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Chapter 24, part 4 The Digestive System
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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
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Figure 24.19 The Anatomy of the Liver
Figure 24.19a
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Figure 24.19 The Anatomy of the Liver
Figure 24.19b, c
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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
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Figure 24.20 Liver Histology
Figure 24.20a, b
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The gallbladder Hollow, pear-shaped organ
Stores, modifies and concentrates bile PLAY Animation: Accessory Organ
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Figure 24.21 The Gallbladder
Figure 24.21a, b
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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
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Figure 24.22 The Activities of Major Digestive Tract Hormones
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SECTION 24-7 The Large Intestine
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Functions of the large intestine
Reabsorb water and compact material into feces Absorb vitamins produced by bacteria Store fecal matter prior to defecation
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The four areas of the colon are:
Ascending Transverse Descending Sigmoid
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Figure 24.23 The Large Intestine
Figure 24.23a
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Figure 24.23 The Large Intestine
Figure 24.23b, c
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The rectum Last portion of the digestive tract
Terminates at the anal canal Internal and external anal sphincters
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Histology of the large intestine
Absence of villi Presence of goblet cells Deep intestinal glands
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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
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Figure 24.25 The Defecation Reflex
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SECTION 24-8 Digestion and Absorption
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Processing and absorption of nutrients
Disassembles organic food into smaller fragments Hydrolyzes carbohydrates, proteins, lipids and nucleic acids for absorption
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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
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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
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Protein digestion and absorption
Low pH destroys tertiary and quaternary structure Enzymes used include pepsin, trypsin, chymotrypsin, and elastase Liberated amino acids are absorbed
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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
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Figure 24.27 Digestive Secretion and Absorption of Water
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Figure 24.28 Ion and Vitamin Absorption by the Digestive Tract
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SECTION 24-9 Aging and the Digestive System
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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
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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
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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
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