Digestive system

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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?

Contains nerve and blood vessels Signup and view all the answers

What mineral is essential for the formation of enamel?

Calcium Signup and view all the answers

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

Ankyloglossia Signup and view all the answers

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

Lingual frenulum Signup and view all the answers

Which structure helps to manipulate materials inside the mouth?

Tongue Signup and view all the answers

What is the function of the gingival sulcus?

It blocks bacteria from accessing deeper tissues. Signup and view all the answers

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

Periodontal ligament Signup and view all the answers

What distinguishes incisors from canines?

Canines have a sharp ridgeline and pointed tip. Signup and view all the answers

How many roots do premolars typically possess?

One or two Signup and view all the answers

Where is the apical foramen located?

At the opening of the root canal Signup and view all the answers

What does the root of a tooth sit in?

Alveolar bone Signup and view all the answers

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

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

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

Premolars Signup and view all the answers

What is the primary function of molars?

Crushing and grinding food Signup and view all the answers

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

20 Signup and view all the answers

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

Wisdom teeth Signup and view all the answers

Which of the following statements about permanent teeth is correct?

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

What common dental issue is associated with wisdom teeth?

Impacted teeth Signup and view all the answers

What distinguishes deciduous teeth from permanent teeth?

Deciduous teeth are also known as primary teeth. Signup and view all the answers

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

32 Signup and view all the answers

Which of the following is not a characteristic of molars?

Single root structure Signup and view all the answers

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

2 years Signup and view all the answers

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

32 Signup and view all the answers

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

They erode Signup and view all the answers

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

Wisdom teeth Signup and view all the answers

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

Crushing and grinding food Signup and view all the answers

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

Three roots Signup and view all the answers

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

Three Signup and view all the answers

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

Impacted tooth Signup and view all the answers

What is the primary function of the myenteric plexus?

To facilitate motor control of digestive muscle layers Signup and view all the answers

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

Muscularis externa Signup and view all the answers

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

Organization of actin and myosin filaments Signup and view all the answers

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

To regulate the movement along passageways Signup and view all the answers

Which structural feature is characteristic of smooth muscle?

Formation of a loose network of sarcoplasmic reticulum Signup and view all the answers

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

5–10 µm Signup and view all the answers

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

Submucosal plexus Signup and view all the answers

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

The inner layer is circular and the outer layer is longitudinal Signup and view all the answers

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

Peristalsis Signup and view all the answers

What role do enteroendocrine cells play in digestive activities?

They secrete hormones that regulate digestive functions. Signup and view all the answers

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

Small intestine Signup and view all the answers

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

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

Which structure plays a key role in the swallowing process?

Pharynx Signup and view all the answers

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

They provide support and anchorage for digestive organs. Signup and view all the answers

What is the primary role of the large intestine?

Formation and elimination of feces Signup and view all the answers

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

Gastrin Signup and view all the answers

What is the primary function of the gingival sulcus?

To prevent bacteria from accessing deeper tissues Signup and view all the answers

Which characteristic distinguishes canines from incisors?

Conical shape with a sharp ridgeline Signup and view all the answers

What is the role of the cement in a tooth?

To cover the dentin in the root Signup and view all the answers

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

Root Signup and view all the answers

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

Premolars Signup and view all the answers

What structure creates the gomphosis articulation?

Periodontal ligament Signup and view all the answers

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

Passageway for nerves and blood vessels Signup and view all the answers

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

Incisors Signup and view all the answers

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

Scattered throughout the sarcoplasm Signup and view all the answers

How do visceral smooth muscle cells contract?

In a wave as a single unit Signup and view all the answers

Where are multi-unit smooth muscle cells primarily located?

Walls of large arteries Signup and view all the answers

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

Visceral smooth muscle Signup and view all the answers

What stimulates visceral smooth muscle cells?

Neural, hormonal, or chemical stimulation Signup and view all the answers

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

It twists like a corkscrew Signup and view all the answers

Which location is associated with multi-unit smooth muscle?

Iris of the eye Signup and view all the answers

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

They resemble Z lines in skeletal muscle Signup and view all the answers

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

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

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

Mucosa Signup and view all the answers

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

Dense irregular connective tissue Signup and view all the answers

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

To perform mechanical processing and movement Signup and view all the answers

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

Serosa Signup and view all the answers

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

Smooth muscle Signup and view all the answers

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

To stabilize organs and prevent motion Signup and view all the answers

Which feature is characteristic of the large intestine wall?

Domination by mucin-secreting goblet cells Signup and view all the answers

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

Houses blood vessels and lymphatic vessels Signup and view all the answers

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

Lubricates feces as it becomes drier Signup and view all the answers

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

Smooth muscle Signup and view all the answers

Which of the following describes the external anal sphincter?

Under voluntary control Signup and view all the answers

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

Hemorrhoids Signup and view all the answers

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

Initiating physical changes in the digestive tract Signup and view all the answers

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

Myenteric reflexes Signup and view all the answers

What distinguishes long reflexes in the digestive system?

They involve the central nervous system. Signup and view all the answers

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

Cortisol Signup and view all the answers

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

Paralysis of smooth muscle leading to constipation Signup and view all the answers

Which statement best describes the function of enteroendocrine cells?

They produce hormones that regulate digestive processes. Signup and view all the answers

What triggers the myenteric reflexes in the digestive tract?

Activation of stretch or chemoreceptors Signup and view all the answers

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

Coordinated contraction of smooth muscle layers Signup and view all the answers

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

Congenital megacolon Signup and view all the answers

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

Pepsinogen Signup and view all the answers

How do parietal cells produce HCl without harming themselves?

By transporting H+ and Cl– ions separately 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?

Alkaline tide Signup and view all the answers

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

Rennin Signup and view all the answers

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

Bicarbonate secretion Signup and view all the answers

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

Carbonic anhydrase activity 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?

Hydrogen Signup and view all the answers

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

Bicarbonate is secreted inside the gastric glands. Signup and view all the answers

What is the primary role of pepsin in the stomach?

Digestion of proteins Signup and view all the answers

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

Parietal cells Signup and view all the answers

What is the role of the duodenum in digestive regulation?

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

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

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

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

It raises the level of CCK. Signup and view all the answers

What initiates the cephalic phase of gastric secretion?

The sight, smell, or thought of food. Signup and view all the answers

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

Food arriving in the stomach. Signup and view all the answers

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

Cholecystokinin Signup and view all the answers

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

After consuming a meal high in protein. Signup and view all the answers

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

It slows down digestion. 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?

Cephalic phase Signup and view all the answers

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

To coordinate digestive activities and enzyme secretion. Signup and view all the answers

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

Plasticity Signup and view all the answers

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

Peristalsis Signup and view all the answers

Which characteristic differentiates smooth muscle contraction from skeletal muscle contraction?

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

In which part of the digestive process does segmentation occur?

Small intestine and some large intestine areas Signup and view all the answers

What is NOT a characteristic of smooth muscle tone?

Constant tension regardless of conditions Signup and view all the answers

How do circular and longitudinal muscles function during peristalsis?

Circular muscles contract behind the bolus, longitudinal ahead Signup and view all the answers

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

To churn and fragment bolus contents Signup and view all the answers

What structural feature is characteristic of smooth muscle fibers?

Scattered arrangement of thick and thin filaments Signup and view all the answers

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

It features distinct intestinal glands with goblet cells. Signup and view all the answers

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

Longitudinal folds referred to as anal columns. Signup and view all the answers

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

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

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

Hemorrhoids Signup and view all the answers

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

To lubricate feces as they become drier. Signup and view all the answers

What shape does the sigmoid colon resemble?

S-shaped Signup and view all the answers

Where does the ascending colon begin?

At the cecum Signup and view all the answers

What structure supports the transverse colon?

Transverse mesocolon Signup and view all the answers

Which colon segment ends at the sigmoid flexure?

Descending colon Signup and view all the answers

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

It empties into the rectum. Signup and view all the answers

At which anatomical location does the ascending colon bend sharply?

Right colic flexure Signup and view all the answers

What is the approximate length of the sigmoid colon?

15 cm Signup and view all the answers

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

Transverse colon Signup and view all the answers

Which colon section is retroperitoneal?

Descending colon Signup and view all the answers

What is the primary function of the sigmoid colon?

Store waste Signup and view all the answers

What initiates the esophageal phase of swallowing?

The entrance of the bolus into the esophagus Signup and view all the answers

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

9 seconds Signup and view all the answers

What happens when a dry bolus is present during swallowing?

It requires secondary peristaltic waves Signup and view all the answers

What triggers the opening of the lower esophageal sphincter?

The approach of the bolus Signup and view all the answers

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

Stomach and most of the intestine Signup and view all the answers

What structure covers the organs enclosed by the peritoneal cavity?

Visceral peritoneum Signup and view all the answers

How much peritoneal fluid is typically secreted and reabsorbed daily?

7 liters Signup and view all the answers

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

Liver disease, kidney disease, and heart failure Signup and view all the answers

What condition can arise from the accumulation of peritoneal fluid?

Ascites Signup and view all the answers

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

Serous membrane Signup and view all the answers

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

V-shaped line of vallate papillae Signup and view all the answers

Which structure attaches the gums to the upper lip?

Frenulum of the upper lip Signup and view all the answers

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

Geniohyoid and mylohyoid muscles Signup and view all the answers

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

Oral vestibule Signup and view all the answers

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

Palatoglossal arch Signup and view all the answers

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

To facilitate food compression Signup and view all the answers

What is the role of gingivae in the oral cavity?

To provide a base for teeth Signup and view all the answers

What structure is located on either side of the uvula?

Palatopharyngeal arch Signup and view all the answers

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

Body of the tongue Signup and view all the answers

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

To attach the gums to the lower lip Signup and view all the answers

What is the primary function of the sigmoid colon?

Stores fecal matter Signup and view all the answers

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

Ascending colon Signup and view all the answers

What does the transverse colon primarily connect?

Ascending colon and descending colon Signup and view all the answers

How long is the sigmoid colon approximately?

15 cm Signup and view all the answers

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

Ascending colon Signup and view all the answers

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

Propulsion of materials through the digestive tract Signup and view all the answers

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

It is composed of four main layers Signup and view all the answers

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

Production of bile and digestive enzymes Signup and view all the answers

How do materials primarily move through the digestive tract?

Through rhythmic contractions of muscle layers Signup and view all the answers

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

Spleen Signup and view all the answers

What role do enteroendocrine cells play in the digestive system?

They regulate digestive hormone secretion Signup and view all the answers

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

Contains layers of muscle and connective tissue Signup and view all the answers

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

Spindle-shaped cells Signup and view all the answers

What are considered local factors in digestive activities?

Presence of chemicals in the digestive tract Signup and view all the answers

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

Triggered by stretch or chemoreceptors in the digestive tract Signup and view all the answers

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

Involve interneurons and CNS motor neurons Signup and view all the answers

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

18 Signup and view all the answers

What characterizes congenital megacolon (Hirschsprung disease)?

Absence or reduction of ganglion cells in the myenteric plexus Signup and view all the answers

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

External environmental factors Signup and view all the answers

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

Congenital megacolon Signup and view all the answers

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

Mechanical stretching of the digestive tract wall Signup and view all the answers

What role do enteroendocrine cells serve in the digestive system?

Producing digestive hormones Signup and view all the answers

What is the primary function of the large intestine?

Reabsorbing water and compacting intestinal contents into feces Signup and view all the answers

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

Cecum Signup and view all the answers

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

Ileum Signup and view all the answers

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

Functions as a lymphoid organ Signup and view all the answers

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

Thinner wall and larger diameter Signup and view all the answers

What triggers the gastric phase of secretion?

Presence of undigested materials in the stomach Signup and view all the answers

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

Generating important vitamins Signup and view all the answers

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

Increases mixing waves of stomach contractions Signup and view all the answers

What initiates the intestinal phase of gastric secretion?

Chyme entering the duodenum Signup and view all the answers

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

Cecum Signup and view all the answers

What is the average length of the large intestine?

1.5 m Signup and view all the answers

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

Inhibition of gastrin production Signup and view all the answers

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

Storing fecal material prior to defecation Signup and view all the answers

What occurs as a result of distention of the duodenum?

Initiation of the enterogastric reflex Signup and view all the answers

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

Secreting digestive enzymes Signup and view all the answers

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

It decreases gastric motility Signup and view all the answers

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

Gastroenteric reflex Signup and view all the answers

What increases in the duodenum during the intestinal phase?

Mucus production Signup and view all the answers

How long does the gastric phase typically last?

2–4 hours Signup and view all the answers

What role does gastrin play in stomach function?

Stimulates secretion from parietal and chief cells Signup and view all the answers

What function does the rectum serve in the digestive system?

Temporarily stores fecal material Signup and view all the answers

What are haustra in the large intestine responsible for?

Creating pouches in the colon wall Signup and view all the answers

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

Tenia coli Signup and view all the answers

What triggers mass movements in the large intestine?

Expansion of the stomach and duodenum Signup and view all the answers

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

Provide structural support to the colon Signup and view all the answers

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

To coordinate movements of smooth muscle Signup and view all the answers

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

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

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

Lack of sarcomeres and striations Signup and view all the answers

Where is the myenteric plexus located within the digestive tract?

Between the circular and longitudinal muscle layers Signup and view all the answers

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

30–200 µm Signup and view all the answers

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

Submucosal plexus Signup and view all the answers

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

Formation of well-defined striations Signup and view all the answers

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

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

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

Transport of materials to the stomach Signup and view all the answers

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

Secretion Signup and view all the answers

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

Small intestine Signup and view all the answers

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

Dehydration and compaction of indigestible materials Signup and view all the answers

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

Absorption Signup and view all the answers

Which statement accurately describes mechanical digestion?

It includes crushing and shredding food in the mouth. Signup and view all the answers

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

Ingestion Signup and view all the answers

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

Stomach Signup and view all the answers

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

To propel food into the esophagus Signup and view all the answers

Which of the following best describes chemical digestion?

Hydrolysis of molecules into absorbable units Signup and view all the answers

What primarily increases the absorptive capacity of the intestinal tract?

Circular folds Signup and view all the answers

What role do Paneth cells play in the intestinal glands?

Protection against pathogens Signup and view all the answers

What allows chylomicrons to be transported from the intestinal tract?

Lymphatic capillaries Signup and view all the answers

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

Jejunum Signup and view all the answers

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

Stem cells Signup and view all the answers

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

Capillary network Signup and view all the answers

What characterizes the epithelial surface of intestinal villi?

Microvilli Signup and view all the answers

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

Absorption of nutrients Signup and view all the answers

What type of projections do intestinal villi exhibit?

Fingerlike projections Signup and view all the answers

What do lymphatic capillaries transport that blood capillaries cannot?

Large protein-lipid packages Signup and view all the answers

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

Connects the root dentin to the alveolar bone Signup and view all the answers

Which feature distinguishes the cement from dentin in teeth?

Cement is less resistant to erosion than dentin Signup and view all the answers

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

Neck Signup and view all the answers

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

Canines Signup and view all the answers

Where are blood vessels and nerves located within a tooth?

Pulp cavity Signup and view all the answers

What is the primary function of the gingival sulcus?

To prevent bacterial access to the root Signup and view all the answers

What distinguishes premolars from other types of teeth?

They typically have one or two roots and flat crowns Signup and view all the answers

What is a defining characteristic of incisors?

They have a single root and a blade-like shape Signup and view all the answers

What role does the apical foramen serve in a tooth?

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

What differentiates the root from the crown of a tooth?

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

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

Increasing secretion by parietal and chief cells Signup and view all the answers

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

Activation of the enterogastric reflex Signup and view all the answers

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

Gastrin secretion Signup and view all the answers

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

Increases gastric motility Signup and view all the answers

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

Decreased chyme release into the duodenum Signup and view all the answers

What is the function of the esophagus?

To actively transport food and liquids to the stomach Signup and view all the answers

Which statement accurately describes the structural dimensions of the esophagus?

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

Which of the following statements about the pharynx is true?

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

What role does the upper esophageal sphincter serve?

It prevents air from entering the esophagus Signup and view all the answers

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

Oropharynx Signup and view all the answers

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

They maintain resting muscle tone in the circular muscle layer Signup and view all the answers

Where does the esophagus enter the abdominopelvic cavity?

Through the diaphragmatic hiatus Signup and view all the answers

What is the primary function of the lower esophageal sphincter?

Prevents backflow of stomach contents Signup and view all the answers

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

To move villi back and forth Signup and view all the answers

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

It increases surface area for absorption Signup and view all the answers

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

About 90% occurs in the small intestine Signup and view all the answers

What are the three segments of the small intestine?

Duodenum, jejunum, ileum Signup and view all the answers

What is the average length of the small intestine?

6 m (19.7 ft) Signup and view all the answers

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

Lacteal Signup and view all the answers

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

To transport fat-soluble nutrients Signup and view all the answers

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

4 cm (1.6 in.) Signup and view all the answers

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

Microvilli Signup and view all the answers

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

Epithelial cells in the villi Signup and view all the answers

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

Neutralization of acidic chyme Signup and view all the answers

Which characteristic is NOT true of the jejunum?

Located in the retroperitoneal space Signup and view all the answers

Which segment of the small intestine has the longest length?

Ileum Signup and view all the answers

What type of secretions are produced by duodenal glands?

Mucous secretions Signup and view all the answers

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

Presence of aggregated lymphoid nodules Signup and view all the answers

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

Jejunum Signup and view all the answers

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

In the retroperitoneal space Signup and view all the answers

What is a significant anatomical feature of the ileum?

Presence of Peyer's patches Signup and view all the answers

What impacts the function of the ileocecal valve?

Controls flow from the ileum to the cecum Signup and view all the answers

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

Relatively small and few Signup and view all the answers

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

To increase surface area for absorption of nutrients Signup and view all the answers

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

They release substances that contribute to innate immunity Signup and view all the answers

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

To carry absorbed nutrients to the hepatic portal circulation Signup and view all the answers

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

Circular folds (plicae circulares) 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?

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

Which characteristic distinguishes microvilli from intestinal villi?

Microvilli enhance the absorbent area more than villi Signup and view all the answers

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

Stem cells dividing and producing new epithelial cells Signup and view all the answers

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

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

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

Epithelial tissue Signup and view all the answers

What is the primary function of the esophagus?

To actively move food and liquids to the stomach Signup and view all the answers

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

Oropharynx Signup and view all the answers

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

Parasympathetic and sympathetic fibers Signup and view all the answers

At which location does the esophagus enter the abdominopelvic cavity?

Esophageal hiatus Signup and view all the answers

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

Skeletal muscle Signup and view all the answers

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

Prevents backflow of stomach contents Signup and view all the answers

How long is the esophagus in adults on average?

25 cm Signup and view all the answers

What is the narrowest point of the esophagus located near?

The cricoid cartilage Signup and view all the answers

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

Production of alkaline mucus Signup and view all the answers

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

Parietal cells Signup and view all the answers

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

3–7 days Signup and view all the answers

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

Muscular layer Signup and view all the answers

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

Mucus and hormones Signup and view all the answers

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

Submucosa Signup and view all the answers

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

Buccal phase Signup and view all the answers

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

Skeletal muscle Signup and view all the answers

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

Entry into the oropharynx Signup and view all the answers

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

Soft palate Signup and view all the answers

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

Anchoring the esophagus Signup and view all the answers

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

It transitions from skeletal to mixed to smooth muscle Signup and view all the answers

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

Pharyngeal muscle contraction Signup and view all the answers

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

It is folded down Signup and view all the answers

Which phase of swallowing is strictly voluntary?

Buccal phase Signup and view all the answers

Which of the following accurately describes the digestive system?

It includes the digestive tract and accessory organs. Signup and view all the answers

What is the primary function of the digestive system?

To supply nutrients for cell maintenance and growth. Signup and view all the answers

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

Cardiovascular and urinary systems. Signup and view all the answers

What distinguishes the digestive tract's structure?

It has regions with permanent ridges and temporary folds. Signup and view all the answers

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

They produce enzymes secreted into the digestive tract. Signup and view all the answers

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

It removes waste products generated by cell activity. Signup and view all the answers

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

They increase the surface area for nutrient absorption. Signup and view all the answers

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

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

Which statement best describes the accessory organs of digestion?

They secrete products required for the digestion process. Signup and view all the answers

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

To ensure proper nutrition and waste management. Signup and view all the answers

What initiates the esophageal phase of swallowing?

The bolus being forced through the entrance to the esophagus Signup and view all the answers

How does a dry bolus affect the swallowing process?

It may necessitate secondary peristaltic waves Signup and view all the answers

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

9 seconds Signup and view all the answers

What triggers the opening of the lower esophageal sphincter?

The approach of the bolus Signup and view all the answers

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

Visceral peritoneum Signup and view all the answers

What is the main function of the peritoneal fluid?

To facilitate movement between the parietal and visceral layers Signup and view all the answers

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

50 mL Signup and view all the answers

What condition may result from an accumulation of peritoneal fluid?

Ascites Signup and view all the answers

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

Liver disease Signup and view all the answers

Which layer lines the inner surface of the peritoneal cavity?

Parietal peritoneum Signup and view all the answers

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

Skeletal muscle Signup and view all the answers

What occurs during the buccal phase of swallowing?

The bolus is compressed against the hard palate. Signup and view all the answers

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

Mucosa and submucosa Signup and view all the answers

Which phase of swallowing is considered strictly voluntary?

Buccal phase Signup and view all the answers

What is the function of the adventitia in the esophagus?

Anchors the esophagus to the posterior body wall Signup and view all the answers

During which phase of swallowing is the larynx elevated?

Pharyngeal phase Signup and view all the answers

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

Smooth muscle only Signup and view all the answers

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

It involves tactile receptors triggering motor commands. Signup and view all the answers

What age do children typically have 20 deciduous teeth?

2 years Signup and view all the answers

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

32 Signup and view all the answers

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

Wisdom teeth Signup and view all the answers

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

They are pushed aside or fall out Signup and view all the answers

What conditions could lead to a tooth becoming impacted?

Overcrowding from adjacent teeth Signup and view all the answers

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

3 Signup and view all the answers

What is the main function of molars?

Crushing and grinding Signup and view all the answers

What common dental issue is especially associated with wisdom teeth?

Impaction Signup and view all the answers

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

Reabsorbing water Signup and view all the answers

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

Cecum Signup and view all the answers

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

Primary teeth Signup and view all the answers

What number of roots do upper jaw molars typically have?

3 Signup and view all the answers

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

Appendix 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?

Larger diameter and thinner walls Signup and view all the answers

What is the average length of the large intestine?

1.5 m Signup and view all the answers

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

To manipulate materials inside the mouth Signup and view all the answers

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

Calcium phosphate Signup and view all the answers

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

Ankyloglossia Signup and view all the answers

What does the fauces connect?

Oral cavity and oropharynx Signup and view all the answers

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

Vitamins Signup and view all the answers

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

Dentin Signup and view all the answers

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

Crushing and slicing food Signup and view all the answers

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

To regulate the passage of chyme into the small intestine Signup and view all the answers

What is required for the formation of enamel?

Calcium Signup and view all the answers

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

Lesser omentum Signup and view all the answers

What is located in the interior chamber of the tooth?

Pulp cavity Signup and view all the answers

What can result from ankyloglossia in newborns?

Interference with breastfeeding Signup and view all the answers

What is chyme primarily composed of?

Food, saliva, and gastric gland secretions Signup and view all the answers

Which stomach region functions mainly as a mixing bowl?

Body Signup and view all the answers

How much material can the stomach typically hold when full?

1.5 liters Signup and view all the answers

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

To secrete mucus for protection Signup and view all the answers

What shape does the stomach take when it is empty?

Muscular tube with constricted lumen Signup and view all the answers

Which curvature of the stomach forms the medial surface?

Lesser curvature Signup and view all the answers

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

1,500 ml Signup and view all the answers

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

Fundus Signup and view all the answers

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

Stratified squamous epithelium Signup and view all the answers

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

Villi Signup and view all the answers

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

Lamina propria Signup and view all the answers

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

Inner circular layer and outer longitudinal layer Signup and view all the answers

Which type of stimulation decreases digestive muscle tone and activity?

Sympathetic stimulation Signup and view all the answers

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

Plicae circulares Signup and view all the answers

What is the primary function of the submucosal neural plexus?

To innervate the mucosa and submucosa Signup and view all the answers

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

Submucosal neural plexus Signup and view all the answers

What role does the duodenum play in the digestive process?

It regulates gastric activity and digestive secretion. Signup and view all the answers

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

Cephalic phase Signup and view all the answers

What is the function of secretin in the digestive process?

It helps regulate the water content in chyme. Signup and view all the answers

What triggers the gastric phase of secretion?

Distention of the stomach Signup and view all the answers

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

It raises levels. Signup and view all the answers

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

To manipulate materials inside the mouth Signup and view all the answers

What does the frenulum of the tongue do?

Connects the tongue to the floor of the mouth Signup and view all the answers

What is an effect of ankyloglossia?

Challenges with breastfeeding Signup and view all the answers

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

Enamel Signup and view all the answers

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

Water, mucins, and lingual lipase Signup and view all the answers

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

Vascular and nerve components Signup and view all the answers

Which statement about enamel is correct?

It's the hardest biologically manufactured substance Signup and view all the answers

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

To facilitate slicing and chewing food Signup and view all the answers

What materials are necessary for the formation of enamel?

Calcium, phosphate, and vitamin D Signup and view all the answers

What is the composition of dentin?

A mineralized matrix similar to bone Signup and view all the answers

What is the main purpose of the gingival sulcus?

To block bacteria from accessing deeper tissues. Signup and view all the answers

Which tooth region is located below the gum line?

Root Signup and view all the answers

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

Incisors Signup and view all the answers

What is the characteristic feature of canines?

Conical shape with a sharp ridgeline Signup and view all the answers

How many roots can premolars have?

One Signup and view all the answers

Which structure creates the gomphosis articulation in a tooth?

Periodontal ligament Signup and view all the answers

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

To house blood vessels and nerves. Signup and view all the answers

Which of the following statements about cement is true?

It covers the dentin in the root. Signup and view all the answers

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

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

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

Molars Signup and view all the answers

What is the primary function of the digestive system?

To break down food and absorb nutrients Signup and view all the answers

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

Liver Signup and view all the answers

Which layer of the digestive tract is responsible for peristalsis?

Circular muscle layer Signup and view all the answers

Which process primarily occurs in the small intestine?

Nutrient absorption Signup and view all the answers

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

Smooth muscle Signup and view all the answers

What role do enteroendocrine cells play in digestion?

Regulate digestive hormones Signup and view all the answers

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

Single nucleus per cell Signup and view all the answers

Which structure is primarily involved in the swallowing process?

Pharynx Signup and view all the answers

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

Mixing and churning food Signup and view all the answers

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

Large intestine Signup and view all the answers

What are the major functions of the large intestine?

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

What are the four regions of the colon?

Ascending colon, transverse colon, descending colon, sigmoid colon. Signup and view all the answers

What are mass movements in the large intestine?

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

The wall of the large intestine contains villi.

False Signup and view all the answers

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

Mucin-secreting goblet cells. Signup and view all the answers

What is the primary function of the internal anal sphincter?

To control the involuntary release of feces. Signup and view all the answers

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

Skeletal muscle. Signup and view all the answers

What happens to the epithelium at the anus?

It becomes keratinized. Signup and view all the answers

Increased venous pressure in the rectum can lead to hemorrhoids.

True Signup and view all the answers

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

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

The digestive tract begins at the and ends at the .

mouth, anus Signup and view all the answers

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

submucosa, serosa Signup and view all the answers

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

Epithelia Signup and view all the answers

What is peristalsis?

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

Smooth muscle cells contain striations.

False Signup and view all the answers

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

Visceral smooth muscle Signup and view all the answers

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

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

What are the primary stimuli for digestive activities?

Changes in pH of contents Signup and view all the answers

What are the hormonal control mechanisms involved in digestive function?

At least 18 hormones produced by enteroendocrine cells. Signup and view all the answers

What characterizes congenital megacolon (Hirschsprung disease)?

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

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

Peristalsis Signup and view all the answers

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

Hormonal and neural mechanisms. Signup and view all the answers

Describe enteroendocrine cells.

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

What is ingestion?

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

What is the primary function of the esophagus?

Transport of materials to the stomach. Signup and view all the answers

What is the role of the stomach in digestion?

Chemical breakdown and mechanical processing. Signup and view all the answers

What type of epithelium lines the oral cavity?

Stratified squamous Signup and view all the answers

What are the four types of teeth?

Incisors, canines, premolars, and molars. Signup and view all the answers

What is an impacted tooth?

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

What is the function of the esophagus?

Actively moves food and liquids to the stomach Signup and view all the answers

What is the approximate length of the esophagus?

25 cm (10 in.) Signup and view all the answers

What structures does the esophagus descend posterior to?

The trachea Signup and view all the answers

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

All of the above Signup and view all the answers

What are the three phases of swallowing?

Buccal phase, Pharyngeal phase, Esophageal phase Signup and view all the answers

What is the role of the upper esophageal sphincter?

Prevents air from entering the esophagus Signup and view all the answers

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

9 seconds Signup and view all the answers

What is the function of the pyloric sphincter?

Regulates release of chyme into the duodenum Signup and view all the answers

Which cells secrete hydrochloric acid in the stomach?

Parietal cells Signup and view all the answers

What is the function of intrinsic factor?

Aids in vitamin B12 absorption Signup and view all the answers

What are circular folds in the small intestine?

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

What are intestinal villi?

Fingerlike projections of mucosa covered by epithelial cells. Signup and view all the answers

What role do Paneth cells play in the intestines?

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

What is the average length of the small intestine?

6 m (19.7 ft) Signup and view all the answers

Which segments make up the small intestine?

Jejunum Signup and view all the answers

What is the primary function of the duodenum?

To neutralize acidic chyme. Signup and view all the answers

What is the total length of the large intestine?

~1.5 m (4.9 ft) Signup and view all the answers

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

Rectum Signup and view all the answers

What is the main function of the colon?

To reabsorb water and compact intestinal contents into feces. Signup and view all the answers

What are the parts of the colon?

Transverse colon Signup and view all the answers

What triggers the urge to defecate?

Movement of fecal material into the rectum. Signup and view all the answers

Which of the following organs is considered to have a subperitoneal position?

Kidney Signup and view all the answers

What is the primary purpose of mesentery in the peritoneal cavity?

To facilitate neurovascular communication Signup and view all the answers

Which specific term refers to the double layer of peritoneum associated with the colon?

Mesocolon Signup and view all the answers

What distinguishes intraperitoneal organs from extraperitoneal organs?

Intraperitoneal organs are fully covered by peritoneum Signup and view all the answers

Which statement best explains the function of the fibrous response in mesh repair for hernias?

The body’s reaction strengthens the area Signup and view all the answers

Which of the following is NOT a specific type of mesentery?

Mesopulmonis Signup and view all the answers

What is typically meant by the term 'mesentery' in anatomical discussions?

Generally refers to the mesentery of the small intestine Signup and view all the answers

Which of the following best describes the continuity provided by mesentery?

Connects visceral and parietal peritoneum Signup and view all the answers

What is the main function of the greater omentum in the abdominal cavity?

To store fat and cushion the abdominal organs Signup and view all the answers

Which of the following statements about the lesser omentum is correct?

It connects the liver to the greater curvature of the stomach Signup and view all the answers

What characteristic describes the infracolic compartment?

It is divided into left and right infracolic spaces Signup and view all the answers

What role do paracolic gutters play in the abdominal cavity?

They separate the supracolic and infracolic compartments Signup and view all the answers

The omental bursa is located posterior to which structures?

The stomach and lesser omentum Signup and view all the answers

What is the primary feature of the mesentery in the abdominal cavity?

It supports the intestines and contains blood vessels Signup and view all the answers

Which structure forms the major part of the abdominopelvic cavity?

Peritoneum Signup and view all the answers

What is a key characteristic of the greater pelvis?

It supports lower abdominal viscera. Signup and view all the answers

Which of the following is NOT a function associated with the omental bursa?

Functioning as a storage site for digestive enzymes Signup and view all the answers

How does the mesentery contribute to the organization of the abdominal cavity?

By connecting various organs and providing a pathway for vessels Signup and view all the answers

Which anatomy is primarily concerned with the musculature of the posterior abdominal wall?

Blood supply Signup and view all the answers

Which of the following compartments is part of the peritoneal cavity?

Infracolic compartment Signup and view all the answers

Which type of organs are primarily categorized as intraperitoneal?

Spleen Signup and view all the answers

What anatomical feature provides free movement of the stomach on adjacent structures?

The lesser omentum Signup and view all the answers

What does the peritoneal cavity primarily extend between?

The thoracic diaphragm and pelvic diaphragm Signup and view all the answers

Which structure is continuous with the pelvic cavity?

Peritoneum Signup and view all the answers

Which of the following correctly describes the location of retroperitoneal organs?

They lie behind the peritoneum. Signup and view all the answers

Which of the following best classifies the function of the mesentery?

It anchors the abdominal organs and contains blood vessels. Signup and view all the answers

What is the primary role of the peritoneum in abdominal organ protection?

It provides lubrication and reduces friction. Signup and view all the answers

Which of the following identifies one of the subdivisions of the peritoneal cavity?

Abdominal cavity Signup and view all the answers

What comprises the posterior layer of the rectus sheath above the arcuate line?

Aponeuroses of the posterior lamina of the internal oblique and transversus abdominis Signup and view all the answers

Which statement accurately describes the contents left posterior to the rectus abdominis below the arcuate line?

It includes extraperitoneal fat and peritoneum. Signup and view all the answers

What are the functions of the superficial epigastric vessels mentioned in the context of the rectus sheath?

Supplying the superficial abdominal wall of the pubic and inferior umbilical regions. Signup and view all the answers

The linea alba is best described as which of the following?

A band of interlaced fibers separating bilateral rectus sheaths Signup and view all the answers

Which of the following accurately describes the umbilical ring?

A defect in the linea alba through which the fetal umbilical vessels passed. Signup and view all the answers

What does the transverse mesocolon divide the abdominal cavity into?

Supracolic and infracolic compartments Signup and view all the answers

Which of the following is NOT a characteristic of extraperitoneal organs?

They are completely surrounded by peritoneum Signup and view all the answers

What forms the superior boundary of the posterior abdominal wall?

Diaphragm Signup and view all the answers

Which muscle is NOT part of the posterior abdominal wall?

Transversus abdominis Signup and view all the answers

What is the primary role of the mesenteries in the abdominal cavity?

To hold the abdominal organs in place Signup and view all the answers

Which of the following is included in the supracolic compartment?

Stomach Signup and view all the answers

Which term best represents organs that are entirely surrounded by peritoneum?

Intraperitoneal Signup and view all the answers

The lumbar plexus consists primarily of which part of the nervous system?

Anterior rami of lumbar nerves Signup and view all the answers

Which of the following abdominal wall muscles is primarily responsible for flexing the hip?

Psoas major Signup and view all the answers

Which structure is found in the posterior abdominal wall and provides support for the spinal column?

Lumbar vertebrae Signup and view all the answers

Which of the following muscles is classified as an external abdominal muscle?

External oblique Signup and view all the answers

Which muscle primarily acts to compress the abdominal cavity?

Transversus abdominis Signup and view all the answers

What is the anatomical position of the rectus abdominis muscle?

Found vertically along the midline of the abdomen Signup and view all the answers

Which option correctly describes the internal oblique muscle?

It assists in rotation of the torso. Signup and view all the answers

Which abdominal muscle is primarily responsible for producing flexible trunk movements?

Rectus abdominis Signup and view all the answers

What structure is defined by the tendinous intersections of the rectus abdominis muscle?

Abs or packs Signup and view all the answers

Which plane divides the abdomen into left and right halves?

Vertical median plane Signup and view all the answers

At which vertebral level does the transverse umbilical plane typically occur?

L3 and L4 Signup and view all the answers

What is the approximate location of the transtubercular plane?

At the level of L5 vertebra Signup and view all the answers

What does the semilunar line parallel to the linea alba define?

Lateral wall of the rectus abdominis muscle Signup and view all the answers

The transpyloric plane is used interchangeably with which other plane?

Subcostal plane Signup and view all the answers

What major abdominal organ does the transpyloric plane transect?

Gallbladder Signup and view all the answers

What does the midline raphe extend from?

Xiphoid process to the pubic symphysis Signup and view all the answers

What is one of the primary components of the superficial fascia or subcutaneous tissue?

Fat storage Signup and view all the answers

Which layer of the fascia is reinforced with elastic and collagen fibers inferior to the umbilicus?

Deep membranous layer Signup and view all the answers

What forms the external aspects of the three flat muscles in the anterolateral abdominal wall?

Aponeuroses Signup and view all the answers

What is the significance of the Linea Alba in the abdominal wall?

It connects the abdominal muscles Signup and view all the answers

What type of fascia is known as the Transversalis Fascia?

Endoabdominal fascia Signup and view all the answers

Which layer is a single layer of epithelial cells and associated connective tissue in the abdominal wall?

Parietal peritoneum Signup and view all the answers

Where does the superficial perineal fascia (Colles fascia) continue inferiorly from?

Deep membranous layer Signup and view all the answers

What is the primary distinguishing feature of the investing fascia in the abdominal wall?

It covers muscle structures Signup and view all the answers

What type of fat separates the Transversalis fascia from the Parietal peritoneum?

Extraperitoneal fat Signup and view all the answers

What are the three flat muscles located laterally in the abdominal wall?

External Oblique, Internal Oblique, Transversus Abdominis Signup and view all the answers

What defines a mesentery in the abdominal cavity?

A double layer of peritoneum that provides neurovascular communication Signup and view all the answers

Which organ is typically associated with a specific type of mesentery?

Esophagus Signup and view all the answers

What is the primary purpose of using mesh in hernia repairs?

To enhance the fibrosis response from the body Signup and view all the answers

Which of the following organs is subperitoneal?

Kidney Signup and view all the answers

What does the term 'transversalis fascia' refer to in hernia management?

A layer of tissue used in the hernia repair process Signup and view all the answers

What are the transverse and sigmoid mesocolons associated with?

Colon Signup and view all the answers

Which of the following structures is NOT related to the mesentery concept?

Parietal peritoneum Signup and view all the answers

What is a key feature of subperitoneal organs?

They are anchored to the body but partially exposed. Signup and view all the answers

What type of hernia repair technique involves placing mesh on the posterior wall of the inguinal canal?

Lichtenstein repair Signup and view all the answers

Which nerve type does the mesentery typically provide communication for?

Neurovascular nerves Signup and view all the answers

What is a primary function of the abdominal muscles?

Support for the anterolateral abdominal wall Signup and view all the answers

How do abdominal muscles contribute to the protection of the abdominal viscera?

By compressing the contents to maintain intraabdominal pressure Signup and view all the answers

What is one role of abdominal muscles in movement?

Flexing and rotating the trunk Signup and view all the answers

What effect do abdominal muscles have when exposed to cold temperatures?

They contract to produce heat Signup and view all the answers

Which muscles work together to perform torsional movement of the trunk?

Contralateral Internal Oblique and external obliques Signup and view all the answers

What structure does the Dartos muscle associate with?

The scrotum Signup and view all the answers

What happens to the scrotal skin in response to cold temperature?

It wrinkles due to muscle contraction Signup and view all the answers

What is a function of abdominal muscles related to posture?

Maintaining trunk alignment and stability Signup and view all the answers

Which statement best describes the compression function of abdominal muscles?

They maintain or increase intraabdominal pressure Signup and view all the answers

What condition is characterized by undescended testes?

Cryptorchidism Signup and view all the answers

What type of hernia is usually caused by the opening of investing fascia during surgery?

Incisional hernia Signup and view all the answers

Which structure guides the pathway for the descent of the testis?

Gubernaculum Signup and view all the answers

In the determination of hernia types in children, which finger is typically used for the physical examination?

Pinky finger Signup and view all the answers

Which layer of the peritoneum covers the internal aspect of the abdominal cavity?

Parietal peritoneum Signup and view all the answers

What is the purpose of a midline incision that avoids the umbilical area?

To allow for better aesthetic healing. Signup and view all the answers

Which structure serves as the most inferior boundary of the abdomen?

Pelvic girdle Signup and view all the answers

What is one reason for using a midline incision in cases of stab wounds without removing the penetrating material?

To assess the extent of organ involvement. Signup and view all the answers

Which component is NOT part of the pelvic girdle?

Sacrum Signup and view all the answers

What is the relationship between the abdomen and pelvis?

There is no actual structural separation. Signup and view all the answers

Which anatomical feature is included in the upper boundary of the abdomen?

Costal margin Signup and view all the answers

Why is the umbilical area avoided during a midline incision?

To improve healing aesthetics and due to its depth. Signup and view all the answers

What does the term inguinal ligament refer to?

A connective tissue structure at the lower abdomen. Signup and view all the answers

What structure does the interweaving of the aponeuroses form?

Rectus sheath Signup and view all the answers

Which muscle works alongside the external oblique to perform torsional movements of the trunk?

Internal oblique Signup and view all the answers

How do the fibers of the external oblique run?

Inferomedially Signup and view all the answers

What action is the external oblique NOT involved in?

Extending the arm Signup and view all the answers

In which direction does the superficial layer of external oblique fibers run as they approach the iliac crest?

Almost parallel Signup and view all the answers

What type of movement is characterized by the external and internal oblique working together at the torso?

Torsional movement Signup and view all the answers

What is the function of both external and internal oblique muscles when pulling the body?

From cephalic to caudal portion Signup and view all the answers

What is the function of the interspinous plane in the anterior abdominal wall?

Delineates the middle and lower thirds horizontally Signup and view all the answers

What is the anatomical significance of the inguinal region?

It serves as a pathway for structures exiting and entering the abdominal cavity. Signup and view all the answers

What is a mnemonic to remember the relationship between the external and internal oblique?

Hands in your pockets Signup and view all the answers

Which plane passes through the palpated anterior superior iliac spine (ASIS) on each side?

Midinguinal plane Signup and view all the answers

Which of the following statements is true regarding the relationship of external and internal oblique fibers?

They interweave at specific angles Signup and view all the answers

What structure conveys sperms from the epididymis to the ejaculatory duct?

Ductus deferens (vas deferens) Signup and view all the answers

What does the subcostal plane separate in the abdominal wall?

Upper and middle thirds of the abdomen Signup and view all the answers

Which muscle is the outermost layer of abdominal muscles?

External oblique Signup and view all the answers

Which of the following correctly describes the alignment of the midclavicular planes?

They connect the ASIS to the pubic symphysis Signup and view all the answers

Where does the testicular artery arise from?

The aorta Signup and view all the answers

What anatomical feature does the transtubercular plane usually correspond to?

Body of L5 Signup and view all the answers

What is the role of the genital branch of the genitofemoral nerve?

To supply the cremaster muscle Signup and view all the answers

What is a potential clinical significance of the inguinal region?

It has pathways that are potential sites for herniation. Signup and view all the answers

Which of the following describes the relationship between the left and right midclavicular planes?

They delineate the left and right sides of the abdomen Signup and view all the answers

Which artery arises from the inferior vesical artery?

Artery of ductus deferens Signup and view all the answers

Where does the subcostal plane pass through in the abdominal cavity?

Inferior border of the 10th costal cartilage Signup and view all the answers

What is the primary purpose of the four planes that delineate the regions of the abdominal wall?

To divide the abdomen into functional regions Signup and view all the answers

What is a vestige of the processus vaginalis?

A fibrous thread in the spermatic cord Signup and view all the answers

What function does sympathetic nerve fibers have on the ductus deferens?

They control contractions of the ductus deferens. Signup and view all the answers

Which type of plane is the interspinous or transtubercular plane classified as?

Transverse plane Signup and view all the answers

How many sagittal planes are used to delineate the abdominal wall?

Two Signup and view all the answers

What is the anatomical landmark that defines the anterior limit of the inguinal region?

Anterior superior iliac spine (ASIS) Signup and view all the answers

Which of the following arteries supplies the cremaster muscle?

Cremasteric artery Signup and view all the answers

Which of the following structures is part of the anterior abdominal wall?

Peritoneum Signup and view all the answers

What is the primary function of the rectus sheath?

Protect the abdominal cavity Signup and view all the answers

What are the midinguinal points used to identify?

Midpoints between the anterior superior iliac spine (ASIS) and pubic tubercles Signup and view all the answers

Which of the following is NOT a type of muscle in the anterior abdominal wall?

Circular muscles Signup and view all the answers

What composes the boundaries of the anterior abdominal wall?

Upper and lower boundaries defined by muscle layers Signup and view all the answers

Which region is recognized for common pathologies related to the abdominal cavity?

Inguinal hernias Signup and view all the answers

What is the anatomical significance of the peritoneal cavity?

Serves as a lubricated space for abdominal organs Signup and view all the answers

Which of the following components does NOT belong to the posterior abdominal wall?

Abdominal muscles Signup and view all the answers

What is the main purpose of Hesselbach’s triangle in the context of inguinal hernias?

To differentiate between direct and indirect hernias Signup and view all the answers

Which structure forms the medial boundary of the subinguinal space?

Lacunar ligament Signup and view all the answers

What is the role of the iliopubic tract in relation to the inguinal region?

It is behind the inguinal ligament Signup and view all the answers

Which layer provides cover for the inguinal canal?

External oblique aponeurosis Signup and view all the answers

What anatomical feature is characterized as a dense band forming the inferiormost part of the external oblique aponeurosis?

Inguinal ligament Signup and view all the answers

Which structure forms the superior and major part of the abdominopelvic cavity?

Superior peritoneum Signup and view all the answers

What anatomical area does the diaphragm separate from the abdominopelvic cavity?

Thoracic cavity Signup and view all the answers

Which layer is located at the most superficial level of the abdomen?

Superficial fascia Signup and view all the answers

What is the primary blood supply to the posterior abdominal wall?

Lumbar arteries Signup and view all the answers

Which of the following is NOT a component of the posterior abdominal wall?

Diaphragm Signup and view all the answers

Which part of the abdomen is supported by the greater pelvis?

Lower abdominal viscera Signup and view all the answers

Which structure provides no floor due to its continuity with the pelvic cavity?

Abdominal cavity Signup and view all the answers

Which of the following is an anatomical landmark of the anterior abdominal wall?

Rectus sheath Signup and view all the answers

Which of the following best describes the peritoneal cavity?

A continuous cavity extending to the pelvic diaphragm Signup and view all the answers

What is primarily illustrated by the quadrants and regions of the abdomen?

Clinical applications Signup and view all the answers

What structure forms the lateral border of the Inguinal or Hesselbach’s triangle?

Inguinal ligament Signup and view all the answers

Which of the following is NOT a type of inguinal hernia?

Umbilical hernia Signup and view all the answers

Where is the iliac crest located?

At the level of the L4 vertebra Signup and view all the answers

What is the role of the superficial epigastric veins?

To carry blood toward the pubic region Signup and view all the answers

Which muscle may increase the number of visible abdominal muscles?

Pyramidalis Signup and view all the answers

What defines the extent and boundaries of the inguinal canal?

Superficial and deep inguinal rings Signup and view all the answers

What anatomical feature lies deep to the skin crease marking the lower abdominal wall?

Inguinal ligament Signup and view all the answers

Which of the following statements about the inguinal area is true?

It includes the fascias of the external oblique muscle. Signup and view all the answers

Which statement best differentiates indirect inguinal hernias?

They enter the inguinal canal through the deep ring. Signup and view all the answers

What is the primary function of the inguinal canal?

To allow passage for the spermatic cord or round ligament Signup and view all the answers

Which arteries supply the upper third of the abdominal cavity?

Musculophrenic and Superior Epigastric Arteries Signup and view all the answers

The venous drainage of the abdominal wall is generally parallel to which of the following?

Arterial supply Signup and view all the answers

Which veins are known to drain into the Axillary vein and Superficial Epigastric vein?

Thoraco-epigastric vein Signup and view all the answers

Which of the following arteries supplies the deeper portions of the inferior abdominal wall?

Inferior Epigastric and Deep Circumflex Iliac arteries Signup and view all the answers

Which artery anastomoses with the inferior epigastric artery in the umbilical region?

Superior Epigastric artery Signup and view all the answers

What anatomical feature surrounds the umbilicus as all layers of the abdominal wall fuse?

Subcutaneous tissue Signup and view all the answers

Which arteries are responsible for supplying the sides of the abdominal wall?

10th and 11th Posterior Intercostal Arteries and Subcostal Artery Signup and view all the answers

What happens to the umbilicus as fat accumulates in the postnatal stage?

It becomes depressed Signup and view all the answers

Which vein is specifically mentioned to be between the Superficial Epigastric and Lateral Thoracic veins?

Thoraco-epigastric vein Signup and view all the answers

What is the primary role of the arteries supplying the abdominal wall?

To supply blood to the abdominal cavity Signup and view all the answers

Which layer of subcutaneous tissue or superficial fascia is considered the 'deep membranous layer'?

Scarpa’s fascia Signup and view all the answers

Which muscles are responsible for the compression of the abdomen?

Transversus Abdominis Signup and view all the answers

Which nerves provide the nerve supply for abdominal muscles?

Anterior rami of T7-L1 Signup and view all the answers

Which structure is found at McBurney’s point?

Appendix Signup and view all the answers

Which of the following is NOT a content of the spermatic cord?

Epididymis Signup and view all the answers

What separates the abdominal wall into its middle and lower thirds?

Interspinous plane Signup and view all the answers

Which transverse plane passes through the inferior border of the 10th costal cartilage?

Subcostal plane Signup and view all the answers

What does the midinguinal plane connect to in the layout of the abdominal wall?

Superior edge of the pubic symphysis Signup and view all the answers

Which planes delineate the abdominal regions vertically?

Midclavicular and midinguinal planes Signup and view all the answers

Which anatomical reference is used to define the subcostal plane?

Inferior border of the 10th costal cartilage Signup and view all the answers

What is the main role of the transtubercular plane in the abdominal quadrants?

Defining the middle and lower thirds Signup and view all the answers

Which two sagittal planes are utilized to delineate the abdominal quadrants?

Midclavicular and midinguinal planes Signup and view all the answers

What anatomical landmarks do the midclavicular planes pass through?

Midpoints of the ASIS and pubic symphysis Signup and view all the answers

What is the orientation of the fibers of the internal oblique muscles?

They run superomedially. Signup and view all the answers

Where do the lowermost fibers of the internal oblique muscles arise?

From the lateral half of the inguinal ligament. Signup and view all the answers

What structure is formed by the aponeurotic fibers of the internal oblique muscles?

The Rectus Sheath. Signup and view all the answers

What role does the Cremaster muscle play in males?

It elevates the testes when exposed to cold. Signup and view all the answers

How does the fiber arrangement of the internal oblique muscles compare with that of the external oblique muscles?

They run perpendicular to external oblique fibers. Signup and view all the answers

What is the internal oblique muscle classified as?

Middle (intermediate) abdominal muscle. Signup and view all the answers

What happens to the internal oblique muscle fibers at the midclavicular line?

They become aponeurotic. Signup and view all the answers

Which of the following describes the function of the internal oblique muscles?

They aid in rotating the torso. Signup and view all the answers

Which abdominal muscle group does the internal oblique lie beneath?

External Oblique. Signup and view all the answers

What does the median umbilical ligament represent?

Connection between the umbilicus and the bladder Signup and view all the answers

Which structure covers the inferior epigastric vessels?

Lateral umbilical folds Signup and view all the answers

What condition is characterized by the presence of air in the peritoneal cavity?

Pneumoperitoneum Signup and view all the answers

What is a common symptom of pneumoperitoneum?

Drawing in of the abdomen as the chest expands Signup and view all the answers

Which pathology results from excess fluid in the peritoneal cavity?

Ascites Signup and view all the answers

Which of the following is a potential cause of ascites?

Mechanical injury Signup and view all the answers

What distinguishes pneumoperitoneum from a gastric bubble?

Pneumoperitoneum occurs due to perforation of viscera Signup and view all the answers

What is the counterpart of pneumoperitoneum in the thorax?

Pneumothorax Signup and view all the answers

What effect does ascites have on the movements of viscera?

Interferes with movements Signup and view all the answers

What does the medial umbilical folds lie lateral to?

Median umbilical ligament Signup and view all the answers

What condition typically occurs due to the persistence of the processus vaginalis?

Indirect inguinal hernia Signup and view all the answers

Which type of hernia is characterized by a direct weakness of the abdominal wall and is located in Hesselbach's triangle?

Direct inguinal hernia Signup and view all the answers

At what stage of gestation does the testis begin its descent towards the scrotum?

7 weeks Signup and view all the answers

What anatomical feature connects the ovaries and the primordial uterus to the labia majus in females?

Gubernaculum Signup and view all the answers

Which type of inguinal hernia involves both direct and indirect hernia characteristics?

Pantaloon hernia Signup and view all the answers

In a newborn, what happens to the stalk of the processus vaginalis?

It becomes obliterated Signup and view all the answers

What is a common condition associated with direct inguinal hernias in patients?

Chronic obstructive pulmonary disease (COPD) Signup and view all the answers

What area of the body is associated with an epigastric hernia?

Epigastric area Signup and view all the answers

Which conclusion can be drawn regarding testis movement during fetal development?

Testis travels with testicular vessels to the scrotum Signup and view all the answers

What is the structure left behind after the obliteration of the processus vaginalis in newborns?

Tunica vaginalis 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