>It requires secondary peristaltic waves</p> Signup and view all the answers

    What triggers the opening of the lower esophageal sphincter?

    <p>The approach of the bolus</p> Signup and view all the answers

    Which part of the digestive system is enclosed by the peritoneal cavity?

    <p>Stomach and most of the intestine</p> Signup and view all the answers

    What structure covers the organs enclosed by the peritoneal cavity?

    <p>Visceral peritoneum</p> Signup and view all the answers

    How much peritoneal fluid is typically secreted and reabsorbed daily?

    <p>7 liters</p> Signup and view all the answers

    What can accelerate the rate of fluid moving into the peritoneal cavity?

    <p>Liver disease, kidney disease, and heart failure</p> Signup and view all the answers

    What condition can arise from the accumulation of peritoneal fluid?

    <p>Ascites</p> Signup and view all the answers

    What barrier allows sliding movements without friction in the peritoneal cavity?

    <p>Serous membrane</p> Signup and view all the answers

    What marks the fixed portion of the tongue that projects into the oropharynx?

    <p>V-shaped line of vallate papillae</p> Signup and view all the answers

    Which structure attaches the gums to the upper lip?

    <p>Frenulum of the upper lip</p> Signup and view all the answers

    What provides extra support to the inferior boundary of the oral cavity?

    <p>Geniohyoid and mylohyoid muscles</p> Signup and view all the answers

    What is the space between the cheeks (or lips) and teeth called?

    <p>Oral vestibule</p> Signup and view all the answers

    Which of the following structures extends from the soft palate to the base of the tongue?

    <p>Palatoglossal arch</p> Signup and view all the answers

    What is the function of the thick mucosa covering the hard palate?

    <p>To facilitate food compression</p> Signup and view all the answers

    What is the role of gingivae in the oral cavity?

    <p>To provide a base for teeth</p> Signup and view all the answers

    What structure is located on either side of the uvula?

    <p>Palatopharyngeal arch</p> Signup and view all the answers

    Which part of the tongue is characterized by being anterior and mobile?

    <p>Body of the tongue</p> Signup and view all the answers

    What is the primary function of the frenulum of the lower lip?

    <p>To attach the gums to the lower lip</p> Signup and view all the answers

    What is the primary function of the sigmoid colon?

    <p>Stores fecal matter</p> Signup and view all the answers

    Which part of the colon is ascribed to the right colic flexure?

    <p>Ascending colon</p> Signup and view all the answers

    What does the transverse colon primarily connect?

    <p>Ascending colon and descending colon</p> Signup and view all the answers

    How long is the sigmoid colon approximately?

    <p>15 cm</p> Signup and view all the answers

    Which colon segment is retroperitoneal and attached to the abdominal wall?

    <p>Ascending colon</p> Signup and view all the answers

    What is the primary function of smooth muscle tissue in the digestive system?

    <p>Propulsion of materials through the digestive tract</p> Signup and view all the answers

    Which of the following statements best describes the structural features of the digestive tract?

    <p>It is composed of four main layers</p> Signup and view all the answers

    What is one of the key functions of the accessory organs in the digestive system?

    <p>Production of bile and digestive enzymes</p> Signup and view all the answers

    How do materials primarily move through the digestive tract?

    <p>Through rhythmic contractions of muscle layers</p> Signup and view all the answers

    Which component is NOT considered a major organ of the digestive system?

    <p>Spleen</p> Signup and view all the answers

    What role do enteroendocrine cells play in the digestive system?

    <p>They regulate digestive hormone secretion</p> Signup and view all the answers

    Which of the following correctly describes the digestive tract's histology?

    <p>Contains layers of muscle and connective tissue</p> Signup and view all the answers

    Which specific structural feature is characteristic of smooth muscle found in the digestive tract?

    <p>Spindle-shaped cells</p> Signup and view all the answers

    What are considered local factors in digestive activities?

    <p>Presence of chemicals in the digestive tract</p> Signup and view all the answers

    Which of the following describes short reflexes in digestive control mechanisms?

    <p>Triggered by stretch or chemoreceptors in the digestive tract</p> Signup and view all the answers

    What is a key characteristic of long reflexes in digestive regulation?

    <p>Involve interneurons and CNS motor neurons</p> Signup and view all the answers

    How many hormones are involved in hormonal control mechanisms of digestive function?

    <p>18</p> Signup and view all the answers

    What characterizes congenital megacolon (Hirschsprung disease)?

    <p>Absence or reduction of ganglion cells in the myenteric plexus</p> Signup and view all the answers

    Which of the following mechanisms does NOT play a role in regulating digestive activities?

    <p>External environmental factors</p> Signup and view all the answers

    What condition is associated with a lack of peristaltic movement in the intestine?

    <p>Congenital megacolon</p> Signup and view all the answers

    What triggers the activation of short reflexes in the digestive tract?

    <p>Mechanical stretching of the digestive tract wall</p> Signup and view all the answers

    What role do enteroendocrine cells serve in the digestive system?

    <p>Producing digestive hormones</p> Signup and view all the answers

    What is the primary function of the large intestine?

    <p>Reabsorbing water and compacting intestinal contents into feces</p> Signup and view all the answers

    Which segment of the large intestine is responsible for collecting and beginning the compaction of material?

    <p>Cecum</p> Signup and view all the answers

    Which of the following regions is NOT a part of the colon?

    <p>Ileum</p> Signup and view all the answers

    What is the primary role of the appendix, also known as the vermiform appendix?

    <p>Functions as a lymphoid organ</p> Signup and view all the answers

    What characteristic of the large intestine distinguishes its wall from that of the small intestine?

    <p>Thinner wall and larger diameter</p> Signup and view all the answers

    What triggers the gastric phase of secretion?

    <p>Presence of undigested materials in the stomach</p> Signup and view all the answers

    What is a key effect of gastrin secretion during the gastric phase?

    <p>Increases mixing waves of stomach contractions</p> Signup and view all the answers

    What is the role of bacterial action in the large intestine?

    <p>Generating important vitamins</p> Signup and view all the answers

    Which portion of the large intestine is directly connected to the small intestine via the ileocecal valve?

    <p>Cecum</p> Signup and view all the answers

    What initiates the intestinal phase of gastric secretion?

    <p>Chyme entering the duodenum</p> Signup and view all the answers

    Which of the following occurs during the intestinal phase of gastric secretion?

    <p>Inhibition of gastrin production</p> Signup and view all the answers

    What is the average length of the large intestine?

    <p>1.5 m</p> Signup and view all the answers

    Which function is primarily associated with the rectum of the large intestine?

    <p>Storing fecal material prior to defecation</p> Signup and view all the answers

    What occurs as a result of distention of the duodenum?

    <p>Initiation of the enterogastric reflex</p> Signup and view all the answers

    What is a consequence of the intestinal phase on gastric activity?

    <p>It decreases gastric motility</p> Signup and view all the answers

    Which of the following is NOT a major function of the large intestine?

    <p>Secreting digestive enzymes</p> Signup and view all the answers

    Which reflex is stimulated by the stretching of the stomach wall?

    <p>Gastroenteric reflex</p> Signup and view all the answers

    What increases in the duodenum during the intestinal phase?

    <p>Mucus production</p> Signup and view all the answers

    How long does the gastric phase typically last?

    <p>2–4 hours</p> Signup and view all the answers

    What role does gastrin play in stomach function?

    <p>Stimulates secretion from parietal and chief cells</p> Signup and view all the answers

    What function does the rectum serve in the digestive system?

    <p>Temporarily stores fecal material</p> Signup and view all the answers

    What are haustra in the large intestine responsible for?

    <p>Creating pouches in the colon wall</p> Signup and view all the answers

    Which structure corresponds with the outer layer of the muscularis externa in the colon?

    <p>Tenia coli</p> Signup and view all the answers

    What triggers mass movements in the large intestine?

    <p>Expansion of the stomach and duodenum</p> Signup and view all the answers

    How do omental appendices contribute to the structure of the colon?

    <p>Provide structural support to the colon</p> Signup and view all the answers

    What is the primary role of the myenteric plexus in the digestive tract?

    <p>To coordinate movements of smooth muscle</p> Signup and view all the answers

    Which statement accurately describes smooth muscle organization in the digestive tract?

    <p>Smooth muscle consists of both inner circular and outer longitudinal layers.</p> Signup and view all the answers

    Which characteristic of smooth muscle cells differentiates them from skeletal and cardiac muscle cells?

    <p>Lack of sarcomeres and striations</p> Signup and view all the answers

    Where is the myenteric plexus located within the digestive tract?

    <p>Between the circular and longitudinal muscle layers</p> Signup and view all the answers

    What are the lengths typically observed for smooth muscle cells in the digestive tract?

    <p>30–200 µm</p> Signup and view all the answers

    What structure works in conjunction with the myenteric plexus to control digestive activity?

    <p>Submucosal plexus</p> Signup and view all the answers

    Which of the following features is NOT characteristic of smooth muscle tissue?

    <p>Formation of well-defined striations</p> Signup and view all the answers

    How do the sensory neurons in the myenteric plexus contribute to digestive function?

    <p>They coordinate muscular contractions based on stretch and chemical signals.</p> Signup and view all the answers

    What is the primary function of the esophagus in the digestive tract?

    <p>Transport of materials to the stomach</p> Signup and view all the answers

    Which function of the digestive tract involves the release of enzymes and digestive juices?

    <p>Secretion</p> Signup and view all the answers

    Which part of the digestive tract is primarily responsible for enzymatic digestion and absorption?

    <p>Small intestine</p> Signup and view all the answers

    What is the primary role of the large intestine in the digestive process?

    <p>Dehydration and compaction of indigestible materials</p> Signup and view all the answers

    What process describes the movement of nutrients across the digestive epithelium into the bloodstream?

    <p>Absorption</p> Signup and view all the answers

    Which statement accurately describes mechanical digestion?

    <p>It includes crushing and shredding food in the mouth.</p> Signup and view all the answers

    Which digestive process occurs when solid food and liquids enter the oral cavity?

    <p>Ingestion</p> Signup and view all the answers

    Which organ is primarily involved in the chemical breakdown of food?

    <p>Stomach</p> Signup and view all the answers

    What is the main role of the pharynx in the digestive process?

    <p>To propel food into the esophagus</p> Signup and view all the answers

    Which of the following best describes chemical digestion?

    <p>Hydrolysis of molecules into absorbable units</p> Signup and view all the answers

    What primarily increases the absorptive capacity of the intestinal tract?

    <p>Circular folds</p> Signup and view all the answers

    What role do Paneth cells play in the intestinal glands?

    <p>Protection against pathogens</p> Signup and view all the answers

    What allows chylomicrons to be transported from the intestinal tract?

    <p>Lymphatic capillaries</p> Signup and view all the answers

    Which region of the small intestine contains most of the circular folds?

    <p>Jejunum</p> Signup and view all the answers

    What type of cells in intestinal glands divide to produce new epithelial cells?

    <p>Stem cells</p> Signup and view all the answers

    What structure in the intestinal villus is responsible for carrying absorbed nutrients?

    <p>Capillary network</p> Signup and view all the answers

    What characterizes the epithelial surface of intestinal villi?

    <p>Microvilli</p> Signup and view all the answers

    Which of the following functions does not occur at the base of intestinal glands?

    <p>Absorption of nutrients</p> Signup and view all the answers

    What type of projections do intestinal villi exhibit?

    <p>Fingerlike projections</p> Signup and view all the answers

    What do lymphatic capillaries transport that blood capillaries cannot?

    <p>Large protein-lipid packages</p> Signup and view all the answers

    What is the role of the periodontal ligament in a tooth?

    <p>Connects the root dentin to the alveolar bone</p> Signup and view all the answers

    Which feature distinguishes the cement from dentin in teeth?

    <p>Cement is less resistant to erosion than dentin</p> Signup and view all the answers

    What anatomical structure acts as the boundary between the crown and the root of a tooth?

    <p>Neck</p> Signup and view all the answers

    What type of tooth is primarily associated with tearing or slashing food?

    <p>Canines</p> Signup and view all the answers

    Where are blood vessels and nerves located within a tooth?

    <p>Pulp cavity</p> Signup and view all the answers

    What is the primary function of the gingival sulcus?

    <p>To prevent bacterial access to the root</p> Signup and view all the answers

    What distinguishes premolars from other types of teeth?

    <p>They typically have one or two roots and flat crowns</p> Signup and view all the answers

    What is a defining characteristic of incisors?

    <p>They have a single root and a blade-like shape</p> Signup and view all the answers

    What role does the apical foramen serve in a tooth?

    <p>It is the opening for nerves and blood vessels into the pulp cavity</p> Signup and view all the answers

    What differentiates the root from the crown of a tooth?

    <p>The root is embedded in the alveolar bone below the gum line</p> Signup and view all the answers

    What is the primary role of gastrin during the gastric phase of digestion?

    <p>Increasing secretion by parietal and chief cells</p> Signup and view all the answers

    Which physiological response is triggered by the distention of the duodenum during the intestinal phase?

    <p>Activation of the enterogastric reflex</p> Signup and view all the answers

    During the gastric phase, the presence of undigested materials in the stomach primarily affects which process?

    <p>Gastrin secretion</p> Signup and view all the answers

    What effect does the release of gastrin have on gastric motility?

    <p>Increases gastric motility</p> Signup and view all the answers

    Which condition is primarily influenced by the contraction of the pyloric sphincter during the intestinal phase?

    <p>Decreased chyme release into the duodenum</p> Signup and view all the answers

    What is the function of the esophagus?

    <p>To actively transport food and liquids to the stomach</p> Signup and view all the answers

    Which statement accurately describes the structural dimensions of the esophagus?

    <p>It is a hollow tube about 25 cm long and 2 cm wide</p> Signup and view all the answers

    Which of the following statements about the pharynx is true?

    <p>It serves as a passageway for food, liquid, and air</p> Signup and view all the answers

    What role does the upper esophageal sphincter serve?

    <p>It prevents air from entering the esophagus</p> Signup and view all the answers

    Which part of the pharynx is located posterior to the oral cavity?

    <p>Oropharynx</p> Signup and view all the answers

    What function do the sympathetic and parasympathetic fibers serve in the esophagus?

    <p>They maintain resting muscle tone in the circular muscle layer</p> Signup and view all the answers

    Where does the esophagus enter the abdominopelvic cavity?

    <p>Through the diaphragmatic hiatus</p> Signup and view all the answers

    What is the primary function of the lower esophageal sphincter?

    <p>Prevents backflow of stomach contents</p> Signup and view all the answers

    What is the primary function of the smooth muscle in the muscularis mucosae of the intestinal tract?

    <p>To move villi back and forth</p> Signup and view all the answers

    Which of the following best describes the role of the brush border in the small intestine?

    <p>It increases surface area for absorption</p> Signup and view all the answers

    Which statement accurately reflects the distribution of nutrient absorption in the intestines?

    <p>About 90% occurs in the small intestine</p> Signup and view all the answers

    What are the three segments of the small intestine?

    <p>Duodenum, jejunum, ileum</p> Signup and view all the answers

    What is the average length of the small intestine?

    <p>6 m (19.7 ft)</p> Signup and view all the answers

    What specialized structure within the villi assists in the movement of lymph?

    <p>Lacteal</p> Signup and view all the answers

    What is the primary function of the lacteals found in the intestinal tract?

    <p>To transport fat-soluble nutrients</p> Signup and view all the answers

    What is the diameter of the small intestine at its widest point?

    <p>4 cm (1.6 in.)</p> Signup and view all the answers

    Which of the following structures is primarily involved in increasing the absorption surface area in the small intestine?

    <p>Microvilli</p> Signup and view all the answers

    What anatomical feature is responsible for the actual absorption of digested nutrients?

    <p>Epithelial cells in the villi</p> Signup and view all the answers

    What is the primary role of the duodenum in the digestive process?

    <p>Neutralization of acidic chyme</p> Signup and view all the answers

    Which characteristic is NOT true of the jejunum?

    <p>Located in the retroperitoneal space</p> Signup and view all the answers

    Which segment of the small intestine has the longest length?

    <p>Ileum</p> Signup and view all the answers

    What type of secretions are produced by duodenal glands?

    <p>Mucous secretions</p> Signup and view all the answers

    What is the main anatomical feature distinguishing the ileum from other segments?

    <p>Presence of aggregated lymphoid nodules</p> Signup and view all the answers

    Which segment of the small intestine is primarily responsible for nutrient absorption?

    <p>Jejunum</p> Signup and view all the answers

    In which region of the body is the duodenum primarily located?

    <p>In the retroperitoneal space</p> Signup and view all the answers

    What is a significant anatomical feature of the ileum?

    <p>Presence of Peyer's patches</p> Signup and view all the answers

    What impacts the function of the ileocecal valve?

    <p>Controls flow from the ileum to the cecum</p> Signup and view all the answers

    Which of the following describes the villi found in the duodenum?

    <p>Relatively small and few</p> Signup and view all the answers

    What is the primary role of intestinal villi in nutrient absorption?

    <p>To increase surface area for absorption of nutrients</p> Signup and view all the answers

    Which of the following correctly describes the function of Paneth cells located at the base of intestinal glands?

    <p>They release substances that contribute to innate immunity</p> Signup and view all the answers

    What is the function of the extensive capillary network found in the lamina propria of a villus?

    <p>To carry absorbed nutrients to the hepatic portal circulation</p> Signup and view all the answers

    Which type of structure primarily increases the absorptive surface area of the small intestine?

    <p>Circular folds (plicae circulares)</p> Signup and view all the answers

    What is the primary reason that absorbed fatty acids are transported via the lymphatic system instead of entering blood capillaries directly?

    <p>Fatty acids need to be converted into chylomicrons for absorption</p> Signup and view all the answers

    Which characteristic distinguishes microvilli from intestinal villi?

    <p>Microvilli enhance the absorbent area more than villi</p> Signup and view all the answers

    What key feature of the intestinal glands aids in replenishing the epithelial cells of the intestine?

    <p>Stem cells dividing and producing new epithelial cells</p> Signup and view all the answers

    How do intestinal structures such as circular folds contribute to nutrient absorption?

    <p>They slow down the passage of food to maximize absorption time</p> Signup and view all the answers

    What specific type of tissue covers the surfaces of intestinal villi?

    <p>Epithelial tissue</p> Signup and view all the answers

    What is the primary function of the esophagus?

    <p>To actively move food and liquids to the stomach</p> Signup and view all the answers

    Which region of the pharynx is located posterior to the mouth?

    <p>Oropharynx</p> Signup and view all the answers

    What maintains the resting muscle tone in the circular muscle layer of the esophagus?

    <p>Parasympathetic and sympathetic fibers</p> Signup and view all the answers

    At which location does the esophagus enter the abdominopelvic cavity?

    <p>Esophageal hiatus</p> Signup and view all the answers

    Which type of muscle does the upper esophageal sphincter consist of?

    <p>Skeletal muscle</p> Signup and view all the answers

    What is the consequence of the lower esophageal sphincter normally being contracted?

    <p>Prevents backflow of stomach contents</p> Signup and view all the answers

    How long is the esophagus in adults on average?

    <p>25 cm</p> Signup and view all the answers

    What is the narrowest point of the esophagus located near?

    <p>The cricoid cartilage</p> Signup and view all the answers

    What is the primary protective feature of the mucosa layer in the stomach wall?

    <p>Production of alkaline mucus</p> Signup and view all the answers

    Which type of cell in the gastric glands is primarily responsible for secreting hydrochloric acid?

    <p>Parietal cells</p> Signup and view all the answers

    What is the typical lifespan of a gastric epithelial cell in the stomach?

    <p>3–7 days</p> Signup and view all the answers

    Which layer of the stomach wall contains the muscular layer that includes oblique, circular, and longitudinal muscles?

    <p>Muscular layer</p> Signup and view all the answers

    What type of secretion is primarily produced by the gastric glands located in the pylorus?

    <p>Mucus and hormones</p> Signup and view all the answers

    Which layer of the esophageal wall is responsible for allowing expansion during the passage of a bolus?

    <p>Submucosa</p> Signup and view all the answers

    In which phase of swallowing does the tongue first push the bolus into the oropharynx?

    <p>Buccal phase</p> Signup and view all the answers

    What type of muscle comprises the superior third of the esophagus?

    <p>Skeletal muscle</p> Signup and view all the answers

    What triggers the reflex response during the buccal phase of swallowing?

    <p>Entry into the oropharynx</p> Signup and view all the answers

    Which structure elevates during the pharyngeal phase to prevent food from entering the nasopharynx?

    <p>Soft palate</p> Signup and view all the answers

    What is the primary function of the adventitia in the esophageal wall?

    <p>Anchoring the esophagus</p> Signup and view all the answers

    In the esophagus, how does the muscularis externa differ between its three regions?

    <p>It transitions from skeletal to mixed to smooth muscle</p> Signup and view all the answers

    What muscle contraction is coordinated by the swallowing center located in the medulla oblongata?

    <p>Pharyngeal muscle contraction</p> Signup and view all the answers

    During the swallowing process, what position does the epiglottis take?

    <p>It is folded down</p> Signup and view all the answers

    Which phase of swallowing is strictly voluntary?

    <p>Buccal phase</p> Signup and view all the answers

    Which of the following accurately describes the digestive system?

    <p>It includes the digestive tract and accessory organs.</p> Signup and view all the answers

    What is the primary function of the digestive system?

    <p>To supply nutrients for cell maintenance and growth.</p> Signup and view all the answers

    Which systems work in conjunction with the digestive system to support cellular functions?

    <p>Cardiovascular and urinary systems.</p> Signup and view all the answers

    What distinguishes the digestive tract's structure?

    <p>It has regions with permanent ridges and temporary folds.</p> Signup and view all the answers

    Which statement is true regarding accessory organs of the digestive system?

    <p>They produce enzymes secreted into the digestive tract.</p> Signup and view all the answers

    What role does the urinary system play in relation to the digestive system?

    <p>It removes waste products generated by cell activity.</p> Signup and view all the answers

    Why are the features of ridges and folds significant in the digestive tract?

    <p>They increase the surface area for nutrient absorption.</p> Signup and view all the answers

    What is a primary characteristic of the gastrointestinal (GI) tract?

    <p>It allows for food transmission from mouth to anus.</p> Signup and view all the answers

    Which statement best describes the accessory organs of digestion?

    <p>They secrete products required for the digestion process.</p> Signup and view all the answers

    What is the primary purpose of the digestive system working with other body systems?

    <p>To ensure proper nutrition and waste management.</p> Signup and view all the answers

    What initiates the esophageal phase of swallowing?

    <p>The bolus being forced through the entrance to the esophagus</p> Signup and view all the answers

    How does a dry bolus affect the swallowing process?

    <p>It may necessitate secondary peristaltic waves</p> Signup and view all the answers

    What is the typical travel time for a bolus through the esophagus?

    <p>9 seconds</p> Signup and view all the answers

    What triggers the opening of the lower esophageal sphincter?

    <p>The approach of the bolus</p> Signup and view all the answers

    Which part of the peritoneal membrane covers the organs within the peritoneal cavity?

    <p>Visceral peritoneum</p> Signup and view all the answers

    What is the main function of the peritoneal fluid?

    <p>To facilitate movement between the parietal and visceral layers</p> Signup and view all the answers

    What volume of peritoneal fluid is typically present in the peritoneal cavity at any given time?

    <p>50 mL</p> Signup and view all the answers

    What condition may result from an accumulation of peritoneal fluid?

    <p>Ascites</p> Signup and view all the answers

    Which factor can accelerate the fluid movement into the peritoneal cavity?

    <p>Liver disease</p> Signup and view all the answers

    Which layer lines the inner surface of the peritoneal cavity?

    <p>Parietal peritoneum</p> Signup and view all the answers

    What type of muscle composes the superior third of the esophagus?

    <p>Skeletal muscle</p> Signup and view all the answers

    What occurs during the buccal phase of swallowing?

    <p>The bolus is compressed against the hard palate.</p> Signup and view all the answers

    Which layer of the esophageal wall is responsible for expansion with the passage of a bolus?

    <p>Mucosa and submucosa</p> Signup and view all the answers

    Which phase of swallowing is considered strictly voluntary?

    <p>Buccal phase</p> Signup and view all the answers

    What is the function of the adventitia in the esophagus?

    <p>Anchors the esophagus to the posterior body wall</p> Signup and view all the answers

    During which phase of swallowing is the larynx elevated?

    <p>Pharyngeal phase</p> Signup and view all the answers

    What type of muscle comprises the inferior third of the esophagus?

    <p>Smooth muscle only</p> Signup and view all the answers

    Which of the following is a characteristic of the pharyngeal phase of swallowing?

    <p>It involves tactile receptors triggering motor commands.</p> Signup and view all the answers

    What age do children typically have 20 deciduous teeth?

    <p>2 years</p> Signup and view all the answers

    How many total permanent teeth are usually present in an adult mouth?

    <p>32</p> Signup and view all the answers

    What is the name given to the third set of molars?

    <p>Wisdom teeth</p> Signup and view all the answers

    What happens to primary teeth as permanent teeth begin to erupt?

    <p>They are pushed aside or fall out</p> Signup and view all the answers

    What conditions could lead to a tooth becoming impacted?

    <p>Overcrowding from adjacent teeth</p> Signup and view all the answers

    How many additional molars appear on each side of the upper and lower jaws after primary teeth?

    <p>3</p> Signup and view all the answers

    What is the main function of molars?

    <p>Crushing and grinding</p> Signup and view all the answers

    What is one of the major functions of the large intestine?

    <p>Reabsorbing water</p> Signup and view all the answers

    What common dental issue is especially associated with wisdom teeth?

    <p>Impaction</p> Signup and view all the answers

    Which segment of the large intestine primarily begins the process of compaction?

    <p>Cecum</p> Signup and view all the answers

    Which type of teeth are sometimes referred to as baby teeth?

    <p>Primary teeth</p> Signup and view all the answers

    What structure is attached to the cecum and functions as a lymphoid organ?

    <p>Appendix</p> Signup and view all the answers

    What number of roots do upper jaw molars typically have?

    <p>3</p> Signup and view all the answers

    Which of the following describes the general diameter and wall thickness of the colon compared to the small intestine?

    <p>Larger diameter and thinner walls</p> Signup and view all the answers

    What is the average length of the large intestine?

    <p>1.5 m</p> Signup and view all the answers

    What is the main role of the tongue in the oral cavity?

    <p>To manipulate materials inside the mouth</p> Signup and view all the answers

    Which component contributes to the formation and resistance to decay of enamel?

    <p>Calcium phosphate</p> Signup and view all the answers

    What condition is typically caused by a frenulum that is too short?

    <p>Ankyloglossia</p> Signup and view all the answers

    What does the fauces connect?

    <p>Oral cavity and oropharynx</p> Signup and view all the answers

    Which substance is NOT contained in the secretions that flush the surface of the tongue?

    <p>Vitamins</p> Signup and view all the answers

    What is the main composition of the bulk of each tooth?

    <p>Dentin</p> Signup and view all the answers

    What is the role of the occlusal surface of a tooth?

    <p>Crushing and slicing food</p> Signup and view all the answers

    What is required for the formation of enamel?

    <p>Calcium</p> Signup and view all the answers

    What is the primary function of the stomach's pylorus?

    <p>To regulate the passage of chyme into the small intestine</p> Signup and view all the answers

    What is located in the interior chamber of the tooth?

    <p>Pulp cavity</p> Signup and view all the answers

    Which mesentery is attached to the lesser curvature of the stomach?

    <p>Lesser omentum</p> Signup and view all the answers

    What can result from ankyloglossia in newborns?

    <p>Interference with breastfeeding</p> Signup and view all the answers

    What is chyme primarily composed of?

    <p>Food, saliva, and gastric gland secretions</p> Signup and view all the answers

    Which stomach region functions mainly as a mixing bowl?

    <p>Body</p> Signup and view all the answers

    How much material can the stomach typically hold when full?

    <p>1.5 liters</p> Signup and view all the answers

    What is the role of the cardia region of the stomach?

    <p>To secrete mucus for protection</p> Signup and view all the answers

    What shape does the stomach take when it is empty?

    <p>Muscular tube with constricted lumen</p> Signup and view all the answers

    Which curvature of the stomach forms the medial surface?

    <p>Lesser curvature</p> Signup and view all the answers

    What is the potential volume of material the stomach can hold at maximum capacity?

    <p>1,500 ml</p> Signup and view all the answers

    Which stomach region is located superior to the junction between the stomach and esophagus?

    <p>Fundus</p> Signup and view all the answers

    What type of epithelium is found at the beginning and end of the digestive tract?

    <p>Stratified squamous epithelium</p> Signup and view all the answers

    What structure increases the surface area for absorption in the mucosa?

    <p>Villi</p> Signup and view all the answers

    Which component of the mucosa contains blood vessels and sensory nerve endings?

    <p>Lamina propria</p> Signup and view all the answers

    What are the two layers that make up the muscularis mucosae?

    <p>Inner circular layer and outer longitudinal layer</p> Signup and view all the answers

    Which type of stimulation decreases digestive muscle tone and activity?

    <p>Sympathetic stimulation</p> Signup and view all the answers

    What structure consists of permanent transverse folds in the intestinal lining?

    <p>Plicae circulares</p> Signup and view all the answers

    What is the primary function of the submucosal neural plexus?

    <p>To innervate the mucosa and submucosa</p> Signup and view all the answers

    Which part of the digestive system primarily involves sensory neurons and autonomic nerve fibers?

    <p>Submucosal neural plexus</p> Signup and view all the answers

    What role does the duodenum play in the digestive process?

    <p>It regulates gastric activity and digestive secretion.</p> Signup and view all the answers

    Which phase of gastric secretion is triggered by the sight or smell of food?

    <p>Cephalic phase</p> Signup and view all the answers

    What is the function of secretin in the digestive process?

    <p>It helps regulate the water content in chyme.</p> Signup and view all the answers

    What triggers the gastric phase of secretion?

    <p>Distention of the stomach</p> Signup and view all the answers

    How does a high-fat meal affect levels of cholecystokinin (CCK) in the blood?

    <p>It raises levels.</p> Signup and view all the answers

    What is the primary function of the tongue in the oral cavity?

    <p>To manipulate materials inside the mouth</p> Signup and view all the answers

    What does the frenulum of the tongue do?

    <p>Connects the tongue to the floor of the mouth</p> Signup and view all the answers

    What is an effect of ankyloglossia?

    <p>Challenges with breastfeeding</p> Signup and view all the answers

    Which part of a tooth is primarily responsible for covering the dentin?

    <p>Enamel</p> Signup and view all the answers

    What is contained in the secretions of the small glands on the tongue?

    <p>Water, mucins, and lingual lipase</p> Signup and view all the answers

    What substance is primarily found in the pulp cavity of a tooth?

    <p>Vascular and nerve components</p> Signup and view all the answers

    Which statement about enamel is correct?

    <p>It's the hardest biologically manufactured substance</p> Signup and view all the answers

    What is the role of the occlusal surface of a tooth?

    <p>To facilitate slicing and chewing food</p> Signup and view all the answers

    What materials are necessary for the formation of enamel?

    <p>Calcium, phosphate, and vitamin D</p> Signup and view all the answers

    What is the composition of dentin?

    <p>A mineralized matrix similar to bone</p> Signup and view all the answers

    What is the main purpose of the gingival sulcus?

    <p>To block bacteria from accessing deeper tissues.</p> Signup and view all the answers

    Which tooth region is located below the gum line?

    <p>Root</p> Signup and view all the answers

    Which type of tooth is characterized by a blade shape and is primarily used for clipping?

    <p>Incisors</p> Signup and view all the answers

    What is the characteristic feature of canines?

    <p>Conical shape with a sharp ridgeline</p> Signup and view all the answers

    How many roots can premolars have?

    <p>One</p> Signup and view all the answers

    Which structure creates the gomphosis articulation in a tooth?

    <p>Periodontal ligament</p> Signup and view all the answers

    What is the role of the root canal in a tooth?

    <p>To house blood vessels and nerves.</p> Signup and view all the answers

    Which of the following statements about cement is true?

    <p>It covers the dentin in the root.</p> Signup and view all the answers

    What is the function of the apical foramen in a tooth?

    <p>To allow blood vessels and nerves to enter the root canal.</p> Signup and view all the answers

    Which tooth type is primarily used for grinding and mashing food?

    <p>Molars</p> Signup and view all the answers

    What is the primary function of the digestive system?

    <p>To break down food and absorb nutrients</p> Signup and view all the answers

    Which of the following is an accessory organ of the digestive system?

    <p>Liver</p> Signup and view all the answers

    Which layer of the digestive tract is responsible for peristalsis?

    <p>Circular muscle layer</p> Signup and view all the answers

    Which process primarily occurs in the small intestine?

    <p>Nutrient absorption</p> Signup and view all the answers

    What type of muscle tissue is primarily involved in the movements of the digestive tract?

    <p>Smooth muscle</p> Signup and view all the answers

    What role do enteroendocrine cells play in digestion?

    <p>Regulate digestive hormones</p> Signup and view all the answers

    Which of the following features distinguishes smooth muscle from skeletal muscle?

    <p>Single nucleus per cell</p> Signup and view all the answers

    Which structure is primarily involved in the swallowing process?

    <p>Pharynx</p> Signup and view all the answers

    What is the primary function of segmentation in the digestive process?

    <p>Mixing and churning food</p> Signup and view all the answers

    Which part of the digestive system has the most significant role in water absorption?

    <p>Large intestine</p> Signup and view all the answers

    What are the major functions of the large intestine?

    <p>Absorption of water and electrolytes, compaction of fecal material, and elimination of feces.</p> Signup and view all the answers

    What are the four regions of the colon?

    <p>Ascending colon, transverse colon, descending colon, sigmoid colon.</p> Signup and view all the answers

    What are mass movements in the large intestine?

    <p>Powerful peristaltic contractions that push materials along the distal portion of the large intestine.</p> Signup and view all the answers

    The wall of the large intestine contains villi.

    <p>False</p> Signup and view all the answers

    What types of cells dominate the intestinal glands of the large intestine?

    <p>Mucin-secreting goblet cells.</p> Signup and view all the answers

    What is the primary function of the internal anal sphincter?

    <p>To control the involuntary release of feces.</p> Signup and view all the answers

    What type of muscle is the external anal sphincter composed of?

    <p>Skeletal muscle.</p> Signup and view all the answers

    What happens to the epithelium at the anus?

    <p>It becomes keratinized.</p> Signup and view all the answers

    Increased venous pressure in the rectum can lead to hemorrhoids.

    <p>True</p> Signup and view all the answers

    What are the major and accessory organs of the digestive system?

    <p>Major organs include the mouth, esophagus, stomach, small intestine, large intestine, rectum, and anus. Accessory organs include the liver, pancreas, and gallbladder.</p> Signup and view all the answers

    The digestive tract begins at the ______ and ends at the ______.

    <p>mouth, anus</p> Signup and view all the answers

    The four major layers of the digestive tract are mucosa, ______, muscular layer, and ______.

    <p>submucosa, serosa</p> Signup and view all the answers

    Which of the following is NOT a layer of the digestive tract?

    <p>Epithelia</p> Signup and view all the answers

    What is peristalsis?

    <p>Peristalsis is a wave of muscle contraction that propels food along the digestive tract.</p> Signup and view all the answers

    Smooth muscle cells contain striations.

    <p>False</p> Signup and view all the answers

    Which type of smooth muscle is organized into sheets or layers?

    <p>Visceral smooth muscle</p> Signup and view all the answers

    What components are found in the lamina propria of the mucosa?

    <p>The lamina propria contains areolar tissue, blood vessels, sensory nerve endings, lymphatic vessels, smooth muscle cells, and some mucous glands.</p> Signup and view all the answers

    What are the primary stimuli for digestive activities?

    <p>Changes in pH of contents</p> Signup and view all the answers

    What are the hormonal control mechanisms involved in digestive function?

    <p>At least 18 hormones produced by enteroendocrine cells.</p> Signup and view all the answers

    What characterizes congenital megacolon (Hirschsprung disease)?

    <p>Absence or marked reduction in the number of ganglion cells in the myenteric plexus of the rectum.</p> Signup and view all the answers

    Which mechanism is more efficient for propelling intestinal contents along the digestive tract?

    <p>Peristalsis</p> Signup and view all the answers

    What are the major mechanisms that regulate and control digestive activities?

    <p>Hormonal and neural mechanisms.</p> Signup and view all the answers

    Describe enteroendocrine cells.

    <p>Endocrine cells in the epithelium of the digestive tract that produce hormones.</p> Signup and view all the answers

    What is ingestion?

    <p>The process when solid food and liquid enter the oral cavity.</p> Signup and view all the answers

    What is the primary function of the esophagus?

    <p>Transport of materials to the stomach.</p> Signup and view all the answers

    What is the role of the stomach in digestion?

    <p>Chemical breakdown and mechanical processing.</p> Signup and view all the answers

    What type of epithelium lines the oral cavity?

    <p>Stratified squamous</p> Signup and view all the answers

    What are the four types of teeth?

    <p>Incisors, canines, premolars, and molars.</p> Signup and view all the answers

    What is an impacted tooth?

    <p>A tooth that fails to erupt due to overcrowding or twisting in the jaw.</p> Signup and view all the answers

    What is the function of the esophagus?

    <p>Actively moves food and liquids to the stomach</p> Signup and view all the answers

    What is the approximate length of the esophagus?

    <p>25 cm (10 in.)</p> Signup and view all the answers

    What structures does the esophagus descend posterior to?

    <p>The trachea</p> Signup and view all the answers

    Which of the following describes the layers of the esophageal wall?

    <p>All of the above</p> Signup and view all the answers

    What are the three phases of swallowing?

    <p>Buccal phase, Pharyngeal phase, Esophageal phase</p> Signup and view all the answers

    What is the role of the upper esophageal sphincter?

    <p>Prevents air from entering the esophagus</p> Signup and view all the answers

    What is the typical travel time for a bolus through the esophagus?

    <p>9 seconds</p> Signup and view all the answers

    What is the function of the pyloric sphincter?

    <p>Regulates release of chyme into the duodenum</p> Signup and view all the answers

    Which cells secrete hydrochloric acid in the stomach?

    <p>Parietal cells</p> Signup and view all the answers

    What is the function of intrinsic factor?

    <p>Aids in vitamin B12 absorption</p> Signup and view all the answers

    What are circular folds in the small intestine?

    <p>Series of transverse folds along the intestinal lining that increase surface area for absorption.</p> Signup and view all the answers

    What are intestinal villi?

    <p>Fingerlike projections of mucosa covered by epithelial cells.</p> Signup and view all the answers

    What role do Paneth cells play in the intestines?

    <p>They have a role in innate immunity and release defensins and lysozyme.</p> Signup and view all the answers

    What is the average length of the small intestine?

    <p>6 m (19.7 ft)</p> Signup and view all the answers

    Which segments make up the small intestine?

    <p>Jejunum</p> Signup and view all the answers

    What is the primary function of the duodenum?

    <p>To neutralize acidic chyme.</p> Signup and view all the answers

    What is the total length of the large intestine?

    <p>~1.5 m (4.9 ft)</p> Signup and view all the answers

    Which structures are included in the segments of the large intestine?

    <p>Rectum</p> Signup and view all the answers

    What is the main function of the colon?

    <p>To reabsorb water and compact intestinal contents into feces.</p> Signup and view all the answers

    What are the parts of the colon?

    <p>Transverse colon</p> Signup and view all the answers

    What triggers the urge to defecate?

    <p>Movement of fecal material into the rectum.</p> Signup and view all the answers

    Study Notes

    Tooth Components

    • Dentin: Makes up the majority of a tooth, a mineralized matrix similar to bone but without cells.
    • Pulp Cavity: Inner chamber of the tooth containing blood vessels and nerves.
    • Occlusal Surface: The top surface of the crown used for chewing, crushing, and slicing.
    • Enamel: Hardest biologically manufactured substance, covers the dentin of the crown, composed of calcium phosphate (requires calcium, phosphate, and vitamin D for formation and decay resistance).
    • Gingival Sulcus: Shallow groove around the base of the tooth's neck, epithelial attachment prevents bacteria from entering deeper tissues.
    • Cement: Covers the dentin in the root, less resistant to erosion than dentin.
    • Periodontal Ligament: Creates gomphosis articulation between root dentin and alveolar bone.
    • Root Canal: Narrow tunnel within the tooth's root, passageway for blood vessels and nerves to the pulp cavity, opens into the root canal via the apical foramen.
    • Crown: Portion of the tooth visible in the mouth, projects above the gum line.
    • Neck: Boundary between the crown and root.
    • Root: Portion of the tooth embedded within the gum, sits in a bony tooth socket called an alveolus.

    Types of Teeth

    • Incisors: Blade-shaped, single root, located at the front of the mouth, used for clipping and cutting.
    • Canines (Cuspids): Conical with a sharp ridgeline and pointed tip, single root, used for tearing and slashing.
    • Premolars (Bicuspids): Flattened crowns with prominent ridges, one to two roots, used for crushing, mashing, and grinding.
    • Molars: Very large flattened crowns with prominent ridges, typically three roots (upper jaw) or two roots (lower jaw), adapted for crushing and grinding.

    Tooth Development

    • Deciduous Teeth (Primary, Milk, Baby Teeth): Formed during embryonic development, usually 20 teeth by the age of 2, 5 on each side of the upper and lower jaws: 2 incisors, 1 canine, 2 deciduous molars.
    • Permanent Teeth: Gradually replace deciduous teeth as periodontal ligaments and roots of primary teeth erode. Three additional molars on each side of the upper and lower jaws (third molars = wisdom teeth). 32 total permanent teeth.
    • Impacted Tooth: Fails to erupt due to overcrowding or tilting within the jawbone, most commonly happens with wisdom teeth.

    Oral Cavity Structures

    • Fauces: Space between the oral cavity and oropharynx.
    • Tongue: Manipulates material in the mouth, surface lubricated by secretions from small glands containing water, mucins, and lingual lipase. Attached to the floor of the mouth by the lingual frenulum.
    • Ankyloglossia (Tongue-tie): Frenulum of the tongue is too short, present at birth, interferes with breastfeeding in newborns and speaking in toddlers.

    Myenteric Plexus

    • A network of sensory neurons and autonomic nerve fibers
    • Located between the circular and longitudinal layers of the muscularis externa
    • Works with the submucosal plexus to coordinate local digestive activity

    Mesenteries

    • Suspend the digestive tract within the abdominal cavity
    • Help to prevent the organs from getting tangled
    • Contribute to the movement of the digestive tract
    • Provide a pathway for blood vessels, lymph vessels, and nerves to reach the organs.

    Layers of the Digestive Tract

    • Mucosa: Innermost layer, absorbs nutrients and produces mucus
    • Submucosa: Connective tissue layer containing blood vessels, nerves, lymphatics
    • Muscularis Externa: Smooth muscle responsible for peristalsis and segmentation
    • Serosa: Outermost layer, composed of epithelial tissue and connective tissue

    ### Smooth Muscle

    • Found throughout the body
    • Forms sheets, bundles, or sheaths around tissues
    • Regulates blood flow by surrounding blood vessels
    • Forms ring-shaped sphincters that regulate movement in digestive and urinary tracts
    • In the digestive tract, organized into inner circular and outer longitudinal layers

    Smooth Muscle Cells

    • Relatively long and slender
    • Contain actin and myosin filaments, but arranged differently from skeletal and cardiac muscle
    • Lack T tubules
    • Have a loose network of sarcoplasmic reticulum
    • No myofibrils, sarcomeres, or striations
    • Smooth appearance under a microscope

    Smooth Muscle Cell Contraction

    • Thin filaments are attached to dense bodies which are distributed throughout the sarcoplasm
    • Thick filaments are scattered throughout the sarcoplasm
    • Cell shortens and twists like a corkscrew as it contracts

    Types of Smooth Muscle

    • Multi-unit smooth muscle cells:
      • Innervated in motor units like skeletal muscle, but each cell may connect to more than one motor neuron
      • Found in iris of the eye, portions of the male reproductive system, walls of large arteries, arrector pili muscles of skin
    • Visceral smooth muscle cells:
      • Lack direct connection with motor neurons
      • Arranged in sheets or layers
      • Electrically connected by gap junctions and mechanically connected by dense bodies, contract as a single unit
      • Stimulation can be neural, hormonal, or chemical, pacesetter cells stimulate rhythmic contractions
      • Found in digestive tract walls, gallbladder, urinary bladder, and other internal organs

    Tooth Components

    • Enamel: Hardest substance in the body, covers the crown
    • Dentin: Hard, bone-like tissue located beneath enamel
    • Pulp: Contains blood vessels, nerves, and connective tissue
    • Gingival sulcus: Shallow groove surrounding the base of the neck
    • Cementum: Covers the dentin in the root, less resistant to erosion than dentin
    • Periodontal ligament: Connects root dentin to alveolar bone
    • Root canal: Narrow tunnel within the root of the tooth, passageway for blood vessels and nerves to the pulp cavity
    • Apical foramen: Opening into the root canal

    Tooth Regions

    • Crown: Portion projecting into the oral cavity from the surface of the gums
    • Neck: Boundary between the crown and root
    • Root: Portion below the gum line, sits in a bony tooth socket called an alveolus

    Tooth Types

    • Incisors: Blade-shaped teeth with a single root, located at the front of the mouth, used for clipping or cutting
    • Canines: Conical with a sharp ridgeline and pointed tip, used for tearing or slashing, have a single root
    • Premolars: Have flattened crowns with prominent ridges, used for crushing, mashing, or grinding, have one or two roots
    • Molars: Very large flattened crowns with prominent ridges, adapted for crushing and grinding, typically have three roots (upper jaw) or two roots (lower jaw)

    Tooth Sets

    • Deciduous Teeth: Also known as primary teeth, milk teeth, or baby teeth, 20 deciduous teeth present at age 2
    • Permanent Teeth: Gradually replace deciduous teeth, three additional molars appear on each side of the upper and lower jaws, 32 permanent teeth in total

    Impacted Tooth

    • Fails to erupt due to crowding from adjacent teeth or twisting and tilting within jaw bone
    • Most commonly happens with wisdom teeth
    • Treatment ranges from nothing to tooth extraction

    ### Swallowing

    • Buccal Phase: Voluntary, bolus of food is moved to the back of the mouth
    • Pharyngeal Phase: Involuntary, soft palate elevates and uvula blocks the nasopharynx; epiglottis covers the opening to the larynx; bolus is moved down the pharynx
    • Esophageal Phase: Involuntary, bolus is transported down the esophagus by peristalsis

    Peristalsis

    • Wave-like muscle contractions that move food through the digestive tract
    • More efficient in propelling intestinal contents than segmentation

    Segmentation

    • Rhythmic contractions that mix and churn food in the small intestine

    Enteroendocrine Cells

    • Located in the lining of the digestive tract
    • Secrete hormones that regulate digestion

    Digestive Hormones

    • Gastrin: Stimulates secretion of gastric juice and motility
    • Cholecystokinin (CCK): Stimulates release of bile from gallbladder and pancreatic enzymes
    • Secretin: Stimulates secretion of bicarbonate from pancreas and bile from liver
    • Ghrelin: Stimulates hunger
    • Leptin: Suppresses hunger

    ### Regulation of Gastric Activity

    • Central Mechanisms: Controlled by the autonomic nervous system and hormones
    • Local Mechanisms: Controlled by the presence of food in the stomach and by the release of gastrin and other local hormones

    ### Large Intestine Segments

    • Cecum: First part of the large intestine
    • Colon: Longest part of the large intestine, divided into ascending, transverse, descending, and sigmoid
    • Rectum: Final segment of the large intestine

    ### Large Intestine Role in Fecal Compaction

    • Absorbs water and electrolytes
    • Compacts the waste material into feces
    • Defecation reflex is triggered when feces enter the rectum

    Mesentery

    • Double layer of peritoneal membrane
      • Areolar tissue between layers
        • Provides access for blood vessels, nerves, and lymphatics
      • Stabilizes the organs it connects
      • Prevents entanglement of the intestines

    Digestive Tract Layers

    • Four major layers:
      • Mucosa (inner lining): mucous membrane of epithelium, moistened by glandular secretions and lamina propria of areolar tissue
      • Submucosa: Layer of dense irregular connective tissue
        • Contains blood vessels and lymphatic vessels
        • Also contains exocrine glands in some regions
          • Secrete buffers and enzymes into the digestive tract
      • Muscular layer: Smooth muscle in two layers
        • Inner circular layer
        • Outer longitudinal layer
        • Involved in mechanical processing and movement of materials along the tract
      • Serosa: Layer of visceral peritoneum along the digestive tract within the abdominal cavity
        • No serosa in oral cavity, pharynx, esophagus, and rectum
          • Covered by adventitia (dense collagen fiber sheath)
          • Firmly attaches tract to adjacent structures

    Digestive Regulation

    • Local factors:
      • Primary stimulus for digestive activities
      • Examples:
        • Changes in pH of lumen contents
        • Physical distortion of the digestive tract wall
        • Presence of specific nutrients or chemical messengers from the mucosa
    • Neural Control:
      • Short reflexes (myenteric reflexes): Triggered by chemoreceptors or stretch receptors in digestive tract walls
        • Controlling neurons located in the myenteric plexus
      • Long reflexes: Higher level of control involving interneurons and motor neurons of the CNS
        • Control large-scale peristalsis, moving material along the tract
        • May involve parasympathetic motor fibers that synapse in the myenteric plexus
    • Hormonal control:
      • Involves at least 18 hormones that affect digestive function
      • Some affect other systems as well
      • Hormones are peptides produced by enteroendocrine cells (endocrine cells in the epithelium of the digestive tract)

    Congenital Megacolon (Hirschsprung Disease)

    • Characterized by absence or reduction of ganglion cells in the myenteric plexus of the rectum
    • Causes paralysis of smooth muscle (no peristaltic movement)
      • Abnormal dilation and hypertrophy of the colon
      • Chronic constipation, bloating, and abdominal pain

    Stomach Wall and Functions

    • Chief cells secrete:
      • Pepsinogen
        • Activated by HCl to become pepsin
          • Active proteolytic (protein-digesting) enzyme
      • Newborns also produce rennin and gastric lipase
        • Important for milk digestion
    • HCl production:
      • Parietal cells do not create HCl in their cytoplasm
        • H+ and Cl- are transported and secreted separately
      • H+ is generated by carbonic anhydrase converting CO2 and H2O to carbonic acid
        • Carbonic acid dissociates into bicarbonate ions and hydrogen ions
      • Bicarbonate ejected into interstitial fluid in exchange for a chloride ion
        • Bicarbonate enters the bloodstream
          • If gastric glands are very active, the amount of bicarbonate released can increase blood pH
          • Sudden influx of bicarbonate ions is called the alkaline tide
      • Chloride ions diffuse across the cell and exit into the lumen of the gastric gland
      • Hydrogen ions are actively transported into the gastric gland lumen

    Hormones Regulating Digestion

    • Multiple hormones regulate digestive activities
      • Many produced by the duodenum
      • Duodenum coordinates gastric activity and digestive secretion based on the characteristics of arriving chyme

    Phases of Gastric Secretion

    • Cephalic phase:
      • Begins when you see, smell, taste, or think of food
      • Directed by the CNS to prepare the stomach
      • Parasympathetic impulse travels down the vagus nerve, stimulating the submucosal plexus
        • Postganglionic fibers innervate gastric gland cells
      • Gastric juice production increases (~500 mL/h)
      • Phase generally lasts minutes
    • Gastric phase:
      • Begins when food arrives in the stomach
      • Stimuli include:
        • Distention of the stomach
        • Increase in gastric content pH
        • Presence of undigested proteins
        • Release of gastrin by G cells in the stomach
        • Gastrin stimulates parietal and chief cells to increase activity
        • Gastric juice production increases significantly
    • Intestinal phase:
      • Begins when chyme enters the duodenum
      • Stimuli include:
        • Distention of the duodenum
        • Presence of acidic chyme
        • Presence of fats and proteins
        • Release of hormones like secretin, cholecystokinin (CCK), and gastric inhibitory peptide (GIP)
        • Secretin stimulates the pancreas to secrete pancreatic fluids containing bicarbonate ions
          • Neutralizes acidic chyme
        • CCK stimulates pancreas to release digestive enzymes and gall bladder to release bile
          • Aids in fat digestion
        • GIP inhibits gastric emptying and slows down gastric secretion
      • Overall effect is to reduce gastric activity and shift focus to intestinal digestion

    Large Intestine

    • Lacks villi
    • Contains distinctive intestinal glands
      • Dominated by mucin-secreting goblet cells
        • Lubricates feces as it becomes drier and more compact
    • Mucosa does not produce enzymes

    Rectum

    • Anal canal (distal portion of rectum): Contains small longitudinal folds called anal columns
      • Epithelium transitions from columnar to stratified squamous epithelium
      • Network of veins in lamina propria and submucosa
        • Increased venous pressure can distend the veins, producing hemorrhoids
          • Increased pressure caused by pregnancy or straining during defecation
    • Internal anal sphincter: Inner circular smooth muscle layer
      • Not under voluntary control
    • External anal sphincter:
      • Outer skeletal muscle layer
      • Under voluntary control
    • Anus:
      • Exit of the anal canal
      • Epidermis becomes keratinized

    Absorption in the Large Intestine

    • Accounts for:
      • Absorption of water and electrolytes
      • Fermentation of indigestible carbohydrates by bacteria
        • Produces short-chain fatty acids, which are absorbed and used as energy
      • Formation and compaction of feces

    Smooth Muscle in the Digestive Tract

    • Smooth muscle in the digestive tract can function over a wide range of lengths, this is referred to as plasticity. This is due to the scattered arrangement of thick and thin filaments in the muscle.
    • Smooth muscle has a normal background activity and tension, called smooth muscle tone. This is caused by various stimulations.

    Smooth Muscle Contractions

    • Peristalsis is a wave of muscle contraction that propels food along the digestive tract.
      • Circular muscles contract behind the bolus as the bolus moves along the tract, longitudinal muscles contract ahead of the bolus and the process continues, propelling the bolus forward.
    • Segmentation is a cycle of contraction and relaxation that churns and fragments the bolus, mixing the contents with intestinal secretions.
      • This occurs in most areas of the small intestine and portions of the large intestine.

    Oral Cavity Boundaries

    • The posterior boundary of the oral cavity includes the root of the tongue and the lingual tonsils.
    • The inferior boundary of the oral cavity includes the body of the tongue, the geniohyoid and mylohyoid muscles.

    Oral Cavity Structures

    • The oral vestibule is the space between the cheeks or lips and teeth.
    • The frenulum of the upper lip attaches the gums to the upper lip.
    • The frenulum of the lower lip attaches the gums to the lower lip.
    • The palatal arches are on either side of the uvula and connect the soft palate.
      • The palatoglossal arch connects the soft palate to the base of the tongue.
      • The palatopharyngeal arch connects the soft palate to the pharyngeal wall.

    Peritoneal Cavity

    • The peritoneal cavity encloses the stomach and most of the intestine.
    • It is lined by the peritoneum, which forms the serosa or visceral peritoneum covering the organs enclosed by the cavity, and the parietal peritoneum lining the inner surface of the peritoneal cavity.

    Mesenteries

    • The peritoneal cavity secretes peritoneal fluid into the peritoneal cavity at a rate of about 7 liters per day. This fluid is reabsorbed and the volume at any one time is about 50 mL.

    Large Intestine Segments

    • The ascending colon moves from the cecum up the right side of the peritoneal cavity to the inferior surface of the liver, where it bends to the left forming the right colic flexure.
    • The transverse colon crosses the abdomen from right to left, supported by the transverse mesocolon. It bends at 90 degrees to the left forming the left colic flexure.
    • The descending colon moves inferiorly along the body’s left side to the iliac fossa, ending at the sigmoid flexure.
    • The sigmoid colon is an S-shaped segment about 15 cm long that empties into the rectum.

    Large Intestine Wall

    • The large intestine wall lacks villi but has intestinal glands dominated by mucin-secreting goblet cells which lubricate feces. The mucosa of the large intestine does not produce enzymes.

    The Rectum

    • The anal canal, the distal portion of the rectum, has small longitudinal folds called anal columns.
    • The epithelium of the anal canal transitions from columnar to stratified squamous.
    • Increased venous pressure can distend veins in the lamina propria and submucosa causing hemorrhoids, often caused by pregnancy or straining during defecation.
    • The internal anal sphincter is the inner circular smooth muscle layer, not under voluntary control.
    • The external anal sphincter is the outer skeletal muscle layer, under voluntary control.
    • The anus is the exit of the anal canal, where the epidermis becomes keratinized.

    The Digestive System

    • The system is composed of the major organs: the mouth, pharynx, esophagus, stomach, small intestine, and large intestine.
    • It also includes accessory organs: the teeth, tongue, salivary glands, liver, gallbladder, and pancreas.

    Digestive Tract Functional Histology

    • Four layers:
      • Mucosa: the inner lining, which faces the lumen. It is responsible for absorption, secretion, and protection.
      • Submucosa: a layer of connective tissue that provides support and contains blood vessels, lymphatic vessels, and nerves.
      • Muscularis externa: a layer of smooth muscle that is responsible for peristalsis.
      • Serosa (or adventitia): the outermost layer, which is made up of epithelial tissue that reduces friction.

    Smooth Muscle Tissue

    • Composed of elongated spindle-shaped cells.
    • Lack striations.
    • Found in walls of hollow organs like the digestive tract and blood vessels.
    • Able to contract slowly over a sustained period.

    Movement of Materials in the Digestive Tract

    • Peristalsis: Wave-like contractions of smooth muscles that move materials through the digestive tract.
    • Segmentation: Contractions in localized regions that mix the contents of the digestive tract.

    Digestive Regulation Mechanisms

    • Local factors: Changes in pH, physical distortion of the digestive tract, and the presence of chemicals.
    • Neural control mechanisms:
      • Short reflexes: Triggered by receptors in the digestive tract, control local areas of the tract.
      • Long reflexes: Involve the central nervous system and control large-scale movements.
    • Hormonal control mechanisms: Hormones produced by enteroendocrine cells regulate digestive functions.

    Congenital Megacolon (Hirschsprung Disease)

    • Caused by the absence or reduction of ganglion cells in the myenteric plexus of the rectum.
    • Results in paralysis of the smooth muscle, leading to abnormal colon dilation and hypertrophy.
    • Symptoms include chronic constipation, bloating, and abdominal pain.

    Gastric Phase

    • Begins when proteins and peptides are present in the stomach.
    • Gastrin secretion increases stomach mixing movements and further secretion.
    • Lasts for 3-4 hours.

    Intestinal Phase

    • Begins when chyme enters the duodenum.
    • Distention of the duodenum initiates the enterogastric reflex, which inhibits gastrin production, decreases gastric motility and secretion, and stimulates the contraction of the pyloric sphincter.
    • Mucus production increases in the duodenum.

    Gastric Central Reflexes

    • Triggered by stimulation of stretch receptors in the stomach.
    • Accelerate movements along the small intestine.
    • The rate of chyme movement into the small intestine is fastest when the stomach is greatly distended.

    The Large Intestine

    • ~1.5 m long, ~7.5 cm in diameter.
    • Functions: reabsorbing water, absorbing vitamins, and storing fecal material.
    • Segments: cecum, colon, and rectum.

    Cecum

    • An expanded pouch that collects and stores material from the small intestine.
    • Begins the process of compaction.
    • Contains the ileocecal valve, controlling the movement of material from the small intestine into the cecum.
    • Attached to the appendix, which contains numerous lymphoid nodules and functions as a part of the immune system.

    Colon

    • Four sections: ascending, transverse, descending, and sigmoid.
    • Thicker wall than the small intestine.
    • Responsible for further absorption of water and electrolytes and waste compaction.

    Appendix

    • Small finger-like pouch extending.
    • Contains lymph tissue, aiding in immune system function.
    • Inflammation of the appendix is called appendicitis.

    Rectum

    • The final segment of the large intestine.
    • Stores fecal material before defecation.

    Defecation

    • The process of eliminating feces.
    • Controlled by the internal and external anal sphincters.
    • Internal anal sphincter is involuntary, and relaxes upon rectal distention.
    • External anal sphincter is voluntary, and allows control over defecation.

    Nerve Plexuses

    • Myenteric plexus is located in the muscularis externa, between the circular and longitudinal layers.
    • Myenteric plexus is a network of sensory neurons and autonomic nerve fibers.
    • The myenteric and submucosal plexus work together to control digestive activity.

    Mesenteries

    • They are important for suspending the digestive tract and stabilizing its position.
    • They also provide a route for blood vessels, nerves and lymphatic vessels.

    Digestive Tract Layers

    • Lumen: The space inside the digestive tract, through which food passes.
    • Mucosa: Innermost layer, which lines the lumen.
    • Submucosa: Connective tissue layer containing blood vessels, nerves, and lymphatic vessels.
    • Muscularis externa: Smooth muscle responsible for the churning and movement of food.
    • Serosa: Outermost layer, which is a thin layer of connective tissue.

    Submucosal Plexus vs. Myenteric Plexus

    • Submucosal plexus controls secretions and local blood flow.
    • Myenteric plexus is responsible for controlling motility and movement of food.

    Smooth Muscle

    • Found throughout the body.
    • Forms sheets, bundles, or sheaths around tissues like blood vessels and hollow organs.
    • Regulates blood flow in blood vessels.
    • Forms ring-shaped sphincters that regulate movement along passageways in the digestive and urinary systems.

    Digestive Tract Smooth Muscle

    • Organized into inner circular layer and outer longitudinal layer.
    • Cells in each layer are aligned parallel to each other.

    Smooth Muscle Cells

    • Long and slender, with diameters ranging from 5–10 µm and lengths ranging from 30–200 µm.
    • Contain actin and myosin filaments, but their organization differs from skeletal and cardiac muscle.
    • Contain no T tubules.
    • Sarcoplasmic reticulum forms a loose network throughout the sarcoplasm.
    • Have no myofibrils or sarcomeres.
    • Lack of striations gives the tissue a smooth microscopic appearance.

    Digestive Tract

    • Around 10 m (33 ft) long muscular tube.

    Major Digestive Organs & Functions

    • Oral cavity (mouth): Mechanical processing of food with teeth and tongue, moistening, mixing with salivary secretions.
    • Pharynx: Muscular propulsion of food into the esophagus.
    • Esophagus: Transport of materials to the stomach.
    • Stomach: Chemical breakdown and mechanical processing of food.
    • Small intestine: Enzymatic digestion and absorption of nutrients.
    • Large intestine: Dehydration and compaction of indigestible materials.

    Digestive Tract Functions

    • Ingestion: Taking in solid food and liquid into the oral cavity.
    • Mechanical Digestion & Propulsion: Crushing and shredding food in the oral cavity, mixing and churning in the stomach.
    • Chemical Digestion: Breakdown of food into smaller molecules by enzymes.
    • Secretion: Release of water, acids, enzymes, buffers, and salts by digestive organs.
    • Absorption: Movement of nutrients across the digestive epithelium into the bloodstream.
    • Defecation: Elimination of indigestible food compacted into feces.

    Teeth Components

    • Enamel: Outermost layer of the tooth, hard and resistant to abrasion.
    • Dentin: Layer beneath enamel, harder than bone, but less resistant to abrasion.
    • Pulp: Innermost part of the tooth containing blood vessels, nerves, and connective tissue.
    • Gingival Sulcus: Shallow groove surrounding the base of the tooth, preventing bacteria from accessing deeper tissues.
    • Cement: Covers the dentin in the root, less resistant to erosion than dentin.
    • Periodontal ligament: Connects the root dentin to the alveolar bone, creating a gomphosis joint.
    • Root canal: Narrow tunnel within the root of the tooth, containing blood vessels and nerves.
    • Apical Foramen: Opening into the root canal.

    Teeth Regions

    • Crown: Portion projecting into the oral cavity from the surface of the gums.
    • Neck: Boundary between the crown and root.
    • Root: Portion below the gum line, embedded in the alveolus.

    Tooth Types

    • Incisors: Front teeth, blade-shaped with a single root, used for clipping or cutting.
    • Canines: Conical teeth with a sharp ridgeline and pointed tip, used for tearing or slashing, with a single root.
    • Premolars: Flattened crowns with prominent ridges, used for crushing and grinding, with one or two roots.
    • Molars: Large teeth with broad crowns and multiple cusps, used for grinding, with three or more roots.

    Intestinal Tract Structures

    • Circular folds (plicae circulares): Transverse folds along the intestinal lining, permanent structures, mostly in the jejunum.
    • Intestinal villi: Fingerlike projections of mucosa, covered by epithelial cells with microvilli.
    • Intestinal glands: Located at the bases of villi, containing stem cells that produce epithelial cells and Paneth cells.
    • Paneth cells: Found at the base of intestinal glands, release defensins and lysozyme for innate immunity.

    Villus Internal Structure

    • Capillary network: Extensive network in the lamina propria, carries absorbed nutrients to the hepatic portal circulation.
    • Lacteal: Lymphatic capillary, transports materials too large to enter blood capillaries, like chylomicrons.

    Large Intestine Segments

    • Cecum: First part of the large intestine, where the small intestine connects, contains the appendix.
    • Colon: Longest part of the large intestine, divided into ascending, transverse, descending, and sigmoid portions.
    • Rectum: Last 15 cm (6 in.) of the digestive tract, expandable for temporary feces storage.

    Large Intestine Structures

    • Omental appendices: Teardrop-shaped sacs of fat in the serosa of the colon.
    • Tenia coli: Three longitudinal bands of smooth muscle, creating haustra.
    • Haustra: Pouches in the colon wall created by the tenia coli, allowing for expansion and elongation.

    Large Intestine Function

    • Absorption of water and electrolytes: Absorbs most of the remaining water and electrolytes from indigestible food.
    • Compaction of waste: Compacts indigestible materials into feces.
    • Production of vitamin K: Contains bacteria that synthesize vitamin K.
    • Storage and elimination of feces: Holds feces until defecation.

    Mass Movements

    • Powerful peristaltic contractions that occur a few times daily.
    • Initiated by distension of the stomach and duodenum.
    • Begin at the transverse colon and push materials along the distal portion of the large intestine.

    The Pharynx

    • It is a membrane-lined cavity posterior to the nose and mouth.
    • It is continuous with the esophagus.
    • It is a common passageway for air, food, and liquids.
    • It has three regions: nasopharynx, oropharynx, and laryngopharynx.

    The Esophagus

    • It is a hollow, muscular tube roughly 25 cm (10 inches) long and 2 cm (0.8 inches) wide.
    • Its narrowest point is at the beginning, posterior to the cricoid cartilage.
    • It descends posterior to the trachea.
    • It enters the abdominopelvic cavity through the esophageal hiatus, an opening in the diaphragm.
    • Its muscles maintain resting muscle tone, keeping the lumen closed except during swallowing.
    • It is innervated by parasympathetic and sympathetic fibers from the esophageal plexus.
    • It has two sphincters: the upper esophageal sphincter and the lower esophageal sphincter (cardiac sphincter).
    • The upper esophageal sphincter prevents air from entering the esophagus.
    • The lower esophageal sphincter prevents backflow of stomach contents.

    The Small Intestine

    • It plays a key role in nutrient digestion and absorption.
    • It absorbs 90% of nutrients, with the remaining 10% absorbed in the large intestine.
    • Its average overall length is 6 m (19.7 feet) with a diameter that ranges from 4 cm (1.6 inches) near the stomach to 2.5 cm (1 inch) near the large intestine.
    • It has three segments: the duodenum, jejunum, and ileum.

    The Duodenum

    • It is 25 cm (10 inches) in length.
    • It's the segment closest to the stomach.
    • It acts as a mixing bowl for chyme from the stomach and digestive secretions from the liver, gallbladder, and pancreas.
    • It is mostly retroperitoneal.
    • It has few circular folds and small vili, it possesses duodenal glands that produce mucus secretions.
    • Its main function is to neutralize acidic chyme.

    Jejunum

    • It is located between the duodenum and ileum.
    • It is marked by a sharp bend at its beginning.
    • It is about 2.5m (8.2 feet) in length.
    • It is found within the peritoneal cavity.
    • It has numerous circular folds and abundant long villi.
    • It is where the majority of chemical digestion and nutrient absorption occur.

    Ileum

    • It is the final segment of the small intestine.
    • It is about 3.5 m (11.5 feet) in length, ending at the ileocecal valve.
    • The ileocecal valve is a sphincter that controls the flow from the ileum into the cecum of the large intestine.
    • It has few circular folds, none in the distal portion.
    • It has relatively stumpy villi.
    • Its submucosa contains aggregated lymphoid nodules.

    Intestinal Tract Structures

    • Circular folds: These transverse folds along the intestinal lining are permanent features, increasing surface area for absorption.
    • Intestinal villi: They are fingerlike projections of mucosa, covered with epithelial cells whose surfaces are covered with microvilli.
    • Intestinal glands: They are located at the base of villi.
    • Microvilli: They act as a carpet on epithelial cell surfaces, dramatically increasing the surface area for absorption. They also house enzymes responsible for digesting materials.
    • Smooth muscle: Found in the muscularis mucosae and within the villi, it moves the villi back and forth exposing the surfaces to intestinal contents, and squeezes the lacteal, aiding in lymph movement.
    • Lamina propria: It contains an extensive capillary network transporting absorbed nutrients to the hepatic portal circulation.
    • Lacteal: This lymphatic capillary (lacteus, milky) transports materials that cannot enter blood capillaries, like the absorbed fatty acids assembled into protein-lipid packages (chylomicrons) which are too large to diffuse into the bloodstream.

    Gastric Secretion Phases

    • There are three phases: the cephalic phase, the gastric phase, and the intestinal phase.
    • Cephalic phase: This phase is initiated by the thought, smell, sight, and taste of food. It involves increased gastric motility (mixing waves) and secretion by parietal and chief cells.
    • Gastric phase: It is triggered by the arrival of food in the stomach and presence of undigested materials (mostly proteins and peptides) in the stomach; stimulates gastrin secretion, increasing gastric motility and secretion by parietal and chief cells.
    • Intestinal phase: It begins when chyme enters the duodenum, typically after several hours of mixing. It initiates the enterogastric reflex, which inhibits gastrin production, decreases gastric motility and secretion, and stimulates contraction of the pyloric sphincter, decreasing chyme release into the duodenum. Mucus production is increased in the duodenum.

    The Pharynx

    • The pharynx, commonly known as the throat, is a membrane-lined cavity located posterior to the nose and mouth.
    • It is continuous with the esophagus and acts as a common passageway for air, liquids, and solid food.
    • It can be divided into three regions:
      • Nasopharynx
      • Oropharynx
      • Laryngopharynx

    The Esophagus

    • The esophagus is a hollow, muscular tube about 25 cm long and 2 cm wide.
    • It functions to actively move food and liquids to the stomach.
    • The esophagus has the narrowest point at its beginning, located posterior to the cricoid cartilage.
    • It descends posterior to the trachea and enters the abdominopelvic cavity through the esophageal hiatus.
    • The esophagus is innervated by parasympathetic and sympathetic fibers from the esophageal plexus, which maintain resting muscle tone in the circular muscle layer. This keeps the lumen closed except during swallowing.

    Esophageal Sphincters

    • The esophagus features two sphincters:
      • The upper esophageal sphincter is a band of smooth muscle that functions as a sphincter to prevent air from entering the esophagus.
      • The lower esophageal sphincter (cardiac sphincter) is located at the inferior end of the esophagus and is normally contracted to prevent backflow of stomach contents.

    Layers of the Esophageal Wall

    • The esophageal wall consists of four layers:
      • The mucosa, composed of non-keratinized stratified squamous epithelium, and the submucosa form large folds that extend the length of the esophagus, allowing for expansion when a bolus passes.
      • The muscularis externa, composed of skeletal muscle in its superior third, a mix of skeletal and smooth muscle in its middle third, and smooth muscle in its inferior third.
      • It lacks a serosa and instead has an adventitia of connective tissue, which anchors the esophagus to the posterior body wall.

    The Process of Swallowing

    • Swallowing, also known as deglutition, is a complex process that starts voluntarily but proceeds automatically. It involves three phases.
      • The buccal phase is a strictly voluntary phase that begins with compression of the bolus against the hard palate. The tongue forces the bolus into the oropharynx while simultaneously elevating the soft palate to seal off the nasopharynx. Entry into the oropharynx triggers the next phase.
      • The pharyngeal phase begins when the bolus stimulates tactile receptors in the uvula and palatine arches. Motor commands from the swallowing center in the medulla oblongata coordinate muscle contractions in pharyngeal muscles. The larynx elevates, the epiglottis folds, and the uvula and soft palate elevate. The bolus then moves through the pharynx into the esophagus.
      • The esophageal phase starts as the bolus is forced through the entrance of the esophagus. Peristalsis pushes the bolus toward the stomach as the bolus approaches, leading to opening of the lower esophageal sphincter. The bolus then enters the stomach, usually within 9 seconds, with liquids traveling faster. A dry bolus may require secondary peristaltic waves.

    The Peritoneal Cavity

    • The peritoneal cavity encloses the stomach and most of the small intestine.
    • It is lined by a serous membrane called the peritoneum, which can be divided into:
      • Serosa or visceral peritoneum, which covers organs within the peritoneal cavity.
      • Parietal peritoneum, which lines the inner surface of the peritoneal cavity.

    Function of the Peritoneum

    • The peritoneum continuously secretes peritoneal fluid into the peritoneal cavity.
    • About 7 liters/day are secreted & reabsorbed, with approximately 50 mL present at any given time.
    • This thin layer separates the parietal and visceral surfaces, allowing for sliding movements without friction or irritation.
    • Increased fluid accumulation can occur due to issues like liver disease, kidney disease, and heart failure leading to abdominal swelling (ascites).

    Stomach Wall Layers

    • The stomach wall consists of four layers:
      • The mucosa is composed of simple columnar epithelium that produces an alkaline mucus layer protecting epithelial cells from the acid and enzymes in the gastric lumen. Gastric epithelial cells have a short lifespan of 3-7 days.
      • The submucosa, a layer of connective tissue.
      • The muscularis layer, which has three layers: oblique, circular, and longitudinal.
      • The serosa, the outermost layer.

    Gastric Glands

    • Glands in the fundus and body of the stomach secrete most of the acid and enzymes involved in gastric digestion.
    • They are dominated by parietal cells and chief cells.
    • These glands secrete ~1.5 L of gastric juice every day.
    • Glands in the pylorus secrete mucus and hormones that coordinate and control digestive activity.

    Gastric Pits

    • Gastric pits are shallow depressions that open onto the gastric surface.
    • Active stem cells in the base of each pit replace superficial cells shed into the chyme.
    • Each gastric pit connects to several gastric glands.

    Cells of Gastric Glands

    • Parietal cells secrete:
      • Intrinsic factor, a glycoprotein that helps in vitamin B12 absorption.
      • Hydrochloric acid (HCl), which activates pepsinogen and maintains a stomach pH between 1.5-2.
    • G cells, a type of enteroendocrine cell, produces various hormones.

    ### Esophagus

    • Esophagus is a muscular tube that connects the pharynx to the stomach
    • It's about 25 cm (10 in) long
    • It has four layers of tissue: mucosa, submucosa, muscularis externa, and adventitia
    • Mucosa is nonkeratinized stratified squamous epithelium
    • This allows for expansion with the passage of a bolus
    • Muscularis externa is made up of skeletal muscle in the superior third, a mix of skeletal and smooth muscle in the middle third, and smooth muscle in the inferior third
    • This allows peristalsis to occur
    • Adventitia anchors the esophagus to the posterior body wall

    Swallowing

    • Swallowing, also known as deglutition, starts as a voluntary process that becomes involuntary
    • Three phases of swallowing:
    • Buccal phase: is strictly voluntary
    • Begins with compression of the bolus against the hard palate
    • Tongue forces the bolus into the oropharynx, while elevating the soft palate to seal off the nasopharynx
    • Entry into the oropharynx triggers the pharyngeal phase reflex
    • Pharyngeal phase: begins when tactile receptors in the uvula and the palatine arches are stimulated
    • Motor commands from the swallowing center in the medulla oblongata coordinate muscle contraction in pharyngeal muscles
    • Larynx is elevated. The epiglottis is folded. The uvula and soft palate are elevated
    • The bolus is moved from the pharynx into the esophagus
    • Esophageal phase:
    • The bolus travels through the esophagus via peristalsis

    Teeth

    • Two sets of teeth:
    • Deciduous teeth: also known as primary teeth, milk teeth, or baby teeth
    • 20 deciduous teeth by age 2
    • 5 teeth are on each side of the upper and lower jaw
    • 2 incisors, 1 canine, 2 deciduous molars
    • Permanent teeth: gradually replace the deciduous teeth
    • Periodontal ligaments and roots of primary teeth erode, causing the primary teeth to fall out or be pushed aside by the permanent teeth.
    • Three additional molars appear on each side of the upper and lower jaw for a total of 32 permanent teeth
    • The third molars are called wisdom teeth
    • Impacted tooth: a tooth that fails to erupt due to overcrowding or twisting
    • Most common in wisdom teeth
    • Treatments vary from doing nothing to tooth extraction

    Oral Cavity

    • Oral cavity is lined with stratified squamous epithelium
    • This allows for protection against abrasion from chewing
    • Structures of the oral cavity:
    • Fauces: space between the oral cavity and the oropharynx
    • Tongue: manipulates materials inside the mouth
    • The tongue’s surface is flushed by secretions of small glands containing water, mucins, and lingual lipase
    • The tongue is attached to the floor of the mouth by the frenulum of the tongue (lingual frenulum)
    • Ankyloglossia (tongue-tie): present at birth
    • The frenulum of the tongue is too short
    • Interferes with breastfeeding in newborns and learning to speak in toddlers

    ### Components of a Tooth

    • Dentin: the bulk of each tooth is composed of dentin
    • It's a mineralized matrix similar to bone but contains no cells
    • Pulp cavity: The interior chamber of the tooth
    • This chamber is filled with pulp, which contains blood vessels, nerves, and connective tissue
    • Occlusal surface: the portion of the crown used for crushing, slicing, or chewing
    • Enamel: covers the dentin of the crown
    • Hardest biologically manufactured substance composed of calcium phosphate
    • Needs calcium, phosphate, and vitamin D for formation and resistance to decay

    ### Stomach

    • A muscular, expandable, J-shaped organ with three layers in the muscular layer
    • It is a highly variable shape depending on its contents
    • Empty: a muscular tube with a constricted lumen
    • Full: can expand to contain 1–1.5 liters of material (chyme)
    • Chyme is a viscous, highly acidic, soupy mixture formed from the combination of food, saliva, and gastric gland secretions.
    • Lesser curvature forms the medial surface
    • Attached to the mesentery of the lesser omentum
    • Greater curvature forms the lateral and inferior surfaces
    • Attached to the mesentery of the greater omentum
    • Four regions:
    • Fundus: superior to the junction between the stomach and esophagus
    • Cardia: superior and medial part within 3 cm of the gastroesophageal junction
    • It secretes mucus to protect the esophagus from stomach acid and enzymes
    • Body: the largest region between the fundus and pylorus
    • Works as a mixing bowl
    • Pylorus: sharp curve of the “J” of the stomach
    • Frequently changes shape with mixing movements

    Large Intestine

    • Also known as the large bowel
    • Average length of about 1.5 m and a diameter of 7.5 cm
    • Major functions:
    • Reabsorbing water and compacting intestinal contents into feces
    • Absorbing vitamins generated by bacterial action
    • Storing fecal material prior to defecation
    • Three segments: cecum, colon, rectum
    • Segments:
    • Cecum: expanded pouch that collects and stores material
    • Begins the process of compaction
    • Connects to the ileum at the ileocecal valve
    • Appendix: attached to the cecum
    • About 9 cm long
    • Contains numerous lymphoid nodules and functions as a lymphoid organ
    • Appendicitis is inflammation of the appendix
    • Colon: larger diameter and thinner wall than the small intestine
    • Four regions:
    • Ascending colon
    • Transverse colon
    • Descending colon
    • Sigmoid colon

    Digestive Tract Structure

    • Mucosa: The innermost layer composed of:
      • Mucosal Epithelium: Stratified squamous epithelium at the beginning and end of the tract; Simple columnar epithelium with goblet cells in the stomach and intestines
      • Villi: Small projections with surface area for absorption
      • Lamina Propria: Areolar tissue containing blood vessels, nerve endings, lymphatic vessels, smooth muscle, lymphoid tissue, and mucous glands
      • Muscularis Mucosae: Two smooth muscle layers (inner circular and outer longitudinal) that alter lumen shape and move circular folds and villi.

    Nerve Plexuses

    • Submucosal Neural Plexus:
      • Located in the submucosa
      • Innervates the mucosa and submucosa
      • Contains sensory neurons and autonomic nerve fibers
      • Controls local digestive activities
      • Parasympathetic stimulation increases digestive muscle tone and activity
      • Sympathetic stimulation decreases muscle tone and activity

    Oral Cavity Structures

    • Fauces: Space between the oral cavity and oropharynx
    • Tongue: Manipulates food in the mouth with mucous secretions
      • Secretions contain water, mucins, and lingual lipase (an enzyme that begins lipid digestion)
      • Attached to the floor of the mouth by the frenulum of the tongue (lingual frenulum)
    • Ankyloglossia (Tongue-Tie):
      • Present at birth
      • Shortened frenulum
      • Interferes with breastfeeding and speaking

    Tooth Components

    • Dentin: The majority of the tooth structure, composed of a mineralized matrix similar to bone but with no cells
    • Pulp Cavity: The interior chamber of the tooth
    • Occlusal Surface: The crown portion used for crushing, slicing, or chewing
    • Enamel: Covers dentin on the crown and is the hardest biological substance; composed of calcium phosphate, requiring calcium, phosphate, and vitamin D for formation and decay resistance
    • Gingival Sulcus: A shallow groove surrounding the neck base, filled with epithelial attachment to prevent bacteria from accessing the root
    • Cement: Covers dentin on the root, less resistant to erosion than dentin
    • Periodontal Ligament: Creates the attachment between root dentin and alveolar bone
    • Root Canal: A narrow channel in the root for blood vessels and nerves to the pulp cavity
      • The opening to the root canal is the apical foramen

    Tooth Regions

    • Crown: The portion projecting into the oral cavity from the gum surface
    • Neck: Boundary between the crown and root
    • Root: The portion below the gum line, residing in a bony tooth socket called an alveolus

    Tooth Types

    • Each tooth type has a distinct shape and root pattern:
      • Incisors: Blade-shaped teeth with a single root located at the front of the mouth, used for clipping or cutting
      • Canines (Cuspids): Conical with a sharp ridge and pointed tip used for tearing or slashing; have a single root
      • Premolars (Bicuspids): Have flattened crowns with prominent ridges, used for crushing, mashing, or grinding; have one or two roots
      • Molars: Flattened crowns with prominent ridges, used for crushing, mashing, or grinding; have two or three roots

    Digestive System Breakdown

    • The digestive system is responsible for providing nutrients for cell maintenance and growth.
    • It consists of a muscular tube called the digestive tract, also known as the gastrointestinal (GI) tract or alimentary canal.
    • The digestive system supports tissues that have no direct contact with the outside environment.
    • The digestive tract is composed of:
      • Major Organs: mouth, pharynx, esophagus, stomach, small intestine, large intestine, anus
      • Accessory Organs: teeth, tongue, salivary glands, liver, gallbladder, pancreas
    • The digestive tract is a long, muscular tube lined with permanent ridges and temporary folds that increase surface area for nutrient absorption.
    • The digestive tract has four major layers:
      • Mucosa (inner lining): mucous membrane of epithelium, moistened by glandular secretions, and lamina propria of areolar tissue
      • Submucosa: dense irregular connective tissue containing blood vessels, lymphatic vessels, and exocrine glands.
      • Muscular layer: smooth muscle in two layers (inner circular layer and outer longitudinal layer)
      • Serosa: layer of visceral peritoneum along the digestive tract in the abdominal cavity.
    • Nerve plexuses control local digestive activities:
      • Submucosal neural plexus: located in the submucosal layer, innervates the mucosa and submucosa
      • Myenteric plexus: located in the muscularis externa, works with the submucosal plexus to coordinate local control of digestive activity.
    • Smooth muscle tissue is found throughout the body, but it plays a prominent role in the digestive tract:
      • Smooth muscle cells are longer and slender than skeletal muscle cells, contain no T tubules, and lack striations.
      • Smooth muscle contraction relies on the interaction of thin and thick filaments.
    • Two types of smooth muscle:
      • Multi-unit smooth muscle cells: innervated in motor units like skeletal muscle, located in the iris of the eye, portions of the male reproductive system, and walls of large arteries.
      • Visceral smooth muscle cells: lack any direct connection with motor neurons, arranged in sheets or layers, stimulated by neural, hormonal, or chemical signals.
    • Functional Characteristics of Smooth Muscle:
      • Plasticity: ability to function over a wide range of lengths
      • Smooth muscle tone: normal background activity and tension due to various stimulations
    • Smooth muscle contractions produce motility of the digestive tract:
      • Peristalsis: wave of muscle contraction that propels food along the digestive tract.
      • Segmentation: cycles of contraction that churn and fragment food to mix it with intestinal secretions.
    • Digestive regulation mechanisms:
      • Local factors: primary stimulus for digestive activities, examples include changes in pH, physical distortion of the digestive tract wall, and presence of chemicals.
      • Neural control mechanisms:
        • Short reflexes (myenteric reflexes): triggered by chemoreceptors or stretch receptors in digestive tract walls.
        • Long reflexes: higher level of control, may involve parasympathetic motor fibers.
      • Hormonal control mechanisms: involve hormones produced by enteroendocrine cells, which affect digestive function.
    • Congenital megacolon (Hirschsprung disease): characterized by absence or reduction of ganglion cells in the myenteric plexus, causes paralysis of smooth muscle, leading to abnormal dilation and hypertrophy of the colon and chronic constipation.

    Digestive Tract Organs and Functions

    • Oral Cavity: responsible for ingestion, mechanical digestion, and chemical digestion
      • Structures: lips, cheeks, palate, tongue, teeth, salivary glands
      • Lips and cheeks keep food in the mouth, palate separates the oral cavity from the nasal cavity, tongue mixes food, teeth mechanically break down food, and salivary glands secrete saliva, which moistens food, and begins chemical digestion of carbohydrates.
    • Teeth:
      • Types: incisors, canines, premolars, molars
      • Deciduous teeth: 20 primary teeth that erupt between 6 months and 2 years of age
      • Permanent teeth: 32 secondary teeth that replace the deciduous teeth between 6 and 13 years of age.
    • Pharynx: muscular passageway for air and food, plays a crucial role in swallowing.
    • Esophagus: muscular tube that transports food to the stomach, contracts to produce peristaltic waves to move food through the digestive tract.
    • Swallowing (deglutition): complex coordinated process involving the mouth, pharynx, and esophagus.
      • Oral phase: voluntary, beginning with the tongue pushing the bolus of food to the back of the mouth.
      • Pharyngeal phase: involuntary, bolus moves through the pharynx and esophagus.
      • Esophageal phase: involuntary, bolus moves through the esophagus to the stomach.

    Digestive Tract

    • The digestive tract is a muscular tube about 10 meters (33 feet) long.
    • It begins at the mouth (oral cavity) and ends at the anus.
    • The major organs of the digestive tract and their functions include:
      • Oral Cavity (Mouth): Mechanical processing of food with teeth and tongue, moistening, and mixing with salivary secretions.
      • Pharynx: Muscular propulsion of food into the esophagus.
      • Esophagus: Transport of materials to the stomach.
      • Stomach: Chemical breakdown and mechanical processing of food.
      • Small Intestine: Enzymatic digestion and absorption of nutrients.
      • Large Intestine: Dehydration and compaction of indigestible materials.

    Digestive Tract Functions

    • The primary functions of the digestive tract are:
      • Ingestion: The entry of solid food and liquid into the oral cavity.
      • Mechanical Digestion and Propulsion: Crushing and shredding of food in the mouth, mixing and churning in the stomach.
      • Chemical Digestion: Chemical and enzymatic breakdown of food into smaller molecules for absorption.
      • Secretion: Release of water, acids, enzymes, buffers, and salts by the digestive tract epithelium and accessory organs.
      • Absorption: Movement of nutrients across the digestive epithelium into the bloodstream.
      • Defecation: Elimination of compacted indigestible waste material (feces) from the body.

    Oral Cavity

    • The oral cavity is lined by oral mucosa (stratified squamous epithelium) that varies in thickness and keratinization depending on location.
    • Keratinized oral mucosa is found in areas subjected to abrasion (superior tongue surface, hard palate).
    • Non-keratinized oral mucosa is found on cheeks, lips, and the inferior tongue surface, which enables rapid absorption of lipid-soluble drugs (e.g., nitroglycerin).
    • The hard palate forms the roof of the mouth and is made of the palatine processes of the maxillary bones and the horizontal plates of the palatine bones.
    • The soft palate is the muscular region posterior to the hard palate and helps prevent food from entering the pharynx prematurely during swallowing.
    • The uvula, a dangling process extending from the soft palate, also helps prevent food from entering the pharynx prematurely.
    • The palatine tonsils are located on either side of the oropharynx.
    • The root of the tongue is the fixed portion projecting into the oropharynx, marked by a V-shaped line of vallate papillae.
    • The lingual tonsils are located in the root of the tongue.
    • The body of the tongue is the anterior, mobile portion of the tongue.
    • The frenulum of the tongue (lingual frenulum) attaches the tongue to the floor of the mouth.
    • The oral vestibule is the space between the cheeks (or lips) and teeth.
    • The frenulum of the upper lip attaches the gums to the upper lip.
    • The frenulum of the lower lip attaches the gums to the lower lip.
    • Gingivae (gums) are ridges of oral mucosa surrounding the base of each tooth, firmly attached to the periostea of the underlying bone.
    • The palatal arches are located on either side of the uvula:
      • Palatoglossal arch: Extends between the soft palate and the base of the tongue.
      • Palatopharyngeal arch: Extends from the soft palate to the pharyngeal wall.
    • The fauces is the space between the oral cavity and the oropharynx.
    • The tongue manipulates materials inside the mouth and its surface is flushed by secretions containing water, mucins, and lingual lipase (an enzyme that begins the digestion of lipids).

    Ankyloglossia (Tongue-Tie)

    • Ankyloglossia is a condition present at birth where the frenulum of the tongue is too short.
    • It can interfere with breastfeeding in newborns and with learning to speak in toddlers.

    Teeth

    • The bulk of each tooth is composed of dentin, a mineralized matrix similar to bone but containing no cells.
    • The pulp cavity is the interior chamber of the tooth containing blood vessels, nerves, and connective tissue.
    • The occlusal surface is the portion of the crown used for crushing, slicing, or chewing.
    • Enamel covers the dentin of the crown and is the hardest biologically manufactured substance, composed of calcium phosphate.
    • The gingival sulcus is a shallow groove surrounding the base of the neck and its epithelial attachment blocks bacteria from accessing deeper tissues around the root.
    • Cement covers the dentin in the root and is less resistant to erosion than dentin.
    • The periodontal ligament creates a gomphosis articulation between the root dentin and the alveolar bone.
    • The root canal is a narrow tunnel within the root of the tooth providing a passageway for blood vessels and nerves to the pulp cavity. The opening into the root canal is called the apical foramen.
    • The crown is the portion projecting into the oral cavity from the surface of the gums.
    • The neck is the boundary between the crown and root.
    • The root is the portion below the gum line sitting in a bony tooth socket called an alveolus.

    Types of Teeth

    • Incisors: Blade-shaped teeth located at the front of the mouth, used for clipping or cutting.
    • Canines (Cuspids): Conical teeth with a sharp ridgeline and pointed tip, used for tearing or slashing.
    • Premolars (Bicuspids): Flattened crown teeth with prominent ridges, used for crushing, mashing, or grinding.
    • Molars: Very large flattened crown teeth with prominent ridges, adapted for crushing and grinding.

    Tooth Sets

    • Deciduous Teeth (Primary Teeth): Also called milk teeth or baby teeth. There are 20 deciduous teeth at 2 years of age (5 on each side of the upper and lower jaws – 2 incisors, 1 canine, 2 deciduous molars).
    • Permanent Teeth: Gradually replace deciduous teeth as the periodontal ligaments and roots of the primary teeth erode. There are 32 permanent teeth including three additional molars on each side of the upper and lower jaws (the third molars are called wisdom teeth).

    Impacted Tooth

    • An impacted tooth fails to erupt due to overcrowding or twisting and tilting within the jaw bone.
    • Most commonly occurs with wisdom teeth and treatment ranges from nothing to tooth extraction.

    Pharynx

    • The pharynx is a membrane-lined cavity posterior to the nose and mouth, continuous with the esophagus.
    • Common passageway for solid food, liquids, and air.
    • The pharynx has three regions:
      • Nasopharynx
      • Oropharynx
      • Laryngopharynx

    Esophagus

    • The esophagus actively moves food and liquids to the stomach.
    • It is a hollow, muscular tube approximately 25 cm (10 in) long and 2 cm (0.8 in) wide.
    • The narrowest point is at the beginning (posterior to the cricoid cartilage).
    • The esophagus descends posterior to the trachea and enters the abdominopelvic cavity through the esophageal hiatus (opening in the diaphragm).
    • The esophagus is innervated by the parasympathetic and sympathetic fibers from the esophageal plexus, maintaining resting muscle tone in the circular muscle layer, keeping the lumen closed except when swallowing.
    • The upper esophageal sphincter is a band of smooth muscle that functions as a sphincter to prevent air from entering the esophagus.
    • The lower esophageal sphincter (cardiac sphincter) is located at the inferior end of the esophagus and is normally contracted to prevent backflow of stomach contents.

    Esophageal Wall Layers

    • The mucosa (nonkeratinized stratified squamous epithelium) and submucosa form large folds that extend the length of the esophagus, allowing for expansion with passage of a bolus.
    • The muscularis externa is composed of:
      • Superior third: Skeletal muscle.
      • Middle third: Mix of skeletal and smooth muscle.
      • Interior third: Smooth muscle only.
    • The esophagus has no serosa and its adventitia of connective tissue anchors it to the posterior body wall.

    Swallowing (Deglutition)

    • Swallowing is initiated voluntarily but proceeds automatically and consists of three phases:
      • Buccal Phase (strictly voluntary): Begins with compression of the bolus against the hard palate, the tongue forces the bolus into the oropharynx, and the soft palate elevates sealing off the nasopharynx. Entry into the oropharynx triggers a reflex response.
      • Pharyngeal Phase: Begins with stimulation of tactile receptors in the uvula and palatine arches. Motor commands from the swallowing center (in the medulla oblongata) coordinate muscle contraction in pharyngeal muscles, elevating the larynx, folding the epiglottis, and elevating the uvula and soft palate. The bolus is moved through the pharynx into the esophagus.
      • Esophageal Phase:
        • Begins as the bolus enters the esophagus, triggering peristaltic waves of muscle contractions that propel the bolus towards the stomach.
        • The upper esophageal sphincter relaxes, allowing the bolus to enter the esophagus.
        • Peristalsis moves the bolus through the esophagus, with pressure behind pushing the bolus along.
        • As the bolus approaches the stomach, the lower esophageal sphincter relaxes to allow passage into the stomach.
        • The sphincter closes again to prevent reflux of stomach contents.

    Ileum

    • The ileum is the final segment of the small intestine.
    • It is approximately 3.5 meters (11.5 feet) in length.
    • The ileum ends at the ileocecal valve, a sphincter controlling the flow from the ileum into the cecum of the large intestine.
    • It has few circular folds, especially in the distal portion.
    • Villi in the ileum are relatively stumpy.
    • The submucosa of the ileum contains aggregated lymphoid nodules.

    Segments of the Small Intestine

    • The three segments of the small intestine from proximal to distal are the duodenum, jejunum, and ileum.
    • The duodenum is located within the epigastric region.

    Functions of the Duodenum

    • The primary function of the duodenum is to receive chyme from the stomach and mix it with digestive secretions from the pancreas, liver, and gall bladder.

    Hormones of the Duodenum

    • The duodenum produces several hormones that regulate digestive activities.
    • These hormones coordinate gastric activity and digestive secretion based on the characteristics of the arriving chyme.

    Major Hormones

    • The major hormones that regulate digestive activities are:
      • Gastrin
      • Secretin
      • Cholecystokinin (CCK)

    Gastric Secretion Phases

    • Gastric secretion occurs in three phases:
      • Cephalic phase: Initiated by sight, smell, taste, or thought of food, stimulates gastric juice production.
      • Gastric phase: Stimulated by food arriving in the stomach, increases gastric juice secretion and muscle contractions.
      • Intestinal phase: Begins when chyme enters the duodenum, inhibits gastrin production and gastric motility, and stimulates pyloric sphincter contraction.

    Central Reflexes

    • Stimulation of stretch receptors in the stomach wall triggers central reflexes, accelerating movements along the small intestine.
    • The rate of chyme movement into the small intestine is fastest when the stomach is greatly distended.

    The Large Intestine

    • The large intestine, also known as the large bowel, is approximately 1.5 meters (4.9 feet) long.
    • The large intestine has a diameter of 7.5 cm (3 in.).
    • Its major functions include:
      • Reabsorbing water and compacting intestinal contents into feces.
      • Absorbing important vitamins generated by bacterial action.
      • Storing fecal material prior to defecation.

    Large Intestine Segments

    • The large intestine consists of three segments:
      • Cecum: An expanded pouch that collects and stores material, beginning the compaction process. It contains the ileocecal valve, which controls the flow from the ileum into the cecum.
      • Colon: Divided into four regions: ascending colon, transverse colon, descending colon, and sigmoid colon.
      • Rectum: The final 15 cm (6 inches) of the digestive tract, stores feces temporarily.

    Cecum

    • The cecum is attached to the appendix, a small, worm-like structure containing numerous lymphoid nodules.
    • Appendicitis is inflammation of the appendix.

    Colon

    • The colon has a larger diameter and thinner wall than the small intestine.
    • The ascending and descending colon are retroperitoneal, while the transverse and sigmoid colon are suspended by remnants of the embryonic mesocolon.

    Mass Movements

    • Mass movements are powerful peristaltic contractions occurring a few times each day, propelled by distension of the stomach and duodenum.
    • These contractions begin at the transverse colon and push materials along the distal portion of the large intestine.

    Large Intestine Wall

    • The large intestine lacks villi.
    • It contains intestinal glands dominated by mucin-secreting goblet cells, which lubricate feces.
    • The mucosa of the large intestine does not produce enzymes.

    Rectum

    • The anal canal, the distal portion of the rectum, contains anal columns and a transition from columnar to stratified squamous epithelium.
    • The anal canal contains a network of veins that can distend and produce hemorrhoids under increased pressure.

    Sphincters

    • A smooth muscle internal anal sphincter controls the flow of feces, and is not under voluntary control.
    • The external anal sphincter is made of skeletal muscle and is under voluntary control.

    Anus

    • The anus, the exit of the anal canal, has keratinized epidermis.

    Absorption in the Large Intestine

    • The large intestine absorbs water and electrolytes, further concentrating fecal material.
    • The large intestine is responsible for the absorption of vitamins produced by bacterial action.

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