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24-2
Small Intestine
• Site of greatest amount of digestion and absorption
• Divisions – Duodenum (“twelve finger widths”)– Jejunum (“empty”)– Ileum (“twisted”)
Fig. 26.14
Duodenum
Jejunum
Ileocecal valve
Ileum
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
24-4
Duodenum and Pancreas
Duodenum• 25cm in adult• Accessory glands empty secretions into duodenum
Fig. 26.20
24-5
Histology of Small Intestine
• Circular folds, villi and microvilli increase surface area• Epithelial cells produced by intestinal glands
Fig. 26.15
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. 26.18
Right lobe
Inferior vena cava
Left lobe
Gallbladder(a) Anterior view
Left lobe
Hepaticportal vein
Commonhepatic duct
Quadrate lobe
Inferior vena cava
Right lobe
Cystic duct
Gallbladder
Caudate lobe
Posterior
Anterior(b) Posteroinferior view
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
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
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
24-10
Large Intestine
• Extends from ileocecal valve to anus
• Consists of cecum, colon, rectum, anal canal
• Movements sluggish (18-24 hours)
Fig. 26.16
Transverse colon
Ascending colon
Descending colon
Cecum
Vermiformappendix
Sigmoid colon
Ileocecal valve
CecumVermiform appendix
Rectum
Ileum
Anal canal
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. 26.16
24-12
Points to RememberPoints 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
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