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Lecture 22 Digestive System II.

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1 Lecture 22 Digestive System II

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

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

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

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

7 Functions of the Liver Bile production Storage
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 Pancreas Anatomy Endocrine Exocrine Insulin Pancreatic juice
Digestive enzymes Released in inactive form Become active in duodenum Digest protein, fats, carbohydrates, and nucleic acids

9 Review Question Digestion of proteins is started in the ______________ and completed in the ________________. Oral cavity, stomach Stomach, small intestine Esophagus, small intestine Oral cavity, small intestine Esophagus, stomach

10 Large Intestine Extends from ileocecal valve to anus
Transverse colon Extends from ileocecal valve to anus Consists of cecum, colon, rectum, anal canal Movements sluggish (18-24 hours) Descending colon Ascending colon Cecum Sigmoid colon Vermiform appendix Ileocecal valve Cecum Ileum Vermiform appendix Rectum Anal canal Fig

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 Rectum Anal canal Veins Internal anal sphincter Anus External anal sphincter Fig

12 Points to Remember Stomach Small intestine Large intestine 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 Questions?

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