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What is the primary function of the digestive system?
What is the primary function of the digestive system?
The liver is directly a part of the digestive tract.
The liver is directly a part of the digestive tract.
False
Name the outermost layer of the digestive tract wall.
Name the outermost layer of the digestive tract wall.
Serosa or adventitia
The process of breaking down food into smaller particles is called ______.
The process of breaking down food into smaller particles is called ______.
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Match the following parts of the digestive tract with their functions:
Match the following parts of the digestive tract with their functions:
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Which of the following is NOT a component of the digestive tract?
Which of the following is NOT a component of the digestive tract?
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The mucosa is the outermost layer of the digestive tract wall.
The mucosa is the outermost layer of the digestive tract wall.
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Which mesentery connects the lesser curvature of the stomach to the liver?
Which mesentery connects the lesser curvature of the stomach to the liver?
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The soft palate is the anterior part of the roof of the oral cavity.
The soft palate is the anterior part of the roof of the oral cavity.
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What enzyme found in saliva helps to break down carbohydrates?
What enzyme found in saliva helps to break down carbohydrates?
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The tongue houses taste buds and ______.
The tongue houses taste buds and ______.
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Match the following types of teeth with their general functions:
Match the following types of teeth with their general functions:
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Which of the following is NOT one of the three major salivary glands?
Which of the following is NOT one of the three major salivary glands?
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Humans have enzymes that can digest cellulose.
Humans have enzymes that can digest cellulose.
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What condition occurs when gastric juices regurgitate into the esophagus?
What condition occurs when gastric juices regurgitate into the esophagus?
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Saliva is secreted approximately _______ liters per day.
Saliva is secreted approximately _______ liters per day.
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Which of the following best describes the primary function of the large intestine?
Which of the following best describes the primary function of the large intestine?
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The ileocecal junction connects the large intestine to the rectum.
The ileocecal junction connects the large intestine to the rectum.
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What structure is attached to the cecum in the large intestine?
What structure is attached to the cecum in the large intestine?
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Micelles are formed by bile salts surrounding ______ and ______ during lipid digestion.
Micelles are formed by bile salts surrounding ______ and ______ during lipid digestion.
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Match the digestive processes with their descriptions:
Match the digestive processes with their descriptions:
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What initiates the swallowing reflex?
What initiates the swallowing reflex?
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The stomach can hold up to 1 liter of food.
The stomach can hold up to 1 liter of food.
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What is the paste-like substance that forms when food begins to be broken down in the stomach?
What is the paste-like substance that forms when food begins to be broken down in the stomach?
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The thick, ring of smooth muscle around the pyloric opening is called the ______.
The thick, ring of smooth muscle around the pyloric opening is called the ______.
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Match the following stomach secretions with their functions:
Match the following stomach secretions with their functions:
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Which of the following statements about peristalsis is true?
Which of the following statements about peristalsis is true?
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Intrinsic factor is important for the absorption of vitamin B12.
Intrinsic factor is important for the absorption of vitamin B12.
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What phase of stomach secretion is initiated by the sight, smell, taste, or thought of food?
What phase of stomach secretion is initiated by the sight, smell, taste, or thought of food?
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The large folds in the stomach that allow it to stretch are called ______.
The large folds in the stomach that allow it to stretch are called ______.
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What is the primary role of hydrochloric acid in the stomach?
What is the primary role of hydrochloric acid in the stomach?
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Which phase of stomach secretion is stimulated by partially digested proteins and stomach distention?
Which phase of stomach secretion is stimulated by partially digested proteins and stomach distention?
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The small intestine measures approximately 3 meters in length.
The small intestine measures approximately 3 meters in length.
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What is the primary function of the small intestine?
What is the primary function of the small intestine?
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The first part of the small intestine is called the __________.
The first part of the small intestine is called the __________.
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Match the sections of the small intestine with their characteristics:
Match the sections of the small intestine with their characteristics:
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What stimulates the intestinal phase of gastric secretion?
What stimulates the intestinal phase of gastric secretion?
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Peristaltic waves in the stomach help to mix food thoroughly to form chyme.
Peristaltic waves in the stomach help to mix food thoroughly to form chyme.
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What do goblet cells in the small intestine produce?
What do goblet cells in the small intestine produce?
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The mucosa of the small intestine is primarily composed of __________ epithelium.
The mucosa of the small intestine is primarily composed of __________ epithelium.
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When does the stomach typically empty after a regular meal?
When does the stomach typically empty after a regular meal?
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Study Notes
Digestive System Overview
- The digestive system comprises the digestive tract (also known as the gastrointestinal tract) and associated organs.
- The digestive tract is a continuous tube extending from the mouth to the anus.
- The primary functions of the digestive system include ingestion, mastication, propulsion, mixing, digestion, secretion, absorption, and elimination.
Topic Learning Outcomes
- List the major functions of the digestive system.
- Describe the general histology of the digestive tract.
- Describe the parts and their major functions of the digestive tract.
- Describe the anatomy, physiology, histology, and ducts of the liver and pancreas.
- Describe the digestion, absorption, and transport of carbohydrates, lipids, and proteins.
- Discuss water movement into and out of the digestive tract.
- Describe the effects of aging on the digestive system.
Digestive System Functions
- Ingestion and mastication of solids and liquids.
- Propulsion and mixing.
- Digestion and secretion.
- Absorption.
- Elimination.
Digestive System Components (Organs)
- Oral Cavity (Mouth)
- Pharynx (Throat)
- Esophagus
- Stomach
- Small Intestines
- Large Intestines
- Rectum
- Anus
- Salivary Glands
- Liver
- Gallbladder
- Pancreas
Layers of Digestive Tract Wall
- Mucosa (innermost layer; secretes mucus)
- Submucosa (above mucosa; contains blood vessels, nerves, and small glands)
- Muscularis (above submucosa; contains longitudinal, circular, and oblique muscles)
- Serosa/Adventitia (outermost layer; serosa when covered with peritoneum, adventitia otherwise)
Peritoneum and Mesenteries
- Peritoneum: smooth epithelial layer (serous membranes: visceral and parietal peritoneum)
- Mesenteries: connective tissue of organs within the abdominal cavity
- Specific Mesenteries:
- Lesser Omentum: mesentery connecting lesser curvature of stomach to liver and diaphragm.
- Greater Omentum: mesentery connecting greater curvature of stomach to transverse colon and posterior body wall.
Oral Cavity
- First part of the digestive system.
- Contains stratified squamous epithelium.
- Salivary glands produce saliva containing enzymes to breakdown carbohydrates into glucose.
- Saliva cleanses the mouth and moistens food.
- Amylase: salivary enzyme breaking down carbohydrates.
- Lysozyme: salivary enzyme active against bacteria.
- Tongue: houses taste buds and mucus.
Teeth
- Normal adults have 32 teeth.
- Primary teeth (baby teeth) number 20.
- Teeth are composed of enamel, dentin, pulp cavity, and root.
- Teeth are anchored in alveolar bone.
- Cavities are caused by the breakdown of enamel by acids from bacteria.
- The palate is the roof of the oral cavity. It consists of a hard palate and a soft palate.
Salivary Glands
- Parotid, submandibular, and sublingual glands.
- Produce saliva (a mixture of serous and mucous fluids) with enzymes for food breakdown.
- Parotid glands are the largest.
- Submandibular glands secrete more serous than mucus.
- Sublingual glands primarily secrete mucus.
- Mumps is an inflammation of the parotid gland.
Secretions of Oral Cavity
- Saliva is secreted about 0.5-1.5 liters per day.
- Salivary amylase works on starch and other polysaccharides, producing maltose and isomaltose (sweet taste).
- Humans lack enzymes to digest cellulose.
- Mastication is the chewing and breaking down of food into smaller particles by teeth.
Pharynx (Throat)
- Connects the mouth to the esophagus.
- Three parts: nasopharynx, oropharynx, and laryngopharynx.
Esophagus
- Tube connecting the pharynx to the stomach.
- Transports food to the stomach.
- Heartburn occurs when gastric juices regurgitate into the esophagus, often caused by caffeine, smoking, or excess eating/drinking.
- Swallowing involves three phases: voluntary, pharyngeal, and esophageal.
Swallowing
- Voluntary phase: bolus forms in the mouth and is pushed into the oropharynx.
- Pharyngeal phase: swallowing reflex initiated when bolus stimulates receptors in oropharynx.
- Esophageal phase: food moves from pharynx to stomach via peristalsis.
- Peristalsis: wave-like contractions pushing food through the digestive tract.
Stomach
- Located in the abdomen.
- Storage tank for food (up to 2 liters).
- Produces mucus, hydrochloric acid (HCl), and protein-digesting enzymes.
- Contains a layer of mucus to protect tissues from acidic environment.
- Three muscular layers facilitate churning.
- Rugae are folds that enable expansion.
- Chyme is the paste-like substance formed when food begins to be broken down.
- Pyloric sphincter controls passage of chyme into small intestine.
- Hunger pangs are contractions related to low blood glucose
- Stomach is involved in the three phases (Cephalic, Gastric, Intestinal) of stomach secretions regulation (using hormones and neurons)
Secretion of the Stomach
- Acidic chyme (containing mucus, HCl, intrinsic factor, pepsinogen, and gastrin) is produced during the gastric phase when partially digested proteins and stomach distention prompt the process
Regulation of Stomach Secretions
- Cephalic phase: initiated by sight, smell, taste, or thought of food.
- Gastric phase: partially digested proteins and stomach distension prompt secretion.
- Intestinal phase: acidic chyme stimulates neural reflexes and hormone release (e.g., secretin and cholecystokinin) that inhibit further gastric secretions.
Movement in the Stomach
- Mixing waves: weak contractions mix food to form chyme.
- Peristaltic waves: stronger contractions force chyme toward and through the pyloric sphincter.
Small Intestine
- Measures 6 meters in length.
- Major absorptive organ.
- Chyme takes 3-5 hours to pass through.
- Contains enzymes to further breakdown food.
- Contains secretions to protect against the acidity of chyme.
- Three parts: duodenum (first part; 25 cm), jejunum (second part; 2.5 meters), ileum (third part; 3.5 meters).
Parts of Small Intestine
- Duodenum: first part (25 cm); contains absorptive cells, goblet cells, granular cells, endocrine cells, bile and pancreatic ducts.
- Jejunum: second part (2.5 meters); primary site for nutrient absorption.
- Ileum: third part (3.5 meters).
Mucosa of the Small Intestine
- Simple columnar epithelium with four major cell types.
- Absorptive cells: have microvilli, produce digestive enzymes, and absorb digested food.
- Goblet cells: produce protective mucus.
- Granular cells: potentially help protect intestinal epithelium from bacteria.
- Endocrine cells: produce regulatory hormones.
Mucosa of the Small Intestine (Specialized)
- Intestinal glands (crypts of Lieberkühn): tubular glands in the mucosa at the base of villi
- Granular and endocrine cells are at the bottom of the glands
- Duodenum has duodenal glands in the submucosa, opening into the base of intestinal glands
Secretions of the Small Intestine
- Secretion of small intestine consists primarily of mucus, ions, and water.
- Peptidases, disaccharidases are enzymes breaking down proteins into amino acids, disaccharides into monosaccharides
Movement in Small Intestine
- Mixing and propulsion of chyme occur through peristalsis(along the length of the intestine) and segmental contractions (mixing intestinal contents)
Ileocecal Sphincter(Small and Large Intestines)
- Muscle at the junction of small and large intestines keeps it mildly contracted most of the time.
- Peristaltic contractions from small intestine cause the sphincter to relax, and chyme moves into the cecum.
- Prevents movement from large intestine back into small intestine
Segmental Contractions in Small Intestine
- Secretion introduced to the digestive tract begins in one spot.
- Segments of tract alternate between contraction and relaxation.
- Material spreads out in both directions from introduction point.
- Results in more diffuse mixture within digestive tract.
Liver Anatomy
- Located in the upper right quadrant of the abdomen.
- Divided into lobes: right, left, quadrate, and caudate.
- Covered by visceral peritoneum (serous membrane).
- Contains hepatic ducts, hepatic portal vein, hepatic artery, and gallblader
Liver Ducts
- Hepatic ducts: transport bile out of the liver
- Common hepatic duct: created from left and right hepatic ducts.
- Cystic duct: joins common hepatic duct; extends from gallbladder
- Common bile duct: formed from common hepatic duct and cystic duct
Bile and Pancreatic Secretions
- Hepatic ducts, combining to form a common hepatic duct that merges with the cystic duct to form a common bile duct which reaches the duodenum
- Accessory pancreatic duct empties into duodenum
- Pancreatic secretions can also enter duodenum via pancreatic duct
Functions of Liver
- Digestive and excretory functions.
- Stores and processes nutrients.
- Detoxifies harmful chemicals.
- Synthesizes new molecules.
- Secretes 700 milliliters of bile daily.
- Bile neutralizes stomach acid, breaks down fats.
Control of Bile Secretion and Release
- Vagus nerve stimulation causes gallbladder contraction and bile release into duodenum.
- Secretin from duodenum stimulates liver bile secretion.
- Cholecystokinin from duodenum stimulates gallbladder contraction and sphincter relaxation, releasing bile into duodenum.
- Bile salts also stimulate bile secretion.
Pancreas
- Located posterior to the stomach, inferior to the upper left quadrant.
- Consists of head, body, and tail.
- Tail touches the spleen.
- Endocrine tissues: pancreatic islets produce insulin and glucagon. Insulin increases glucose uptake, glucagon releases glucose (primarily in liver).
- Exocrine tissues: produce digestive enzymes (e.g., trypsin, chymotrypsin, carboxypeptidase, amylase, lipase, nucleases) that travel through ducts.
Pancreatic Secretions
- Major protein-digesting enzymes: trypsin, chymotrypsin, carboxypeptidase
- Pancreatic amylase continues polysaccharide digestion (started in mouth)
- Pancreatic lipase is a lipid-digesting enzyme
- Pancreatic nucleases degrade DNA/RNA to their component nucleotides.
Large Intestine
- Function: absorbs water from indigestible food.
- Components: cecum, colon (ascending, transverse, descending, sigmoid), rectum, anal canal.
- Cecum: joins small intestine at ileocecal junction. Appendix attached.
- Colon: 1.5 meters long
- Rectum: straight tube from sigmoid colon to anal canal.
- Anal canal: last 2-3 cm of digestive tract.
- Food takes 18-24 hours to pass through.
- Feces are product of water, indigestible food, and microbes.
- Microbes synthesize vitamin K inside large intestine.
Digestive Process
- Digestion: food breakdown in stomach and mouth
- Propulsion: moves food through digestive tract (swallowing and peristalsis)
- Absorption: primarily in duodenum and jejunum of small intestine.
- Defecation: elimination of waste (feces).
Digestion
- Food is broken down into carbohydrates (monosaccharides), lipids (fatty acids and monoglycerides), and proteins (amino acids).
Protein Digestion
- Pepsin: protein-digesting enzyme secreted by the stomach.
- Trypsin, chymotrypsin, carboxypeptidase: protein-digesting enzymes secreted by pancreas (in inactive form) and activated in the small intestine.
- Peptidases: small intestine enzymes breaking down peptides into tripeptides.
- Absorption of tripeptides, dipeptides, or individual amino acids occurs through intestinal epithelial cells (via cotransport).
Water and Minerals
- Water can move across the intestinal wall in either direction depending on osmotic pressures.
- 99% of water entering the intestine is absorbed.
- Minerals are actively transported across the small intestine wall.
Fluid Volumes in Digestive Tract
- Varies among substances and parts of the digestive tract (e.g., salivary glands secrete 1L, bile 0.7L, small intestine secretions measure 2L, etc.)
- About 92% of absorbed fluids are in small intestines, 6%-7% in large intestine
- Fecal water amount is 1% or less of total fluid consumed / secreted
Summary
- The presented notes summarize a wide variety of information about the human digestive system. Each part including major functions, components, and processes throughout the anatomical structures.
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Description
Test your knowledge of the digestive system with this quiz covering its anatomy and functions. From the roles of different organs to the types of teeth, explore various aspects of human digestion. Challenge yourself with questions on enzymes, layers of the digestive tract, and more.
