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The Digestive System

The Digestive System. Functions of Digestive System. food. blood. Absorbable nutrients. lumen. wall. wall. Intestines. digestion. food. blood. Absorbable nutrients. lumen. wall. wall. Intestines. digestion. food. blood. Absorbable nutrients. absorption. Forms of Nutrients.

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The Digestive System

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  1. The Digestive System

  2. Functions of Digestive System food blood Absorbable nutrients lumen wall wall Intestines

  3. digestion food blood Absorbable nutrients lumen wall wall Intestines

  4. digestion food blood Absorbable nutrients absorption

  5. Forms of Nutrients In FoodAbsorbable by Intestine ProteinAmino acids CarbohydratesMonosaccharides (glucose) FatFatty acids, glycerol DNA, RNABases + monosaccharides Vit B12B12+intrinsic factor Other vitamins Original form Cholesterol Original form Electrolytes Original form Water Original form

  6. digestion food blood Amino acids Glucose Fatty acids, Glycerol Bases + monosaccharides vitamins Cholesterol Electrolytes, Water absorption

  7. The Organs of the Digestive System The Mouth The Salivary Glands The Esophagus The Stomach The Liver The Gallbladder The Pancreas The Small intestines The Large intestines

  8. The Mouth has the following functions : 1) breaking food 2) sense of taste 3) swallowing 4) speech

  9. Saliva and the Salivary Glands • moisten food and the mouth • clean the teeth, inhibit bacterial growth, • dissolve molecules so they can stimulate taste buds • digest a small amount of starch and fat

  10. Esophagus

  11. Esophagus

  12. The Stomach

  13. The Stomach • Functions • food storage • host defense • minor role in digestion and • absorption of nutrients • - The above functions are performed via gastric secretion and motility Gastric pits

  14. mucous cells: produce mucus The bottom part of the pits is the gastric gland. parietal cells: produce HCland intrinsic factor G cells: produce hormones that regulate digestion chief cells: produce pepsinogen

  15. The gastric glands produce 2-3 L of gastric juice daily, containing: • pepsinogen • HCl • intrinsic factor

  16. Pepsinogen - is the inactive precursor of the active enzyme pepsin. - activated by HCl or pepsin. Pepsinogen Pepsin: chop proteins into small fragments

  17. HCl Hydrochloric Acid (HCl ) - reduces pH of gastric juice to as low as pH 0.8.

  18. Functions of HCl: • activates pepsinogen into pepsin. • (2) breaks up connective tissues and plant cell walls. • (3) converts ferric ions to ferrous ions. • (4) destroys ingested pathogens. HCl

  19. Self protection of the stomach from HCl and pepsin by HCl • a highly alkaline mucous coat. • rapid replacement of epithelial cells (3-6 d) • tight junctions between epithelial cells

  20. Intrinsic Factor - is essential to the absorption of vitamin B12 - is the only indispensable function of the stomach. Intrinsic Factor

  21. Gastrin secreted by G cells in gastric gland not into gastric juice but blood • is a hormone • stimulates • the secretion of HCl and pepsinogen • motility of the large intestine

  22. Gastric Motility • relax during swallowing • stretch further when food enters the stomach (stress-relaxation response) - Next, pacemaker cells in the greater curvature initiate peristaltic contractions. - Each peristaltic wave pushs ~ 3 mL of chyme into the duodenum.

  23. Regulation of Gastric Function • Gastric secretion and motility is divided into three stages: • 1) Cephalic • 2) Gastric • 3) Intestinal phases

  24. 1) The Cephalic Phase The cephalic phase is stimulated by the sight, smell, taste, or mere thought of food.

  25. 2) The Gastric Phase - is stimulated by food in the stomach - accounts for two-thirds of gastric secretion.

  26. 3) The Intestinal Phase After entering small intestines,chyme inhibit gastric secretion and mobility via: • the enterogastric reflex. • local hormones • Secretin • Cholecystokinin • gastric inhibitory peptide

  27. The small intestine receives not only chyme from the stomach but also secretions from the liver and pancreas.

  28. The Liver has tremendous variety of functions, including the secretion of bile for digestive purposes.

  29. Hepatocytes secret bile into the bile canaliculi and bile ductules. bile ductule

  30. common hepatic duct Bile ductules hepatic ducts  cystic duct common hepatic duct common bile duct gallbladder hepatopancreatic sphincter pancreas duodenum

  31. When no chyme is in the small intestine, the hepatopancreatic sphincter is closed. Bile flows into gallbladder. cystic duct common hepatic duct common bile duct gallbladder hepatopancreatic sphincter pancreas duodenum

  32. Function of Gallbladder - absorbs water and stores the bile for later use. gallbladder hepatopancreatic sphincter duodenum

  33. Bile • - is constantly produced by the liver (500-1,000 mL of bile per day). • - is a yellow-green fluid containing : • minerals • bile pigments • bile acids • phospholipids • cholesterol • neutral fats facilitate fat digestion and absorption

  34. Recycle ofBile acids and Phospholipids - reabsorbed in the ileum and returned to the liver via enterohepatic circulation. Bile acids phospholipids

  35. The Pancreas

  36. The Pancreas • Exocrine: • - secretes pancreatic juice into the lumen of the pancreatic duct • Endocrine: • secretes insulin, glucagon, somatostatin into the blood.

  37. Exocrine secretes 1,200-1,500 mL of pancreatic juice per day into the main pancreatic duct. It empties into duodenum when hepato-pancreatic sphincter opens.

  38. Pancreatic juice is an alkaline mixture containing: • 1) sodium bicarbonate: neutralize HCl 2) inactive digestive enzymes and zymogens which are activated after secreted into duodenum. The activated enzymes digest carbohydrates, lipids, RNA, DNA, and proteins.

  39. Regulation of Bile and Pancreatic Secretion • secreted in response to similar stimuli. • Cephalic and Gastric phases • The vagus nerves stimulate pancreatic secretion.

  40. The Intestinal Phase - Chyme with acid and fat, stimulate the duodenal mucosa to secrete cholecystokinin (CCK). • 1) relaxation of the hepatopancreatic sphincter, • 2) the contraction of the gallbladder • 3) secretion of pancreatic juice and enzymes.

  41. The Intestinal Phase - Acidic chyme also stimulates the duodenum to release secretin. secretion of bicarbonate by both the hepatic and pancreatic ducts

  42. The Small Intestine

  43. Overview - Nearly all chemical digestion and nutrient absorption occur in the small intestines.

  44. 1) The duodenum - ~ 25 cm 2) The jejunum - comprises the next 2.5 m. 3) The ileum - forms the last 3.6 m.

  45. - The surface area inside the small intestine is greatly increased by circular folds, villi, and microvilli. villi

  46. Microvilli (brush border) brush border enzymes

  47. brush border enzymes • activates zymogens • complete digestion of carbohydrates and proteins

  48. Secretion by the small intestines - 1-2 L of intestinal juice per day. - The duodenum endocrine cells secret cholecystokinin (CCK) and secretin. (Both are hormones.)

  49. Chemical Digestion and Absorption of Nutrients

  50. Chemical Digestion and Absorption of Nutrients Carbohydrates Proteins Lipids Nucleic Acids Vitamins Minerals Water

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