Digestive System

1. Digestive System Honors Anatomy & Physiology

2. Unit 6A Learning Objectives 6.1 Name & identify the organs of the alimentary canal and accessory organs of digestive system, including wall of alimentary canal and the peritoneum 6.2 Identify overall function of digestive system and describe how each organ assists this function 6.3 Describe the 6 digestive processes required for the digestive system to function properly 6.4 Describe the composition and function of digestive secretions: saliva, pancreatic juices, bile, pepsin, HCl 6.5 Explain the anatomy of villi and their role in absorption of nutrients 6.6 Describe the mechanisms of swallowing, vomiting and defecation 6.7 Describe what happens to foodstuffs as they move along the GI tract 6.8 Differentiate between how proteins, fats and carbohydrates are digested-where and how 6.9 Identify some common ailments of the digestive system

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

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

5. 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

6. 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

7. 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

8. 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

9. http://www.nvcc.edu/home/lmiller/atlas/Digestive%20System/mesentary2.gifhttp://www.nvcc.edu/home/lmiller/atlas/Digestive%20System/mesentary2.gif

10. Wall Structure of Alimentary Canal • 4 layers • Mucosa/mucus membrane • Submucosa • Muscularis • Serosa http://www.lab.anhb.uwa.edu.au/mb140/CorePages/Oral/Images/gitplan.gif

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

12. 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

13. Wall Structure of Alimentary Canal 3. Muscularis: smooth muscular layer • Induces a propelling action called peristalsis • Has 2 parts: • Inner layer runs longitudinally • Outer layer (constrictor layer) runs circularly

14. Wall Structure of Alimentary Canal 4. Serosa - Visceral peritoneum -Outermost covering of alimentary canal

15. Alimentary Canal: Mouth • Function: receives food, 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 http://meltingmama.typepad.com/photos/uncategorized/2008/01/03/mouth_uvula.gif

16. Swallowing • Aka deglutition: occurs in 2 phases • Requires coordination from tongue, soft palate, pharynx and esophagus • 1. Buccal phase: food mixed with saliva to form bolus---forced into pharynx by tongue • 2. Pharyngeal-esophageal phase: involuntary, controlled by vagus nerve • Tongue blocks mouth, uvula of soft palate blocks nasal passage, larynx closed by epiglottis so food forced down esophagus

17. 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

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

19. 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

20. Esophagus continued - Mucosa: made of stratified squamous epithelium to resist abrasion - Cardio-esophageal sphincter: found at distal end; acts as a valve to prevent stomach contents from entering esophagus Sphincter: a circular muscle; acts as valve between organs

21. Vomiting • Aka emesis • Controlled by emetic center in brain (medulla) • Reverse peristalsis occurring in stomach or small intestine along with contraction of abdominal wall and diaphragm (increases internal pressure) • Causes: irritation of stomach (toxin); disturbance of equilibrium in inner ear

22. 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

23. Stomach continued • Divided into 4 regions: 1. cardia: receives bolus from-esophagus 2. fundus: expanded region, temporarily holding food

24. Stomach continued 3. body: main part of stomach - greater curvature: convex lateral margin -lesser curvature: concave medial margin 4. pyloris: inferior region with thickened walls -pyloric sphincter: valve that controls movement of food from stomach into small intestine

25. 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

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

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

28. 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 allows chyme to pass

29. 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 • Enzymes: • salivary amylase: starch to double sugars • pancreatic enzymes, intestinal enzymes (maltase, sucrase, lactase): double sugars to simple sugars

30. 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 • Enzymes: • Pepsin in gastric juices • Trypsin in pancreatic juice • Peptidases in intestinal juice

31. Fat Digestion • Basic food type; used for energy and insulation • 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 • Pancreatic lipase: small fat molecules into fatty acids and glycerol

32. 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

33. 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

34. 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

35. 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

36. 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

37. http://www.biog1105-1106.org/demos/105/unit6/media/villus.structure.jpghttp://www.biog1105-1106.org/demos/105/unit6/media/villus.structure.jpg

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

39. 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

40. 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

41. 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

42. 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

43. Mass Movement & Defecation • Food residue moves through large intestine via peristalsis and mass movement • Mass movements: slow moving powerful contractile waves over colon • Occurs 3-4X per day (oftentimes just after eating) • Defecation Reflex: feces stretching out rectum walls which contract while sphincters relax • Communication between rectum and brain to decide if “now is the time”

44. 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

45. 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