Chapter 24, part 4 The Digestive System

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

Figure 24.19 The Anatomy of the Liver Figure 24.19a

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

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

Figure 24.20 Liver Histology Figure 24.20a, b

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

Figure 24.21 The Gallbladder Figure 24.21a, b

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

Figure 24.22 The Activities of Major Digestive Tract Hormones

SECTION 24-7 The Large Intestine

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

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

Figure 24.23 The Large Intestine Figure 24.23a

Figure 24.23 The Large Intestine Figure 24.23b, c

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

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

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

Figure 24.25 The Defecation Reflex

SECTION 24-8 Digestion and Absorption

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

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

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

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

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

Figure 24.27 Digestive Secretion and Absorption of Water

Figure 24.28 Ion and Vitamin Absorption by the Digestive Tract

SECTION 24-9 Aging and the Digestive System

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

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

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