1. DIGESTIVE SYSTEM Anatomy and Physiology of the Digestive Tract

2. DIGESTIVE ANATOMY Mouth and tongue Salivary Glands Pharynx Esophagus Stomach Liver Pancreas Small intestine Large intestine

3. LAYERS OF THE GI TRACT (1) SEROSA:- OUTER TOUGH CONNECTIVE TISSUE MEMBRANE FOR PROTECTION. (2) MUSCULARIS EXTERNA:- LONGITUDENAL AND CIRCULAR MUSCLE LAYERS FOR CONTRACTION (3) SUBMUCOSA:- LOOSE CONNECTIVE TISSUE, BLOOD VESSELS AND GLANDS.

4. LAYERS OF THE GI TRACT (4) MUCOSA:- MADE OF THREE LAYERS (A) MUSCULARIS MUCOSA (B) LAMINA PROPRIA (C) EPITHELIUM LINNING FUNCTION FOR DIGESTION AND ABSORPTION OF NUTRIENTS.

5. LAYERS OF THE GI TRACT Muscularis Mucosa Submucosa

6. FUNCTIONS OF THE GI TRACT INGESTION MECHANICAL DIGESTION CHEMICAL DIGESTION SECRETION ABSORPTION EXCRETION

7. DIGESTIVE ENZYMES Enzymes are protein catalysts Enzymes are not altered themselves Enzymes speed up reactions at body temperatures Digestive enzymes are called hydrolytic enzymes. Water is used to split food molecules

8. DIGESTIVE ENZYMES Enzymes are sensitive to such things as temperature and pH The names of enzymes usually end in “ase” For example, sucrase is the enzyme that catalyzes the hydrolysis of the sugar sucrose

9. DIGESTION IN THE MOUTH Mastication –Another name for chewing –Breaks-up and lubricates the food Swallowing is easier Increases surface area of food so enzymes can work more efficiently

10. DIGESTION IN THE MOUTH Salivary amylase, secreted by salivary glands, digests starch into smaller molecules, the smallest being the disaccharides. StarchDisaccharides amylase

11. SWALLOWING Tongue pushes bolus of food from oral cavity into oropharynx

12. SWALLOWING Soft palate closes nasopharynx and epiglottis closes glottis

13. SWALLOWING ESOPHAGEAL PHASE Upper esophageal sphincter open Peristalsis propels bolus down esophagus toward stomach

14. SWALLOWING Cardiac (lower esophageal) sphincter opens and bolus enters stomach

15. STOMACH HISTOLOGY Gastric Pit----------------- Gastric Gland------------ Rugae---------------------

16. GASTRIC GLANDS Gastric glands –Mucous neck cells secrete protective mucus –Parietal cells secrete hydrochloric acid and intrinsic factor –Chief cells secrete pepsinogen and gastric lipase –G cells secrete hormone gastrin which stimulates gastric secretions Mucous Neck cells----------- Parietal cell------------------- Chief cell---------------------- G cell----------------------------

17. FUNCTIONS OF THE STOMACH (1) Storage:- can eat lots of food at one sitting (2) Mechanical Digestion –Mixing waves every 15-20 seconds Reduce food to liquid acid chyme Force small amounts of chyme from stomach into the small intestine (3) Chemical digestion –Protein digestion begins –Inactive enzyme pepsinogen secreted by chief cells of gastric glands

18. CHEMICAL DIGESTION Pepsinogen Converted to active enzyme pepsin in stomach lumen (cavity) by hydrochloric acid (HCl) Pepsin digests proteins to smaller polypeptides Pepsinogen HCl Pepsin ProteinPolypeptides

19. FUNCTIONS OF THE STOMACH (4) Limited absorption –Aspirin and some other drugs –Alcohol –Some water –Electrolytes

20. SMALL INTESTINE HISTOLOGY Lined with about 4.5 million villi (villus) –Small finger like extensions –Covered with a simple columnar mucous membrane –Blood capillaries inside for absorbing most substances –Single lymph capillary called a lacteal for absorbing most fat

21. THE VILLUS Blood Capillaries------------- Simple Columnar Cells------- Lacteal-------------------------- ---------Absorptive Cell ---------Goblet Cell ---------Endocrine Cell -----------Paneth Cell of intestinal crypt

22. SMALL INTESTINE FUNCTIONS (1) Mechanical digestion –Peristalsis propels chyme along intestine –Segmentation move chymes back and forth to mix it thoroughly (2) Chemical digestion –Enzymes from pancreas and small intestine complete digestion of protein, starch, disaccharide sugars and fat –Gallbladder empties bile into small intestine to aid in fat digestion (3) Absorption of most substances

23. THE PANCREAS Head, neck,body and tail Head into duodenum Tail to spleen Pancreatic duct joins bile duct and connect to duodenum

24. HISTOLOGY OF PANCREAS Acini are exocrine cells that secrete digestive enzymes into ducts Duct cells secrete bicarbonate to buffer the acid chyme from stomach and raise its pH from 2-3 to 7-8

25. SECRETION OF PANCREATIC JUICE Enzymes are secreted by Acinar cells Bicarbonate solution is secreted by Ductal cells About 1 liter of pancreatic juice is secreted by the pancreas per day Bicarbonate solution neutralize the acidity Enzymes digest proteins, starch and fat

26. DIGESTION BY PANCREATIC ENZYMES Proteins Digestion –Four proteolytic enzymes secreted as inactive proenzymes –Proenzymes sequentially activated in duodenum –These enzymes digest proteins & polypeptides to smaller peptides.

27. DIGESTION BY PANCREATIC ENZYMES Starch digestion –Remaining starch is digested in intestine by pancreatic amylase –Digestion same as in the mouth STARCH > AMYLASE > DISACCHARIDES

28. DIGESTION BY PANCREATIC ENZYMES Fats digestion –Triglycerides (fat molecules made of glycerol and three fatty acids) digested in small intestine by pancreatic lipase –Digestion of each triglyceride yields a monoglyceride molecule and two fatty acid molecules Monoglyceride lipase Triglyceride+Two fatty acids

29. ROLE OF BILE Bile from the gallbladder is required for lipase to digest fat more efficiently. Bile flows from gallbladder down the bile duct into duodenum to mix with and emulsify the fat. Emulsification is breaking fat drops into very small droplets

30. THE LIVER – Anterior View

31. THE LIVER – Posterior View

32. LIVER HISTOLOGY Lobes contain microscopic lobules Lobules consist of rows (plates) of liver cells (hepatocytes) and rich blood supply Blood supplied by branches of the hepatic artery and portal vein at six corners of lobule

33. LIVER HISTOLOGY Blood flows toward the center of each lobule through liver capillaries (sinusoids) Rows of liver cells surround the capillaries Blood flows from the capillaries into the central vein in the center of the lobule Liver macrophages called Kupffer cells are in the capillaries

34. LIVER HISTOLOGY central vein----------------------------------------- Sinusoid---------------------------- (liver capillary) portal vein---------------------- hepatic artery------------------------- Kupffer cell------------------------ Hepatocyte------------------- bile duct------------------

35. THE BILIARY SYSTEM Liver secretes bile Bile flows from liver through hepatic ducts into the ballbladder Gallbladder stores and concentrates bile Common hepatic duct and cystic duct from GB unite to form common bile duct Common bile duct unites with pancreatic duct Bile and pancreatic juices enter the duodenum

36. THE BILIARY SYSTEM One-half to one liter of bile secreted by the liver each day Functions of bile –Emulsification of fat in small intestine –Aids in fat absorption –Excretion of bilirubin and cholesterol

37. FUNCTIONS OF THE LIVER (1) Carbohydrate, lipid and amino acid metabolism (2) Removal of waste products (3) Storage of glycogen, vitamins and iron (4) Phagocytosis by Kupffer cells (5) Detoxification (6) Bile secretion (7) Plasma protein synthesis

38. DIGESTION BY INTESTINAL ENZYMES Called brush-border enzymes –Located in microvilli of intestinal absorptive cells Peptidases digest peptides to amino acids Intestinal lipase digest fats to glycerol & fatty acids

39. DIGESTION BY INTESTINAL ENZYMES Disaccharidases digest disaccharides to monosaccharides SucroseGlucose + Fructose sucrase Maltose maltase Glucose + Glucose Lactose lactase Glucose + Galactose

40. ABSORPTION IN THE SMALL INTESTINE Absorption is the transfer (uptake) of substances into absorptive cells then into blood or lymph Villi and microvilli of absorptive cells provide a very large surface area for absorption Most digested foods, water, electrolytes, vitamins are absorbed in the small intestine

41. ABSORPTION IN THE SMALL INTESTINE Absorption into the blood –Monosaccharides –Amino acids –Water –Electrolytes –Water soluble vitamins

42. ABSORPTION IN THE SMALL INTESTINE Absorption into the lacteals (lymph capillaries in villi) –Fat soluble vitamins –Fats (triglycerides) Bile aids in absorption of fat digestion products (fatty acids and monoglycerides) Fat digestion products converted back to triglycerides in absorptive cells

43. ABSORPTION IN THE SMALL INTESTINE Triglycerides and other lipids combine with protein to form small water soluble particles called chylomicrons Chylomicrons absorbed into lymph of lacteals

44. INTESTINAL ABSORPTION

45. LARGE INTESTINE HISTOLOGY Simple columnar mucosa Deep crypts with intestinal glands Glands secrete lots of mucus No villi

46. FUNCTIONS OF THE LARGE INTESTINE (1) Feces formation by bacterial action (2) Limited digestion of undigested food by bacteria (3) Formation of vitamin K and some B vitamins by bacteria (4) Absorption of some water, electrolytes, vitamins and bile salts

47. CLINICAL TERMS Gingivitis:- Inflammation of the gums Periodontal disease:- Inflammations of the teeth, ligaments and alveolar bones Stomatitis:- Inflammation of the mouth Esophagitis:- Inflammation of esophagus

48. CLINICAL TERMS Gastritis:- Inflammation of the stomach Enteritis:- Inflammation of small intestine Diverticulitis:- inflammation of the colon Hepatitis:- inflammation of the liver Pancreatitis:- Inflammation of the pancreas