Digestive System Includes:

1. Digestive System Includes: • GI tract • (gastrointestinal (digestive) tract • alimentary canal) • Accessory organs: • teeth, • salivary glands, • liver, • gallbladder, • pancreas

2. Digestion Involves Many Processes: • INGESTION- process of taking food and liquid into mouth (eating) • SECRETION (water, acid, buffers, enzymes) -7L/day • DIGESTION (chemical, mechanical) • Extracellularprocess, occurs within the gut

4. Digestion Involves Many Processes: • MOTILITY(peristalsis) Mixing and propulsion – alternating contraction and relaxation of smooth muscle in walls of GI tract mix food and secretions and move them toward the anus (motility) • Absorption: the passage of digested nutrients from the gut lumen into the blood or lymph,which distributes them through the body. • Elimination: the expulsion of indigestible residues from the body. (Defecation)

7. salivary glands

8. Saliva • Moistens and lubricates food • Components: • water(99%) • mucus: • salivary amylase • lysozyme • bicarbonate • Once food has been chewed, it is called a bolus

9. UNIT B Chapter 9: Digestive System Section 9.1 TO PREVIOUS SLIDE

10. UNIT B Chapter 9: Digestive System Section 9.1 The pharynx is a passageway that receives air from the nasal cavities and food from the mouth. Swallowing (a reflex action) occurs in the pharynx. The soft palate moves back to close off the nasopharynx The trachea moves up under the epiglottis to cover the glottis (the opening to the larynx (voice box)) During swallowing, food enters the esophagus because the air passages are blocked The Pharynx TO PREVIOUS SLIDE

11. UNIT B Chapter 9: Digestive System Section 9.1 The esophagus is a long muscular tube that moves food from the mouth to the stomach by peristalsis. Functions transport of food to the stomach secrete mucus (lubricates food and allows easy passage) NO digestive or absorptive function The Esophagus TO PREVIOUS SLIDE

12. Peristalsis Peristalsis (rhythmic muscular contractions) pushes food along the esophagus and through the digestive tract to the stomach.

13. UNIT B Chapter 9: Digestive System Section 9.1 The stomach is an organ that receives food from the esophagus, mechanically and chemically digests food, and moves food into the small intestine. The Stomach TO PREVIOUS SLIDE

14. Stomach Structure • Four regions: • Cardia • Fundus • Body • Pyloric part

15. Structure of Stomach • Three musclelayers: • Circular, • Longitudinal, • Oblique • Rugae – folds • 2 sphincters: • lower esophageal sphincter  prevents esophageal reflux • pyloric sphincter  regulates movement of stomach contents into the intestines

16. 4 Main Functions of Stomach • 1. Storage of a meal

17. 4 Main Functions of Stomach • 2. Mechanical Digestion

18. 4 Main Functions of Stomach • 3. Chemical Digestion

19. 4 Main Functions of Stomach • 4. Protection against Germs

20. What about Absorption? • Absorptionin the stomach is limited because: • thick layer of mucus • epithelial cells lack specialized transport mechanisms • most nutrients are not fully digested

21. What can be absorbed? Water, someions, some glucose, amino acids, lipid soluble substances Drugs Alcohol Some lipid soluble; diffuses through mucous membrane and cell membranes • Most Food is not absorbed here

22. UNIT B Chapter 9: Digestive System Section 9.1 When food leaves the stomach, it is a thick, soupy liquid called chyme. Chyme enters the small intestine by way of the pyloric sphincter. TO PREVIOUS SLIDE

24. Gastric Secretions • pepsinogen-an inactive enzyme that is converted to pepsin once released into the stomach(breaks down proteins) by chief cells • hydrochloric acid (HCl)- converts pepsinogen to pepsin; kills microorganisms. Secreted by parietal cells. • intrinsic factor- required for the absorption of vitamin B12 for RBC production. (parietal cells) • mucus- protects the stomach wall from gastric acid • gastrin - hormone that stimulates: • (1) HCl and pepsinogen release, • (2) gastric motility, (increase stomach movements) • (3) relaxes the pyloric sphincter

26. Peptic Ulcer • open sore • usually found in the • lining of the stomach, esophagus, • or upper small intestine. • gastric ulcers occur in stomach, • duodenal ulcers in duodenum.

27. UNIT B Chapter 9: Digestive System Section 9.1 The small intestine receives chyme from the stomach and completes the digestion of food. Macromolecules are broken down into nutrients, which are absorbed in the small intestine and pass into the blood. The Small Intestine TO PREVIOUS SLIDE

28. Secretions into duodenum

29. Secretions into the duodenum • Bile from liver & gall bladder • Pancreatic juice from pancreas • Digestive enzymes that finish the digestion of protein and starch (from interstitial glands within duodenum itself) • Mucus from goblet cells • Hormones from endocrine cells --> regulate stomach emptying, pancreatic secretions, gallbladder contraction, satiety, etc.

30. Small Intestine Enzymes • MALTASE digest maltose to glucose • SUCRASE digest sucrose to glucose and fructose. • LACTASE digest lactose to glucose and galactose. • LIPASE digest fats to fatty acids. • PEPTIDASE digest small peptides to single amino acids.

31. Enterogastric Reflex inhibits gastric motility and the secretion of gastric acid • Peristalsis - the longitudinal muscles within the small intestine wall contract, and then the circular muscles contract, pushing the food down the tract. • Segmentation –localized contraction of circular smooth muscles that constrict the intestine into segments mixing chymeand increasing contact with intestinal wall

32. Key Functions of Small Intestine • mechanical digestion (segmentation) • completion of chemicaldigestion, requires • enzymes from the pancreas and intestinal epithelial cells (complete nutrient digestion) • bile (digestion of fats) • alkaline pH (for enzyme function) • 90% of nutrient absorption

33. absorption takes place across the wall of each villus

34. UNIT B Chapter 9: Digestive System Section 9.1 Structure The wall of the small intestine contains plicae (circular folds) and villi (finger-like projections), which increase the surface area to improve the absorption of nutrients. Microvilli increase the surface area of the villus for the absorption of nutrients Each villus contains blood capillaries and a small lymphatic capillary called a lacteal Nutrients are absorbed into the blood capillaries and the lacteals, which carry them to body cells TO PREVIOUS SLIDE

35. CELIAC DISEASE • an inherited, autoimmune disease • antibodies attack the intestinal lining following the consumption of gluten (protein in wheat, rye and barley). • inflammation leads to the atrophy (flattening) of villi • impaired absorption  weight loss, malnutrition, anemia, fatty stools, fatigue

36. Lactose Intolerance • results from a deficiency in lactase • unabsorbed lactose provides fuel for bacteria in the colon gas production

38. Gastrointestinal Hormones • Gastrin • –Origin: Stomach • –Stimulus: Food in stomach • –Function: stimulate gastric glands secretion. • –Stimulates HCl & pepsinogen secretion, increases stomach motility

39. Gastrointestinal Hormones • Secretin • Origin: Duodenum • Stimulus: Acid chyme from stomach • Function: stimulate pancreatic juice secretion.

40. Gastrointestinal Hormones • Cholecystokinin (CCK) • Origin: Duodenum • Stimulus: Fat & protein in duodenum • Function: stimulate pancreatic secretion & gallbladder contraction.

41. Gastrointestinal Hormones • Gastric Inhibitory Protein (GIP) • –Origin: Duodenum • –Stimulus: Fats and bile • –Function: Inhibit stomach motility and secretion of acid and enzymes

42. UNIT B Chapter 9: Digestive System Section 9.1 The large intestine absorbs water, salts, and some vitamins. It also stores indigestible material until it is eliminated as feces. The Large Intestine TO PREVIOUS SLIDE

43. UNIT B Chapter 9: Digestive System Section 9.1 Structure and Function of the Large Intestine Colon: includes the ascending, transverse, descending, and sigmoid colon Rectum: the last part of the large intestine; opens at the anus Anus: rectum opening; site of defecation (expulsion of feces) TO PREVIOUS SLIDE

44. Fig. 12.8

45. Colon

46. Function of Large Intestine • Absorption of water • Bacteria produce vitamin K, B vitamins. • Secretion of mucus (lubrication of feces) • Contractions move feces along large intestine and rectum, to be expelled out of the anal canal • No digestion occurs in the large intestine.