Digestive System Functions and Activities PDF

(PART 1) Digestive System Overview Digestive System Components: ○ Digestive tract (alimentary canal): Tube from mouth to anus. ○ Accessory organs: Glands located outside the GI tract aiding digestion and absorption (e.g., liver, pancreas, gallbladder...

(PART 1) Digestive System Overview Digestive System Components: ○ Digestive tract (alimentary canal): Tube from mouth to anus. ○ Accessory organs: Glands located outside the GI tract aiding digestion and absorption (e.g., liver, pancreas, gallbladder). Digestive Tract Structure Main Parts: ○ Oral cavity (mouth) ○ Pharynx (throat) ○ Esophagus ○ Stomach ○ Small intestine ○ Large intestine ○ Anus Layers of the Alimentary Canal Mucosa: ○ Innermost layer. ○ Contains mucous epithelium, lamina propria, and muscularis mucosa. Submucosa: ○ Beneath mucosa. ○ Contains blood vessels, nerves, and lymphatics. ○ Includes submucosal plexus (nerve cells stimulating gland secretion). Muscularis: ○ Two layers (inner circular and outer longitudinal) except in the stomach. ○ Contains myenteric plexus (controls motility). Serosa:  ○ Outermost layer. ○ Part of the peritoneum (visceral peritoneum). Peritoneum Visceral Peritoneum: ○ Covers organs. Parietal Peritoneum: ○ Lines body wall. Retroperitoneal organs: ○ Covered by peritoneum on one surface (e.g., kidneys, pancreas). Mesenteries Function: ○ Hold abdominal organs in place. ○ Serve as pathways for vessels and nerves. Types: ○ Lesser omentum: Connects lesser curvature of the stomach to the liver and diaphragm. ○ Greater omentum: Connects greater curvature of the stomach to the transverse colon; stores fat. Oral Cavity Structures Lips (Labia): ○ Protect anterior mouth opening; orbicularis oris muscle. Cheeks: ○ Form lateral walls; buccinator muscle. Hard and Soft Palate: ○ Hard palate: Anterior roof. ○ Soft palate: Posterior roof. Uvula: ○ Fleshy projection at the back of the soft palate. Tongue: ○ Large muscular organ; attached at the back, free at the front. (PART 2) Accessory Organs of the Digestive System 1. Liver: ○ General Characteristics: Largest internal organ (~1.36 kg). Located in the right upper quadrant, inferior to the diaphragm. Composed of four lobes (two major: right and left, separated by the falciform ligament; two minor: caudate and quadrate visible from the posterior side). Contains a portal (porta hepatis) for vessels, ducts, and nerves. ○ Blood Supply: Hepatic Artery: Delivers oxygenated blood. Hepatic Portal Vein: Carries nutrient-rich blood from the digestive tract. Hepatic Veins: Drain deoxygenated blood from the liver to the inferior vena cava. ○ Liver Structure: Hepatic Cords: Composed of hepatocytes, radiating from the central vein. Hepatic Sinusoids: Found between cords, containing phagocytic Kupffer cells for detoxification. Bile Canaliculi: Transport bile from hepatocytes to the hepatic duct. ○ Functions: Bile Production: 600-1000 ml/day, neutralizes stomach acid, emulsifies fats. Storage: Glycogen, lipids, vitamins, copper, and iron. Synthesis: Blood proteins (albumins, fibrinogen, globulins, heparin, clotting factors). Nutrient Conversion: Converts amino acids to glucose and activates vitamin D. Detoxification: Converts toxic ammonia to urea for excretion.  Phagocytosis: Kupffer cells remove old blood cells and bacteria. 2. Gallbladder: ○ Location: Small sac on the liver's inferior surface. ○ Function: Stores and concentrates bile produced by the liver. ○ Bile Flow: Exits via the cystic duct, joins with the common hepatic duct to form the common bile duct, which leads to the duodenum. Stimulation: Cholecystokinin triggers gallbladder contraction to release bile during digestion. ○ Concentration: Bile becomes more effective when concentrated but can form stones if overly dehydrated. 3. Bile Pathway: ○ Production: In the liver. ○ Flow: Right/left hepatic ducts → common hepatic duct → cystic duct (for storage in the gallbladder). ○ Release: From the gallbladder via the cystic duct to the common bile duct and then to the duodenum during digestion. (PART 3) Digestive System Functions and Activities 1. Ingestion: ○ The process of taking food into the mouth (oral cavity). 2. Mastication (Chewing): ○ Breakdown of large particles via mechanical digestion to aid chemical digestion. ○ Teeth Roles: Incisors and canines: Cut food. Molars: Grind food. ○ Muscles Involved: Masseter, temporalis, medial pterygoid, lateral pterygoid (depresses mandible, opens jaw). 3. Swallowing (Deglutition): ○ Movement of bolus (food/liquid) from the mouth to the esophagus. ○ Phases: Voluntary Phase: Tongue moves bolus to pharynx. Pharyngeal Phase: Controlled by the medulla oblongata; soft palate elevates, upper esophageal sphincter relaxes, epiglottis tips to prevent food entry into the airway. Esophageal Phase: Peristalsis moves bolus to the stomach. 4. Propulsion: ○ Movement of food through the digestive tract (~24-36 hours). ○ Peristalsis: Alternating contractions push food. ○ Mass Movements: Strong contractions in the large intestine moving contents to the anus. 5. Mixing: ○ Segmental contractions mix food with secretions to form chyme in the small intestine. 6. Secretions: ○ Mucus: Lubricates and protects the GI tract. ○ Water: Aids in food liquefaction for digestion/absorption. ○ Bile: Emulsifies fats for digestion. ○ Enzymes: Break down food chemically. 7. Digestion Types: ○ Mechanical Digestion: Physical breakdown (e.g., chewing, stomach churning, segmentation). ○ Chemical Digestion: Enzyme-driven breakdown (e.g., carbohydrates to glucose). 8. Carbohydrate Digestion: ○ Starts in the mouth with salivary amylase, continues in the duodenum with pancreatic amylase, and completes with disaccharidases breaking down into monosaccharides. 9. Lipid Digestion: ○ Limited activity in the mouth/stomach due to lack of emulsification. ○ Bile in the duodenum facilitates breakdown by pancreatic lipase into fatty acids and monoglycerides. 10. Protein Digestion: ○ Starts in the stomach with pepsin. ○ Pancreatic enzymes (trypsin, chymotrypsin, carboxypeptidase) act in the small intestine, breaking proteins into peptides and further into amino acids by peptidases.