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24-1 Lecture 22 Digestive System II. 24-2 Small Intestine Site of greatest amount of digestion and absorption Divisions –Duodenum (“twelve finger widths”)

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Presentation on theme: "24-1 Lecture 22 Digestive System II. 24-2 Small Intestine Site of greatest amount of digestion and absorption Divisions –Duodenum (“twelve finger widths”)"— Presentation transcript:

1 24-1 Lecture 22 Digestive System II

2 24-2 Small Intestine Site of greatest amount of digestion and absorption Divisions –Duodenum (“twelve finger widths”) –Jejunum (“empty”) –Ileum (“twisted”) Fig Duodenum Jejunum Ileocecal valve Ileum

3 24-3 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

4 24-4 Duodenum and Pancreas Duodenum 25cm in adult Accessory glands empty secretions into duodenum Fig

5 24-5 Histology of Small Intestine Circular folds, villi and microvilli increase surface area Epithelial cells produced by intestinal glands Fig

6 24-6 Liver 4 Lobes Ducts –Cystic duct joins with common hepatic duct to form common bile duct –Common bile duct joins pancreatic duct Fig Right lobe Inferior vena cava Left lobe Gallbladder (a) Anterior view Left lobe Hepatic portal vein Common hepatic duct Quadrate lobe Inferior vena cava Right lobe Cystic duct Gallbladder Caudate lobe Posterior Anterior (b) Posteroinferior view

7 24-7 Functions of the Liver Bile production –Salts emulsify fats, neutralizes stomach acid –Stored in gall bladder –Gallstones can form as precipitate of cholesterol Storage –Glycogen, fat, vitamins, copper and iron Nutrient interconversion Detoxification –Removal of ammonia and conversion to urea (eliminated by kidneys in urine) Phagocytosis –Removal of worn-out and dying red and white blood cells, some bacteria Synthesis –Blood proteins

8 24-8 Pancreas Anatomy –Endocrine Insulin –Exocrine Pancreatic juice –Digestive enzymes –Released in inactive form –Become active in duodenum –Digest protein, fats, carbohydrates, and nucleic acids

9 24-9 Review Question Digestion of proteins is started in the ______________ and completed in the ________________. (a)Oral cavity, stomach (b)Stomach, small intestine (c)Esophagus, small intestine (d)Oral cavity, small intestine (e)Esophagus, stomach

10 24-10 Large Intestine Extends from ileocecal valve to anus Consists of cecum, colon, rectum, anal canal Movements sluggish ( hours) Fig Transverse colon Ascending colon Descending colon Cecum Vermiform appendix Sigmoid colon Ileocecal valve Cecum Vermiform appendix Rectum Ileum Anal canal

11 24-11 Movement in Large Intestine Mass movements –Common after meals 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 (breathing in) and contraction of abdominal wall muscles Rectal valve Anal canal Veins Internal anal sphincter External anal sphincter Anus Rectum Fig

12 24-12 Points to Remember Stomach –Mixes food –Protein digestion –Limited absorption (aspirin) Small intestine –Receives secretions of liver and pancreas –Chemical and mechanical digestion –Transports undigested material Large intestine –Absorb water –Form, store and expel feces

13 24-13 Questions?


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