Week 5 Chapt 26 Digestive Part 2 PDF

DIGESTIVE CHAPTER 26 PART 2  Gross Anatomy of the Lower GI Tract Organs and Accessory Digestive Organs – Small Intestine Small intestine Small bowel, long tube inferior to stomach and located medially in abdominal cavity Ingested nutrients reside in small intestine at least 12 hours...

DIGESTIVE CHAPTER 26 PART 2  Gross Anatomy of the Lower GI Tract Organs and Accessory Digestive Organs – Small Intestine Small intestine Small bowel, long tube inferior to stomach and located medially in abdominal cavity Ingested nutrients reside in small intestine at least 12 hours Absorbs most nutrients and large percentage of water, electrolytes, and vitamins Gross anatomy of the small intestine Coiled, thin-walled tube Extends from pylorus to cecum of large intestine Consists of 3 segments: duodenum, jejunum, ileum  Small Intestine – Segments Duodenum First segment of small intestine, originates at pyloric sphincter C-shape around head of pancreas Continuous with jejunum at duodenojejunal flexure Mostly retroperitoneal (initial portion is intraperitoneal) Receives chyme from stomach Receives accessory gland secretions from liver, gallbladder, and pancreas  Small Intestine – Segments Jejunum Middle region of small intestine Two-fifths of total length of small intestine Primary region for chemical digestion and nutrient absorption Intraperitoneal and suspended by mesentery proper  Small Intestine – Segments Ileum Last region of small intestine Forms three-fifths of small intestine Distal end terminates at ileocecal valve Sphincter controlling entry of materials into large intestine Intraperitoneal and suspended by mesentery proper Continues absorption of digested material Small Intestine Tunics Figure 26.16a Circular folds Internal folds of mucosal and submucosal tunics of small intestine Increase surface area to increase nutrient absorption “Speed bumps” to slow movement of chyme More numerous in duodenum and jejunum, less in ileum Histology of Small Intestine Villi Fingerlike projections of mucosa Larger and most numerous in jejunum Epithelium covers lamina propria Increases surface area for absorption and secretion Contains an arteriole, capillary network, venule Figure 26.16b  Lacteal Histology of Small Intestine Lymphatic capillary within villus Responsible for absorbing lipids and lipid-soluble vitamins Microvilli Extensions of plasma membrane of simple columnar epithelial cells Increases surface area of small intestine Microscopic brush border Various enzymes embedded here, brush border enzymes (aid in digestion) Proteins for transport of digestion products also embedded here Figure 26.16b  Intestinal Villus Secrete intestinal juice Key enzyme in protein digestion CCK and Secretin Figure 26.16c  Intestinal Villus Small intestine secretions – not shown on previous slide Submucosal gland (AKA Brunner’s Gland) Produces alkaline mucus secretion protecting duodenum from chime Only found in duodenum Figure 26.16c Small Intestine Motility Smooth muscle of small intestine: Mixes chyme with gland secretions, Segmentation, backward-and-forward motion Segmentation more common in earlier stages of small intestine than peristalsis Moves chyme against new areas of brush border Chyme is propelled through small intestine by peristalsis Figure 26.16c Small Intestine Motility Regulation of small intestine motility during the intestinal phase Contractions initiated by pacemaker cells and spread through muscularis via gap junctions (similar to stomach) Spontaneously depolarize (more frequent in duodenum than ileum) Force of contraction regulated by both ENS and ANS Peristalsis is prevalent late in intestinal phase Initiated by motilin, released from duodenum Successive waves of contractions migrating motility complex Figure 26.16c Repeats until all content moved to large Moving Chyme from Small Intestine into Large Intestine Involves Gastroileal reflex (initiated when food enters stomach) Ileum Contracts Duodenum Ileocecal sphincter relaxes (CCK helps Jejunum cause this) and cecum relaxes Moves contents from Ileocecal ileum to cecum in valve Ileum response to food in stomach Ileocecal valve cecum contracts to prevent Appendix backflow Figure 26.16c  Accessory Digestive Organs 3 accessory digestive organs release secretions into the duodenum (Liver, Gallbladder and Pancreas) Gallbladder Saclike organ attached to inferior surface of liver Stores, concentrates, and releases bile produced in liver Bile aids in digestion of fats 3 tunics: inner mucosa, middle muscularis, external serosa Mucosa with folds that allow distension of wall Connected to common bile duct by cystic duct Pancreas Endocrine function Produces and secretes insulin and glucagon Exocrine function Produces pancreatic juice to assist with digestive activities Figure 26.18  Accessory Digestive Organs Biliary apparatus Network of ducts draining left and right lobes of Liver Include left and right hepatic ducts Merge to form single common hepatic duct Merges with cystic duct from gallbladder to form common bile duct Extends inferiorly to the duodenum Figure 26.18 Anatomy of the Liver: Anterior and Posterior Views Liver Accessory digestive organ and largest internal organ Right upper quadrant of abdomen immediately inferior to diaphragm Production of bile is main function Gross anatomy of the liver: Covered by Connective Tissue capsule and layer of visceral peritoneum Except for a small bare area on diaphragmatic surface Inferior vena cava seen on postero-inferior view Ligamentum venosum, remnant of ductus venosus in embryo Figure 26.19a  Anatomy of the Liver: Anterior and Posterior Views Porta hepatis Where blood, lymph vessels, bile ducts, nerves, enter and leave liver Hepatic artery Branch of celiac trunk Carries oxygenated blood to liver Hepatic portal vein Carries deoxygenated and nutrient-rich blood from capillary beds of GI tract, spleen, pancreas Brings 75% of blood to liver Blood mixes as passes through hepatic (liver) lobules Hepatic veins Empty into inferior vena cava As blood is transported through hepatic sinusoids towards the hepatic veins: Nutrients and oxygen absorbed, enter hepatocytes Stellate cells (Kupffer cells) macrophages that clear harmful substances Figure 26.19a Clinical View: Gallstones (Cholelithiasis) Condensations of cholesterol or calcium and bile salts Majority asymptomatic until lodged in neck of cystic duct Gallbladder becomes inflamed (cholecystitis) Risk factors Female sex, obesity, age, Caucasian Symptoms Severe pain in right hypochondriac region Nausea, vomiting, indigestion, bloating Symptoms worse after fatty meal May require surgical removal, cholecystectomy  Accessory Digestive Organs and Pancreas Ducts Endocrine function: Produces and secretes insulin and glucagon Exocrine function: Produces pancreatic juice to assist with digestive activities Pancreatic juice Formed from secretions of acinar cells and pancreatic duct cells Alkaline fluid, containing mostly water, HCO3– and digestive enzymes Pancreatic amylase to digest starch Pancreatic lipase to digest triglycerides Inactive proteases that digest proteins when activated Nucleases for digestion of nucleic acids Clinical View: Pancreatic Cancer Cancer of the pancreatic cells, typically exocrine cells Prognosis is good with early detection, but early detection is difficult because: There is no screening test Absence of signs and symptoms in the early stages of the disease Symptoms in later stages include abdominal pain, jaundice, loss of appetite, weight loss Pancreatic cancer is often fatal because usually detected late Regulation of Pancreatic Secretions Three Main Ways in Which Pancreatic Secretions are Activated 1. Vagal (Vagus Nerve) innervation to the pancreas stimulates the secretion of enzymes. This happens when we see, smell or taste food, or when the stomach wall is stretched. 2. Acidic chyme entering the duodenum stimulates cells to release secretin. Secretin causes the pancreatic cells to secrete the alkaline parts of the pancreatic juices. 3. The fatty acids and protein present in the chyme, combined with the acidic pH, trigger cells in the duodenum to release the hormone cholecystokinin (CCK). This hormone  Ascendin Transver Descendi Sigmoid Cecum Rectum Anus g Colon se Colon ng Colon Colon Large Intestine Figure 26.23a Large Intestine Functions: Absorbs water and electrolytes from remaining digested material Watery chyme compacted into feces Stores feces until eliminated through defecation Contain resident flora Large Intestine The Gastrocolic reflex Reflex that controls peristalsis of the gastrointestinal tract. It involves an increase in peristalsis of the colon in response to stretch of the stomach by presence of food in it, as well as chemical processes starting in the duodenum. This reflex is responsible for the typical urge to defecate following a meal. Anal Canal Rectum Storage of fecal matter prior to defecation Rectal Valves Retain fecal matter during passing of gas Anal Canal Terminal centimeters of the large intestine Figure 26.23b  Clinical View: Appendicitis Inflammation of appendix Most due to fecal matter obstructing the appendix Appendix swells, blood supply compromised, bacterial growth May burst if untreated Causing dangerous infection, peritonitis Pain initially referred to T10 around umbilicus from smooth muscle Eventually involves peritoneum Pain localized to right lower quadrant Nausea or vomiting, abdominal tenderness, fever Surgically removed through appendectomy  Motility and Regulation of Large Intestine Peristalsis is weak and sluggish in large intestine compared to small intestine Churning Distension stimulates reflex contractions in muscularis layers Increase churning and move material to more distal portion Mass movements Powerful contractions Propel fecal material toward the rectum 2–3 times a day, often after a meal  Motility and Regulation of Large Intestine con’t Gastrocolic reflex Initiated by stomach distension Causes a mass movement of fecal matter through large intestine Defecation reflex Filling of rectum initiates urge to defecate Receptors signal to spinal cord Increases parasympathetic output to sigmoid colon and rectum Decreases output to internal (involuntary) anal sphincter Voluntary defecation Learned about age 3 Involves Valsalva maneuver Involves relaxation of external (voluntary) anal sphincter Figure 26.25  Carbohydrate Digestion Carbohydrates Monosaccharides, e.g., glucose, fructose, galactose Disaccharides, e.g., sucrose, maltose Disaccharides broken down into individual monosaccharides Polysaccharides, e.g., starch and cellulose Starch broken down into individual glucose molecules Main digestion sites: oral cavity and small intestine Absorption: via cotransport with Na+, and facilitated diffusion Enter the capillary bed in the villi Transported to the liver via the hepatic portal vein Enzymes used: salivary amylase, pancreatic amylase, and brush border enzymes  Protein Digestion Absorption: similar to carbohydrates – cotransport with sodium and facilitated diffusion Enzymes acting in stomach: Pepsin Enzymes acting in the small intestine Pancreatic enzymes – trypsin, chymotrypsin, and carboxypeptidase Brush border enzymes – aminopeptidases, carboxypeptidases, and dipeptidases.  Lipid Digestion Lipid breakdown in the stomach Lingual lipase Component of saliva in the mouth Activated when reaches the stomach Gastric lipase Produced by chief cells Together digest 30% of triglycerides to diglyceride and fatty acid Neither requires participation of bile salts Lipid breakdown in the small intestine Pancreatic lipase Enzyme produced by pancreas and released into duodenum Digests triglycerides into monoglycerides and two fatty acids Requires separation of large lipid droplets into smaller droplets, emulsification via bile salts  Lipid Digestion Emulsified fat droplets are called micelles  Nucleic Acid Digestion Nucleic acids are part of DNA and RNA Absorption: active transport via membrane carriers Absorbed in villi and transported to liver via hepatic portal vein Enzymes used: pancreatic ribonucleases and deoxyribonuclease in the small intestines  Water and Electrolyte Absorption Small intestine is location of most water, electrolytes, and vitamin absorption from diet Water absorption Small intestine absorbs almost all ingested water (average 8 out of 9 liters) Large intestine absorbs some Rest passed in feces Electrolyte absorption Small intestine absorbs almost all electrolytes that enter Most absorption is unregulated, dependent on diet Iron has controlled absorption Hepcidin is a hormone released from liver Inhibits iron absorption If iron levels are low, hepcidin levels are decreased, allowing for greater iron absorption  Vitamin Absorption Vitamin absorption Fat-soluble vitamins (A, D, E, K) absorbed in small intestine along with lipids within micelles Water-soluble vitamins (B and C) absorbed through diffusion and active transport B12 is large, so absorbed by receptor- mediated endocytosis B12 requires intrinsic factor (formed by parietal cells in stomach)