Two Groups of Organs:
Alimentary Canal (GI Tract): Runs from mouth to anus; responsible for digesting food and absorbing nutrients. Includes:
Mouth
Pharynx
Esophagus
Stomach
Small Intestine
Large Intestine
Accessory Digestive Organs: Assist digestion but are not part of the GI tract. Include:
Teeth
Tongue
Gallbladder
Digestive Glands: Salivary glands, liver, pancreas.
Six Essential Activities:
Ingestion: Taking in food.
Propulsion: Movement of food through the GI tract, including:
Peristalsis: Wave-like muscle contractions moving food along.
Segmentation: Contractions of non-adjacent segments, mixing food.
Mechanical Breakdown: Physical process of chewing and churning.
Digestion: Chemical breakdown of food into absorbable molecules.
Absorption: Movement of nutrients from the GI tract into the blood.
Defecation: Elimination of indigestible substances.
Sensory Receptors: Mechanoreceptors and chemoreceptors respond to:
Stretch
Changes in osmolarity & pH
Presence of food
Intrinsic and Extrinsic Controls:
Short Reflexes: Local enteric nervous system control.
Long Reflexes: CNS involvement, responds to stimuli.
Peritoneum: Serous membrane; has two layers:
Visceral Peritoneum: Covers digestive organs.
Parietal Peritoneum: Lines abdominal wall.
Peritoneal Cavity: Space between the two layers containing fluid to lubricate organs.
Major Arteries: Branches from the aorta supplying digestive organs:
Hepatic, splenic, left gastric arteries
Inferior and superior mesenteric arteries
Hepatic Portal Circulation: Drains nutrient-rich blood from digestive organs to the liver.
Four Basic Layers:
Mucosa: Lines the lumen; functions in secretion, absorption, and protection.
Submucosa: Areolar connective tissue containing blood vessels and nerves.
Muscularis Externa: Segmentation and peristalsis.
Serosa: Outermost layer; protective.
Types of Motility:
Peristalsis: Wave-like movements propel contents.
Segmentation: Back-and-forth mixing of food.
Rate of Contraction: Influenced by hormonal signals and local stimuli.
Functions: Temporary storage, digestion into chyme.
Gastric Juice Composition: Contains hydrochloric acid (HCl), pepsinogen (inactive enzyme for protein digestion).
Mucosal Barrier: Protects stomach lining from acid.
Major Site for Digestion and Absorption: Nutrients absorbed within 3-6 hours.
Structural Modifications:
Circular Folds: Slow down chyme movement for efficiency.
Villi: Increase surface area; contain capillary beds for nutrient absorption.
Microvilli: Further increase surface area and contain enzymes.
Carbohydrates: Monosaccharides absorbed; enzymes involved include salivary and pancreatic amylases.
Proteins: Digested by pepsin in the stomach; pancreatic enzymes continue digestion in the small intestine.
Lipids: Emulsified by bile; broken down by pancreatic lipases.
Nucleic Acids: Digested by pancreatic enzymes; absorbed as nucleotide monomers.
Causes: Anything affecting bile/pancreatic juice delivery, or intestinal mucosa integrity.
Celiac Disease: Immune reaction to gluten causing intestinal damage; requires dietary adjustments.
Absorption: Water, electrolytes, and the formation of feces; bacterial flora contribute to vitamin production.
Motility: Slow contractions and mass movements propagated by the gastrocolic reflex when food is present.
Reflex Action: Contraction of sigmoid colon and rectum; relaxation of anal sphincters controlled voluntarily.
Assisted by Valsalva Maneuver: Increased abdominal pressure aids in expulsion.
Digestive System Overview
Two Groups of Organs:
Alimentary Canal (GI Tract): Runs from mouth to anus; responsible for digesting food and absorbing nutrients. Includes:
Mouth
Pharynx
Esophagus
Stomach
Small Intestine
Large Intestine
Accessory Digestive Organs: Assist digestion but are not part of the GI tract. Include:
Teeth
Tongue
Gallbladder
Digestive Glands: Salivary glands, liver, pancreas.
Digestive Processes
Six Essential Activities: 1. Ingestion: Taking in food.
Propulsion: Movement of food through the GI tract, including:
Peristalsis: Wave-like muscle contractions moving food along.
Segmentation: Contractions of non-adjacent segments, mixing food.
Mechanical Breakdown: Physical process of chewing and churning.
Digestion: Chemical breakdown of food into absorbable molecules.
Absorption: Movement of nutrients from the GI tract into the blood.
Defecation: Elimination of indigestible substances.
Regulatory Mechanisms of GI Tract
Sensory Receptors: Mechanoreceptors and chemoreceptors respond to:
Stretch
Changes in osmolarity & pH
Presence of food
Intrinsic and Extrinsic Controls:
Short Reflexes: Local enteric nervous system control.
Long Reflexes: CNS involvement, responds to stimuli.
Peritoneum and Peritoneal Cavity
Peritoneum: Serous membrane; has two layers:
Visceral Peritoneum: Covers digestive organs.
Parietal Peritoneum: Lines abdominal wall.
Peritoneal Cavity: Space between the two layers containing fluid to lubricate organs.
Blood Supply: Splanchnic Circulation
Major Arteries: Branches from the aorta supplying digestive organs:
Hepatic, splenic, left gastric arteries
Inferior and superior mesenteric arteries
Hepatic Portal Circulation: Drains nutrient-rich blood from digestive organs to the liver.
Histology of the Alimentary Canal
Four Basic Layers:
Mucosa: Lines the lumen; functions in secretion, absorption, and protection.
Epithelium: Different types of cells line the digestive tract; changes from simple squamous in the esophagus to simple columnar in the stomach and intestines.
Goblet cells: Secrete mucus, which lubricates and protects the lining.
Submucosa: Areolar connective tissue containing blood vessels and nerves.
Muscularis Externa: Segmentation and peristalsis.
Serosa: Outermost layer; protective.
Motility of Digestive Processes
Types of Motility:
Peristalsis: Wave-like movements propel contents.
Segmentation: Back-and-forth mixing of food.
Rate of Contraction: Influenced by hormonal signals and local stimuli.
Digestion in the Stomach
Functions: Temporary storage, digestion into chyme.
Gastric Juice Composition: Contains hydrochloric acid (HCl), pepsinogen (inactive enzyme for protein digestion).
Gastric Pits: Contain specialized cells:
Parietal cells: Secrete HCl and intrinsic factor.
Chief cells: Secrete pepsinogen and gastric lipase.
Mucous cells: Secrete mucus to protect the stomach lining from acid.
Mucosal Barrier: Protects stomach lining from acid.
Digestion in the Small Intestine
Major Site for Digestion and Absorption: Nutrients absorbed within 3-6 hours.
Structural Modifications:
Circular Folds: Slow down chyme movement for efficiency.
Villi: Increase surface area; contain capillary beds for nutrient absorption.
Microvilli: Further increase surface area and contain enzymes.
Absorption of Nutrients
Carbohydrates: Monosaccharides absorbed; enzymes involved include salivary and pancreatic amylases.
Proteins: Digested by pepsin in the stomach; pancreatic enzymes continue digestion in the small intestine.
Lipids: Emulsified by bile; broken down by pancreatic lipases.
Nucleic Acids: Digested by pancreatic enzymes; absorbed as nucleotide monomers.
Malabsorption Conditions
Causes: Anything affecting bile/pancreatic juice delivery, or intestinal mucosa integrity.
Celiac Disease: Immune reaction to gluten causing intestinal damage; requires dietary adjustments.
Large Intestine Functions
Absorption: Water, electrolytes, and the formation of feces; bacterial flora contribute to vitamin production.
Motility: Slow contractions and mass movements propagated by the gastrocolic reflex when food is present.
Defecation Process
Reflex Action: Contraction of sigmoid colon and rectum; relaxation of anal sphincters controlled voluntarily.
Assisted by Valsalva Maneuver: Increased abdominal pressure aids in expulsion.