Understanding Digestive System: Liver, Colon, Absorption

1. Chapter 24, part 4 The Digestive System

2. The liver • Performs metabolic and hematological regulation and produces bile • Histological organization • Lobules containing single-cell thick plates of hepatocytes • Lobules unite to form common hepatic duct • Duct meets cystic duct to form common bile duct

3. Figure 24.19 The Anatomy of the Liver Figure 24.19a

4. Figure 24.19 The Anatomy of the Liver Figure 24.19b, c

5. Liver lobule is the basic functional unit of the liver • Hepatocytes form irregular plates arranged in spoke-like fashion • Bile canaliculi carry bile to bile ductules • Bile ductules lead to portal areas

6. Figure 24.20 Liver Histology Figure 24.20a, b

7. The gallbladder • Hollow, pear-shaped organ • Stores, modifies and concentrates bile PLAY Animation: Accessory Organ

8. Figure 24.21 The Gallbladder Figure 24.21a, b

9. Coordination secretion and absorption • Neural and hormonal mechanisms coordinate glands • GI activity stimulated by parasympathetic innervation • Inhibited by sympathetic innervation • Enterogastric, gastroenteric and gastroileal reflexes coordinate stomach and intestines

10. Figure 24.22 The Activities of Major Digestive Tract Hormones Figure 24.22

11. SECTION 24-7The Large Intestine

12. Functions of the large intestine • Reabsorb water and compact material into feces • Absorb vitamins produced by bacteria • Store fecal matter prior to defecation

13. The four areas of the colon are: • Ascending • Transverse • Descending • Sigmoid

14. Figure 24.23 The Large Intestine Figure 24.23a

15. Figure 24.23 The Large Intestine Figure 24.23b, c

16. The rectum • Last portion of the digestive tract • Terminates at the anal canal • Internal and external anal sphincters

17. Histology of the large intestine • Absence of villi • Presence of goblet cells • Deep intestinal glands

18. Physiology of the large intestine • Reabsorption in the large intestine includes: • Water • Vitamins – K, biotin, and B5 • Organic wastes – urobilinogens and sterobilinogens • Bile salts • Toxins • Mass movements of material through colon and rectum • Defecation reflex triggered by distention of rectal walls

19. Figure 24.25 The Defecation Reflex Figure 24.25

20. SECTION 24-8Digestion and Absorption

21. Processing and absorption of nutrients • Disassembles organic food into smaller fragments • Hydrolyzes carbohydrates, proteins, lipids and nucleic acids for absorption

22. Carbohydrate digestion and absorption • Begins in the mouth • Salivary and pancreatic enzymes • Disaccharides and trisaccharides • Brush border enzymes • Monosaccharides • Absorption of monosaccharides occurs across the intestinal epithelia

23. Lipid digestion and absorption • Lipid digestion utilizes lingual and pancreatic lipases • Bile salts improve chemical digestion by emulsifying lipid drops • Lipid-bile salt complexes called micelles are formed • Micelles diffuse into intestinal epithelia which release lipids into the blood as chylomicrons

24. Protein digestion and absorption • Low pH destroys tertiary and quaternary structure • Enzymes used include pepsin, trypsin, chymotrypsin, and elastase • Liberated amino acids are absorbed

25. Absorption • Water • Nearly all that is ingested is reabsorbed via osmosis • Ions • Absorbed via diffusion, cotransport, and active transport • Vitamins • Water soluble vitamins are absorbed by diffusion • Fat soluble vitamins are absorbed as part of micelles • Vitamin B12 requires intrinsic factor

26. Figure 24.27 Digestive Secretion and Absorption of Water Figure 24.27

27. Figure 24.28 Ion and Vitamin Absorption by the Digestive Tract Figure 24.28

28. SECTION 24-9Aging and the Digestive System

29. Age related changes in the digestive system include: • Thinner, more fragile epithelium • Reduction in epithelial stem cells • Weaker peristaltic contractions • Effects of cumulative damage • Increased cancer rates

30. You should now be familiar with: • The organs of the digestive system and their major functions • The mechanisms that regulate digestion • The anatomy of the organs and accessory organs of the digestive system • The functions of the major structures and regions of the digestive system and the regulation of their activities

31. You should now be familiar with: • The significance of the large intestine in the absorption of nutrients • The events involved in the digestion of organic and inorganic nutrients • The effects of the aging process on the digestive system