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This 10 page Class Notes was uploaded by Jess Graff on Monday May 2, 2016. The Class Notes belongs to BMS 508 at University of New Hampshire taught by Mary Katherine Lockwood, PhD in Spring 2016. Since its upload, it has received 11 views. For similar materials see Human Anatomy and Physiology II in Biological Sciences at University of New Hampshire.
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Date Created: 05/02/16
BMS 508.03 4/8/2016 Chapter 24 (cont) Digestion & Metabolism (cont) The Liver (cont) • Hepatocytes • Many Kupffer cells (stellate reticuloendothelial cells) are located in sinusoidal lining • As blood flows through sinusoids: • Hepatocytes absorb solutes from plasma and secrete materials such as plasma proteins • The Bile Duct System • Liver secretes bile fluid • Into a network of narrow channels (bile canaliculi) • Between opposing membranes of adjacent liver cells • Right and Left Hepatic Ducts • Collect bile from all bile ducts of liver lobes • Unite to form common hepatic duct that leaves the liver • Bile Flow • From common hepatic duct to either: • The common bile duct, which empties into duodenal ampulla • The cystic duct, which leads to gallbladder • The Common Bile Duct • Is formed by union of: • Cystic duct • Common hepatic duct • Passes within the lesser omentum toward stomach • Penetrates wall of duodenum • Meets pancreatic duct at duodenal ampulla • The Physiology of the Liver • Metabolic regulation • Hematological regulation • Bile production • Metabolic Regulation • The liver regulates: • Composition of circulating blood • Nutrient metabolism • Waste product removal • Nutrient storage • Drug inactivation • Composition of Circulating Blood • All blood leaving absorptive surfaces of digestive tract • Enters hepatic portal system • Flows into the liver • Liver cells extract nutrients or toxins from blood • Before they reach systemic circulation through hepatic veins • Liver removes and stores excess nutrients • Corrects nutrient deficiencies by mobilizing stored reserves or performing synthetic activities • Metabolic Activities of the Liver • Carbohydrate metabolism • Lipid metabolism • Amino acid metabolism • Waste product removal • Vitamin storage • Mineral storage • Drug inactivation • Hematological Regulation • Largest blood reservoir in the body • Receives 25% of cardiac output • Functions of Hematological Regulation • Phagocytosis and antigen presentation • Synthesis of plasma proteins • Removal of circulating hormones • Removal of antibodies • Removal or storage of toxins • Synthesis and secretion of bile • The Functions of Bile • Dietary lipids are not water soluble • Mechanical processing in stomach creates large drops containing lipids • Pancreatic lipase is not lipid soluble • Interacts only at surface of lipid droplet • Bile salts break droplets apart (emulsification) • Increases surface area exposed to enzymatic attack • Creates tiny emulsion droplets coated with bile salts The Gallbladder • The Gallbladder • Is a hollow, pear-shaped, muscular sac • Stores and concentrates bile prior to excretion into small intestine • Is located in the fossa on the posterior surface of the liver’s right lobe • Regions of the Gallbladder • Fundus • Body • Neck • The Cystic Duct • Extends from gallbladder • Union with common hepatic duct forms common bile duct • Physiology of the Gallbladder • Stores bile • Releases bile into duodenum, but only under stimulation of intestinal hormone cholecystokinin (CCK) • CCK • Hepatopancreatic sphincter remains closed • Bile exiting liver in common hepatic duct cannot flow through common bile duct into duodenum • Bile enters cystic duct and is stored in gallbladder • Full gallbladder contains 40–70 mL bile • Bile composition gradually changes in gallbladder • Water is absorbed • Bile salts and solutes become concentrated Coordination of Secretion and Absorption • Neural and Hormonal Mechanisms • Coordinate activities of digestive glands • Regulatory mechanisms center around duodenum • Where acids are neutralized and enzymes added • Neural Mechanisms of the CNS • Prepare digestive tract for activity (parasympathetic innervation) • Inhibit gastrointestinal activity (sympathetic innervation) • Coordinate movement of materials along digestive tract (the enterogastric, gastroenteric, and gastroileal reflexes) • Motor neuron synapses in digestive tract release neurotransmitters • Intestinal Hormones • Intestinal tract secretes peptide hormones with multiple effects • In several regions of digestive tract • In accessory glandular organs • Hormones of Duodenal Enteroendocrine Cells • Coordinate digestive functions • Gastrin • Secretin • Gastric inhibitory peptide (GIP) • Cholecystokinin (CCK) • Vasoactive intestinal peptide (VIP) • Enterocrinin • Gastrin • Is secreted by G cells in duodenum • When exposed to incompletely digested proteins • Promotes increased stomach motility • Stimulates acids and enzyme production • Secretin • Is released when chyme arrives in duodenum • Increases secretion of bile and buffers by liver and pancreas • Gastric Inhibitory Peptide (GIP) • Is secreted when fats and carbohydrates enter small intestine • Cholecystokinin (CCK) • Is secreted in duodenum • When chyme contains lipids and partially digested proteins • Accelerates pancreatic production and secretion of digestive enzymes • Relaxes hepatopancreatic sphincter and gallbladder • Ejecting bile and pancreatic juice into duodenum • Vasoactive Intestinal Peptide (VIP) • Stimulates secretion of intestinal glands • Dilates regional capillaries • Inhibits acid production in stomach • Enterocrinin • Is released when chyme enters small intestine • Stimulates mucin production by submucosal glands of duodenum • Intestinal Absorption • It takes about 5 hours for materials to pass from duodenum to end of ileum • Movements of the mucosa increase absorptive effectiveness • Stir and mix intestinal contents • Constantly change environment around epithelial cells The Large Intestine • The Large Intestine • Is horseshoe shaped • Extends from end of ileum to anus • Lies inferior to stomach and liver • Frames the small intestine • Also called large bowel • Is about 1.5 meters (4.9 ft) long and 7.5 cm (3 in.) wide • Functions of the Large Intestine • Reabsorption of water • Compaction of intestinal contents into feces • Absorption of important vitamins produced by bacteria • Storage of fecal material prior to defecation • Parts of the Large Intestine • Cecum • The pouchlike first portion • Colon • The largest portion • Rectum • The last 15 cm (6 in.) of digestive tract • The Cecum • Is an expanded pouch • Receives material arriving from the ileum • Stores materials and begins compaction • Appendix • Also called vermiform appendix • Is a slender, hollow appendage about 9 cm (3.6 in.) long • Is dominated by lymphoid nodules (a lymphoid organ) • Is attached to posteromedial surface of cecum • Mesoappendix connects appendix to ileum and cecum • The Colon • Has a larger diameter and thinner wall than small intestine • The wall of the colon • Forms a series of pouches (haustra) • Haustra permit expansion and elongation of colon • Colon Muscles • Three longitudinal bands of smooth muscle (taeniae coli) • Run along outer surfaces of colon • Deep to the serosa • Similar to outer layer of muscularis externa • Muscle tone in taeniae coli creates the haustra • Serosa of the Colon • Contains numerous teardrop-shaped sacs of fat • Fatty appendices or epiploic appendages • Four Regions of the Colon • Ascending colon • Transverse colon • Descending colon • Sigmoid colon • Ascending Colon • Begins at superior border of cecum • Ascends along right lateral and posterior wall of peritoneal cavity • To inferior surface of the liver and bends at right colic flexure (hepatic flexure) • Transverse Colon • Crosses abdomen from right to left; turns at left colic flexure (splenic flexure) • Is supported by transverse mesocolon • Is separated from anterior abdominal wall by greater omentum • Descending Colon • Proceeds inferiorly along left side to the iliac fossa (inner surface of left ilium) • Is retroperitoneal, firmly attached to abdominal wall • Sigmoid Colon • Is an S-shaped segment, about 15 cm (6 in.) long • Starts at sigmoid flexure • Lies posterior to urinary bladder • Is suspended from sigmoid mesocolon • Empties into rectum • Blood Supply of the Large Intestine • Receives blood from tributaries of: • Superior mesenteric and inferior mesenteric arteries • Venous blood is collected from: • Superior mesenteric and inferior mesenteric veins • The Rectum • Forms last 15 cm (6 in.) of digestive tract • Is an expandable organ for temporary storage of feces • Movement of fecal material into rectum triggers urge to defecate • The Anal Canal • Is the last portion of the rectum • Contains small longitudinal folds called anal columns • Anus • Also called anal orifice • Is exit of the anal canal • Has keratinized epidermis like skin • Anal Sphincters • Internal anal sphincter • Circular muscle layer of muscularis externa • Has smooth muscle cells, not under voluntary control • External anal sphincter • Encircles distal portion of anal canal • A ring of skeletal muscle fibers, under voluntary control • Histology of the Large Intestine • Lacks villi • Abundance of mucous cells • Presence of distinctive intestinal glands • Are deeper than glands of small intestine • Are dominated by mucous cells
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