Phases of Gastric Secretion

1. Phases of Gastric Secretion

2. Stomach Histology • Rugae: Folds in stomach when empty • Gastric pits: Openings for gastric glands • Contain cells • Surface mucous: Mucus • Mucous neck: Mucus • Parietal: Hydrochloric acid and intrinsic factor • Chief: Pepsinogen • Endocrine: Regulatory hormones

5. Hydrochloric Acid Production

6. Movements in Stomach

8. Small Intestine • Site of greatest amount of digestion and absorption • Divisions • Duodenum • Jejunum • Ileum: Peyer’s patches or lymph nodules • Modifications • Circular folds or plicae circulares, villi, lacteal, microvilli • Cells of mucosa • Absorptive, goblet, granular, endocrine

9. Movement in small intestine: • Mixing: Segmental contraction that occurs in small intestine • Secretion: Lubricate, liquefy, digest • Digestion: Mechanical and chemical • Absorption: Movement from tract into circulation or lymph • Elimination: Waste products removed from body

10. Small Intestine Secretions • Mucus • Protects against digestive enzymes and stomach acids • Digestive enzymes • Disaccharidases: Break down disaccharides to monosaccharides • Peptidases: Hydrolyze peptide bonds • Nucleases: Break down nucleic acids • Duodenal glands • Stimulated by vagus nerve, secretin, chemical or tactile irritation of duodenal mucosa

11. Duodenum and Pancreas

13. Duodenum Anatomy and Histology

14. Liver • Lobes • Major: Left and right • Minor: Caudate and quadrate • Ducts • Common hepatic • Cystic • From gallbladder • Common bile • Joins pancreatic duct at hepatopancreatic ampulla

17. Blood and Bile Flow

18. Duct System

19. Gallbladder • Bile is stored and concentrated • Stimulated by cholecystokinin and vagal stimulation • Dumps into small intestine • Production of gallstones possible • Drastic dieting with rapid weight loss

20. Pancreas • Anatomy • Endocrine • Pancreatic islets produce insulin and glucagon • Exocrine • Acini produce digestive enzymes • Regions: Head, body, tail • Secretions • Pancreatic juice (exocrine) • Trypsin • Chymotrypsin • Carboxypeptidase • Pancreatic amylase • Pancreatic lipases • Enzymes that reduce DNA and ribonucleic acid

21. Bicarbonate Ion Production

22. Gastric hormones:

23. Liver Histology portal triad Figure 24.20a, b

24. 3. Architecture of the Hepatic Parenchyma The hepatic lobuleis the structural unit of the liver. Portal vein Bile duct Sinusoids Central vein Liver cells (Hepatocytes) Portal area Hepatic artery

25. Bile …each day around 600 ml of bile is produced… • Bile acid • Phospholipids • Cholesterol • Bilirubin • Waste products • Electrolytes • Mucin

26. Functions of the Liver • Bile production • Salts emulsify fats, contain pigments as bilirubin • Storage • Glycogen, fat, vitamins, copper and iron; huge blood reservoir of blood (storage); very high lymph flow • Nutrient interconversion – Metabolic functions (see next slide) • Detoxification • Hepatocytes remove ammonia and convert to urea; metabolizes drugs, hormones; has the Cytochrome P-450 enzyme system. • Phagocytosis – Cleans the blood • Kupffer cells phagocytize worn-out and dying red and white blood cells, some bacteria • Synthesis • Albumins, fibrinogen, globulins, heparin, clotting factors

27. Liver’s Role in Metabolism Carbohydrate Metabolism • Storage of large amounts of glycogen • Conversion of galactose and fructose to glucose • Gluconeogenesis • Formation of many chemical compounds from intermediate products of carbohydrate metabolism Fat Metabolism • Beta-oxidation of fatty acids to supply energy to for other functions in the body • Synthesis of cholesterol, phospholipids, and most lipoproteins (and their receptors) • Synthesis of fats from proteins and carbohydrates

28. Liver’s Role in Metabolism (cont’d) Protein Metabolism • Deamination of amino acids • Formation of urea for removal of ammonia from the body fluids • Formation of plasma proteins • Interconversion of the various amino acids and synthesis of other compounds from amino acids

29. Exocrine Pancreas – Enzymes • Trypsinogen • Chymotrysinogen • Carboxypeptidases • Pro-elastase • Phospholipase • pancreatic lipase • Pancreatic amylase

30. Bicarbonate Ion Production

37. Lipoproteins • Types • Chylomicrons • Enter lymph • VLDL • LDL • Transports cholesterol to cells • HDL • Transports cholesterol from cells to liver

39. Water and Ions: • Water • Can move in either direction across wall of small intestine depending on osmotic gradients • Ions • Sodium, potassium, calcium, magnesium, phosphate are actively transported

40. Large Intestine: • Extends from ileocecal junction to anus • Consists of cecum, colon, rectum, anal canal • Movements sluggish (18-24 hours)

41. Large Intestine • Cecum • Blind sac, vermiform appendix attached • Colon • Ascending, transverse, descending, sigmoid • Rectum • Straight muscular tube • Anal canal • Internal anal sphincter (smooth muscle) • External anal sphincter (skeletal muscle) • Hemorrhoids: Vein enlargement or inflammation

42. Secretions of Large Intestine • Mucus provides protection • Parasympathetic stimulation increases rate of goblet cell secretion • Pumps • Exchange of bicarbonate ions for chloride ions • Exchange of sodium ions for hydrogen ions • Bacterial actions produce gases called flatus

43. Histology of Large Intestine

44. Movement in Large Intestine • Mass movements • Common after meals • Local reflexes in enteric plexus • Gastrocolic: Initiated by stomach • Duodenocolic: Initiated by duodenum • Defecation reflex • Distension of the rectal wall by feces • Defecation • Usually accompanied by voluntary movements to expel feces through abdominal cavity pressure caused by inspiration

45. Reflexes in Colon and Rectum:

46. Digestion, Absorption, Transport • Digestion • Breakdown of food molecules for absorption into circulation • Mechanical: Breaks large food particles to small • Chemical: Breaking of covalent bonds by digestive enzymes • Absorption and transport • Molecules are moved out of digestive tract and into circulation for distribution throughout body

47. Effects of Aging • Death of myenteric plexus neurons • Atrophy of sphincter muscles Incontinence • Decrease in mucus layer, connective tissue, muscles and secretions • Increased susceptibility to infections and toxic agents • Ulcerations and cancers