Understanding Digestive System Anatomy and Functions

1. Digestive System Anatomy & Physiology

2. Function & Organization Function • The breakdown of food into small enough particles to be absorbed Organization • Alimentary Canal aka GI tract • Accessory Organs

3. Digestive Processes • Ingestion: bringing food into the system • Mechanical Digestion: the mechanical breakdown of food (chewing, mixing, churning) • Propulsion: movement of food through system

4. Digestive Processes • Chemical Digestion: breakdown of large food molecules by enzymes • Absorption: transport of digested food materials to the blood or lymph • Defecation: elimination of indigestible material from the body

5. Peritoneum • The largest serous membrane of the body lining all organs of the abdominal cavity and the cavity wall • Parietal peritoneum: lines walls • Visceral peritoneum: lines organs • Peritoneal cavity: potential space between membranes; produces serous fluid

6. Extensions of the Peritoneum • Falciform ligament: connects liver to anterior abdominal wall and diaphragm • Lesser omentum: attaches to medial stomach, attaching it to anterior wall

7. Extensions of the Peritoneum • Greater Omentum: extends off stomach; contains lymph nodes and holds fatty deposits • Mesentary: suspends coils of small intestine and attaches it to posterior abdominal wall

8. Wall Structure of Alimentary Canal • 4 layers • Mucosa/mucus membrane • Submucosa • Muscularis • Serosa

9. Wall Structure of Alimentary Canal 1. Mucosa: lines lumen of alimentary canal • Protects from microorganisms • Absorbs digested food materials • Secretes mucous & digestive enzymes

10. Wall Structure of Alimentary Canal 2. Submucosa -Rich in blood vessels, lymphatic vessels and nerve endings -Provides nourishment for tissues and carries away absorbed materials

11. Wall Structure of Alimentary Canal • Muscularis - smooth muscular layer (has 2 parts) • inner layer runs longitudinally • outer layer (constrictor layer) runs circularly • induces a propelling action called peristalsis

12. Wall Structure of Alimentary Canal 4. Serosa - visceral peritoneum -outermost covering of alimentary canal

13. Alimentary Canal: Mouth • Function: receives food and starts digestion and prepares it for swallowing - Teeth: performs mastication (chewing) - Uvula: fingerlike extension from archway; works with soft palate to close opening to nasal cavity upon swallowing

14. Mouth continued • Salivary Glands: accessory organs around mouth; secretes saliva • saliva: 99.5% water, 0.5% solutes • Lysozome: destroys bacteria • Salivary amylase: begins chemical digestion of carbohydrates • Mucus: lubricates and binds food particles to form a bolus

15. Alimentary Canal: Pharynx • Function: transports food from oral cavity to esophagus -uvula and epiglottis assist pharynx in transporting bolus to the esophagus ONLY

16. Alimentary Canal: Esophagus Function: 10 inch muscular tube that transports bolus to stomach from pharynx - Peristalsis: alternate waves of muscle contraction & relaxation; moves bolus along alimentary canal

17. Esophagus continued - Mucosa: made of stratified squamos epithelium to resist abrasion - Cardio-esophageal sphincter: found at distal end; acts as a valve to prevent stomach contents from entering esophagus

18. Alimentary Canal: Stomach • Function: c-shaped organ acting as a temporary storage site for food; performs mechanical and chemical digestion -Rugae: deep folds formed by inner lining of stomach when empty -Full stomach: can hold up to 1 gallon of food - Pyloric sphincter: valve that controls movement of food from stomach into small intestine

19. Stomach Wall • 4 basic layers: mucosa, submucosa, muscularis and serosa • Mucosa & muscularis is functionally and structurally different • Mucosa: gastric pits work to produce and secrete gastric juices • HCL, digestive enzymes and mucus

20. Stomach Wall • Muscularis • Stomach has an additional layer of muscle fibers • Allows stomach to churn and mix stomach contents

21. Stomach Functions • Mechanical Digestion: churning and mixing of stomach contents to aid digestion • Chemical Digestion: pepsin: breaks down proteins (works only in acidic environments)

22. Stomach Functions • Absorption: limited absorptive abilities (water, salts, glucose, alcohol, aspirin and some lipid-soluble drugs) • Propulsion: propels food into small intestine in the form of CHYME (mixture of food particles & gastric juice) • Chyme presses against pyloric sphincter causing it to relax and allowing chyme to pass

23. Alimentary Canal: Small Intestine • Completes mechanical and chemical digestion & is the main site of nutrient absorption • Propels food through with peristaltic waves • 20 feet long, highly coiled • Takes ~ 3-10 hours to move chyme through • Suspended to posterior abdominal wall via mesentary

24. Small Intestine continued 3 Segments: • Duodenum: receives chyme from stomach & digestive enzymes from accessory organs; about 10 inches long • Jejunum: site of absorption; about 8 feet long

25. Small Intestine continued • Ileum: about 12 feet long; the end of digestion and absorption of nutrients Ileocecal valve: the junction at which the small & large intestine join; sphincter muscle controlling the flow of material between organs

26. Wall of Small Intestine • Highly convoluted mucosa for better absorption through increased surface area • Intestinal villi: tiny projections of mucosa • Microvilli: even smaller projections on the intestinal villi

27. Wall of Small Intestine • Within each villi is: • Blood capillaries • Lacteals (lymphatic vessels) - Act to carry absorbed nutrients away

28. Alimentary Canal: Large Intestine • Final segment of alimentary canal • ~5 feet long but larger in diameter than small intestine • Function: to dry out indigestible material by absorbing water; eliminate unwanted materials

29. Large Intestine continued • 5 main segments of large intestine • Cecum: sac-like pouch receiving material from ileum • Vermiform appendix: worm-like extension holding lymphatic tissue • Colon: ascending, transverse, descending, sigmoid • Rectum • Anus

30. Large Intestine continued Anus: has 2 sphincters • Internal: involuntary; told to relax when fecal matter stimulates the defecation reflex in the rectum • External: voluntary; if relaxed, elimination occurs

31. Fecal Formation • Fecal matter: 75% water, 25% indigestible material, mucus and bacteria • Color: produced by bile • Gas: produced by the metabolism of bacteria or from swallowing air • Movement of matter is very slow ~ 18-24 hours

32. Carbohydrate Digestion • Carbohydrate: nutrient; main source of energy in the body • Glucose: a simple sugar; the end product of carbohydrate digestion • Takes place in the mouth & small intestine

33. Protein Digestion • Protein: basic nutrient; used in anabolism (tissue building) • Amino Acid: the building blocks of proteins; the end product of protein digestion • Takes place in the stomach & small intestine

34. Fat Digestion • Fat: basic food type; used for energy • Fatty acids and glycerol: end products of fat digestion • Takes place in the small intestine • Enzymes: • Bile in duodenum: fat droplets into smaller fat droplets

35. Time to Digest • Carbohydrate-rich meal: moves through the stomach rapidly • Fat-rich meals: may take up to 6 hours to pass through the stomach

36. Digestion Mishaps • Heartburn: the damage to esophageal mucosa due to presence of stomach acids because of a weak cardio-esophageal sphincter • Gastric ulcer: when the mucus layer of the stomach is not strong enough to withstand gastric acids; burns a hole in stomach wall

37. Digestion Mishaps • Diarrhea: the decreased absorption of water and electrolytes in the small & large intestine leading to watery stool • Constipation: the increased absorption of water and electrolytes in the large intestine; leads to hard, impacted stool