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Questions and Answers
What is the primary function of the large intestine?
What is the primary function of the large intestine?
Which hormone stimulates the release of bile from the gallbladder?
Which hormone stimulates the release of bile from the gallbladder?
What do bile salts primarily aid in?
What do bile salts primarily aid in?
Which process describes the cycling of bile salts from the liver to the small intestine and back?
Which process describes the cycling of bile salts from the liver to the small intestine and back?
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What is the composition of bile primarily made up of?
What is the composition of bile primarily made up of?
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What happens when the rectum is distended?
What happens when the rectum is distended?
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Which region of the large intestine is responsible for collecting material from the ileum?
Which region of the large intestine is responsible for collecting material from the ileum?
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What role does saliva play in the immune system?
What role does saliva play in the immune system?
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Which enzyme is primarily involved in the breakdown of lipids?
Which enzyme is primarily involved in the breakdown of lipids?
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What is a significant age-related change affecting the gastrointestinal tract?
What is a significant age-related change affecting the gastrointestinal tract?
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What is the primary function of the digestive system?
What is the primary function of the digestive system?
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What layer of the digestive tract contains the submucosal nerve plexus?
What layer of the digestive tract contains the submucosal nerve plexus?
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Which type of muscle is predominantly found in the muscular layer of the digestive system?
Which type of muscle is predominantly found in the muscular layer of the digestive system?
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What role does the peritoneal fluid play in the peritoneal cavity?
What role does the peritoneal fluid play in the peritoneal cavity?
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What is the function of mesenteries in the digestive system?
What is the function of mesenteries in the digestive system?
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Which mechanism allows food to be propelled through the GI tract?
Which mechanism allows food to be propelled through the GI tract?
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What triggers the waves of contraction in the gastric motility control?
What triggers the waves of contraction in the gastric motility control?
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Which of the following conditions is characterized by inflammation of the peritoneum?
Which of the following conditions is characterized by inflammation of the peritoneum?
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What is the role of enteroendocrine cells in the digestive system?
What is the role of enteroendocrine cells in the digestive system?
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The greater omentum is classified as which type of membrane in the digestive system?
The greater omentum is classified as which type of membrane in the digestive system?
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What is the primary function of the jejunum?
What is the primary function of the jejunum?
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Which hormone is released when chyme enters the duodenum and stimulates the release of pancreatic enzymes?
Which hormone is released when chyme enters the duodenum and stimulates the release of pancreatic enzymes?
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Which component is secreted by goblet cells in the small intestine?
Which component is secreted by goblet cells in the small intestine?
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What is the primary blood supply for the small intestine?
What is the primary blood supply for the small intestine?
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Which cell type in the pancreas is responsible for the secretion of insulin?
Which cell type in the pancreas is responsible for the secretion of insulin?
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What is the role of enterochromaffin cells in the intestines?
What is the role of enterochromaffin cells in the intestines?
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What triggers the secretion of pancreatic juices?
What triggers the secretion of pancreatic juices?
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What is the function of the circular folds in the small intestine?
What is the function of the circular folds in the small intestine?
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Which structure in the liver allows large and small particles to enter?
Which structure in the liver allows large and small particles to enter?
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What type of tissue forms the structure of the liver lobules?
What type of tissue forms the structure of the liver lobules?
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How does secretin affect gastric motility?
How does secretin affect gastric motility?
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What type of cells secrete pancreatic alpha-amylase?
What type of cells secrete pancreatic alpha-amylase?
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Which of the following functions is not associated with the liver?
Which of the following functions is not associated with the liver?
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Which section of the small intestine is primarily responsible for neutralizing chyme?
Which section of the small intestine is primarily responsible for neutralizing chyme?
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Which structure primarily protects the esophagus from stomach acid?
Which structure primarily protects the esophagus from stomach acid?
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What is one function of ghrelin in the digestive system?
What is one function of ghrelin in the digestive system?
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What is the main role of the uvula during the swallowing process?
What is the main role of the uvula during the swallowing process?
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Which layer of the stomach aids in the movement and churning of contents?
Which layer of the stomach aids in the movement and churning of contents?
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Which type of saliva is primarily secreted by the parotid glands?
Which type of saliva is primarily secreted by the parotid glands?
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What initiates the pharyngeal phase of swallowing?
What initiates the pharyngeal phase of swallowing?
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What substance is produced by chief cells in the gastric pits?
What substance is produced by chief cells in the gastric pits?
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What substance is primarily responsible for maintaining the acidic environment in the stomach?
What substance is primarily responsible for maintaining the acidic environment in the stomach?
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Why is the submucosa of the esophagus important?
Why is the submucosa of the esophagus important?
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Which of the following is NOT a function of saliva?
Which of the following is NOT a function of saliva?
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What is the primary role of the rugae in the stomach?
What is the primary role of the rugae in the stomach?
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Which type of drug can be absorbed in the stomach, potentially causing GI bleeding with excessive exposure?
Which type of drug can be absorbed in the stomach, potentially causing GI bleeding with excessive exposure?
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What stimulates the release of cholecystokinin in response to food in the duodenum?
What stimulates the release of cholecystokinin in response to food in the duodenum?
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Which cranial nerve is responsible for controlling the movement of the tongue?
Which cranial nerve is responsible for controlling the movement of the tongue?
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Study Notes
Digestive System Functions
- The digestive system breaks down food into absorbable organic molecules (carbohydrates, fats, proteins), absorbs nutrients, and eliminates wastes.
- The digestive tract lining protects the body from corrosive substances and ingested pathogens.
- Ingestion: Food intake into the oral cavity.
- Digestion and propulsion involve mechanical churning (mechanical digestion aiding chemical digestion) and chemical breakdown by enzymes and digestive juices.
- Smaller molecules like glucose absorb easily, but larger molecules (proteins) need enzyme breakdown.
- Propulsion moves material through the digestive tract.
- Secretions provide enzymes and substances for chemical digestion.
- Absorption takes up organic/inorganic nutrients and water.
- Defecation eliminates waste products.
Histology of the Digestive Tract
- The digestive tract has four major layers:
- Mucosa: Innermost layer with epithelium (simple or stratified), lamina propria (connective tissue with vessels/nerves), and muscularis mucosae (smooth muscle).
- Submucosa: Dense irregular connective tissue binding mucosa to muscular layer; contains submucosal nerve plexus. Rich in blood and lymphatic vessels.
- Muscular layer: Smooth muscles (circular and longitudinal) for mechanical digestion; contains myenteric nerve plexus.
- Serosa: Serous membrane (visceral peritoneum) covering most parts; adventitia supports areas outside the peritoneum.
Peritoneum and Mesenteries
- The peritoneal cavity is lined by the peritoneum (serous membrane).
- Two parts: Visceral peritoneum (covers organs), parietal peritoneum (lines abdominal/pelvic cavity walls).
- Peritoneal fluid reduces friction.
- Retroperitoneal structures lie behind the peritoneum.
- Mesenteries are double-layered serous membranes stabilizing organs and associated vessels.
- Lesser omentum: Connects stomach to liver.
- Greater omentum: Connects stomach to intestines, functions as a protective sheet.
- Mesentery proper & Mesocolon.
Control of Gastric Motility
- Gastric motility (movement) is controlled by:
- Local factors (stretch, pH change).
- Neural control (enteric nervous system, parasympathetic nervous system).
- Hormonal influences (e.g., ghrelin, cholecystokinin).
- Pacesetting cells initiate rhythmic contractions (peristalsis) moving food through the tract.
- Segmentation churns food as it moves.
Oral Cavity
- The oral cavity (mouth) is lined with oral mucosa (stratified squamous epithelium).
- Functions:
- Sensation, mechanical digestion (mastication), lubrication, and chemical digestion (salivary amylase).
- The uvula helps prevent food from entering the nasal passages.
- Some lipid-soluble drugs (e.g., nitroglycerin) can be absorbed through the tongue's mucosa.
Tongue
- Functions: Mechanical digestion, food manipulation, sensory analysis (taste, temperature), secretion of mucins and lingual lipase.
- Lingual papillae are projections on the tongue's surface.
- Lingual frenulum can affect tongue movement.
Teeth
- Teeth (or dentition) consist primarily of dentin.
- Enamel protects biting surfaces.
- Two sets: Deciduous (baby teeth) and permanent (adult teeth).
- Dental health affects overall health.
Saliva and Salivary Glands
- Saliva lubricates, moistens, dissolves chemicals for taste, and initiates digestion (salivary amylase).
- Saliva cleanses the mouth.
- Three major salivary glands: Parotid (salivary amylase), sublingual (mucus), and submandibular (mixture of mucus, buffers and salivary amylase).
From Oral Cavity to Stomach
- Food forms a bolus in the oral cavity.
- Pharyngeal muscles propel food to the esophagus.
- Epiglottis prevents food from entering the trachea.
Esophagus
- Approx. 25 cm long, tube carrying food.
- Passes through the esophageal hiatus in the diaphragm.
- Lined with stratified squamous epithelium.
- Folded mucosa/submucosa for expansion during swallowing.
Swallowing (Deglutition)
- Three phases: Buccal, pharyngeal, and esophageal.
- Swallowing reflex is initiated by sensory receptors in the mouth and pharynx.
Stomach
- Located in the left upper quadrant.
- J-shaped organ for food storage & digestion.
- Rugae allow for expansion.
- Mechanical and chemical digestion occur.
- Chyme (mixed food and gastric secretions) is formed.
- Four regions: Cardia, fundus, body, pylorus.
Gastric Secretions
- Gastric glands secrete products into gastric pits
- Chief cells: Pepsinogen (activated to pepsin).
- Parietal cells: HCl (activates pepsin, kills microbes), Intrinsic factor (Vitamin B12 absorption).
- Enteroendocrine cells: Gastrin, histamine, somatostatin, and ghrelin (regulate stomach function).
Chemical Digestion in Stomach
- Salivary amylase and lingual lipase continue until pH falls below 4.5.
- Protein digestion begins when pH reaches ~2.0.
- Little nutrient absorption in stomach; some drugs (alcohol, aspirin) can be absorbed.
Regulation of Digestion
- Three phases of gastric control overlap:
- Cephalic phase (brain/sensory input).
- Gastric phase (distention, increased pH, protein).
- Intestinal phase (controls emptying rate, inhibits gastric motility).
Small Intestine
- Extends from pyloric sphincter to ileocecal valve.
- Divided into duodenum, jejunum, and ileum.
- Circular folds, villi, and microvilli increase absorptive surface area.
- Secretions include mucus and brush border enzymes (maltase, sucrase, lactase, etc).
- Peyer's patches (lymphoid tissue) are abundant in the ileum, part of the digestive system’s first line of defence against pathogens entering through the digestive tract.
Small Intestine (Continued)
- Secretion from intestinal glands include pancreatic and brush border enzymes. Lacteals absorb lipids.
- Interstitial hormones (gastrin, secretin, GIP, CCK, VIP, enterocrinin) regulate small intestine function and other digestive organs.
The Pancreas
- Endocrine (insulin, glucagon) and exocrine (pancreatic juices) functions.
- Pancreatic juices are an alkaline mix of enzymes, water, and ions.
- Enzymes break down food; fluids dilute and neutralize chyme.
- Pancreatic duct delivers secretions to the duodenum.
The Liver
- Largest visceral organ.
- Divided into lobules with hepatocytes.
- Blood supply from hepatic artery and hepatic portal vein.
- Function:
- Metabolic regulation, drug metabolism, hematological regulation (plasma protein, hormone/antibody removal), bile regulation.
Bile Duct System
- Bile flows from liver canaliculi to larger ducts, then leaves the liver by the right and left hepatic ducts which unit at the common hepatic duct, and through the cystic duct to the gallbladder for storage.
- Bile salts aid lipid digestion and absorption.
Gallbladder
- Stores and concentrates bile.
- CCK stimulates gallbladder contraction to release bile into the duodenum for lipid digestion and absorption.
Large Intestine
- Absorbs water; forms and expels feces.
- Divided into cecum, colon (ascending, transverse, descending, sigmoid), rectum, and anal canal.
- Lacks villi; contains abundant goblet cells for lubrication.
- Microbiome (bacteria) aids in vitamin synthesis.
- Defecation reflex controls elimination.
General Digestive Reminders
- Hydrolysis breaks down food molecules into smaller units (e.g., carbohydrates to monosaccharides).
- Lipids absorb as triglycerides in chylomicrons.
Immunity & the Digestive Tract
- The digestive tract has layers that have a protective function (mouth, rectum); saliva contains antibodies and lysosomes; lymphatic tissue (tonsils, Peyer's patch, appendix and Paneth cells) play a role in immunity.
Age-Related Changes
- Epithelial cell division declines; decreased smooth muscle tone weakens peristalsis and increases risk for injury and can lead to increased risk for cancer and dehydration.
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Description
Explore the key functions of the digestive system, including ingestion, digestion, absorption, and elimination of wastes. Learn about the histological layers of the digestive tract and their roles in protecting the body and aiding in digestion.
