Chapter 23 Intestines and Absorption
Chapter 23 Intestines and Absorption KNR 182
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HUMAN ANATOMY amp PHYSIOLOGY KNR 182 Digestive System Chapter 23 Pancreas The pancreas has a dual function as both an endocrine gland and exocrine gland The exocrine function is to secrete digestive juice called pancreatic juice Structure of the Pancreas Copyright The McGrawHill Companies Inc Permission required for reproduction or display Left hepatic duct Common hepatic duct Right hepatic duct Cystic duct Bile duct Gallbladder Pancreatic duct 7 7 l Pyloric sphincter quot5 w 1 9 36 15 f w 5 Mquot 1 Minor duodenal papilla Duodenum Tail of pancreas Pancreatic Major duodenal duct papilla Sphincter muscles V j l i i j r 3 39 l Cl Bile duct Head of pancreas Major duodenal papilla Intestinal lumen Hepatopancreatic Hepatopancreatic ampulla sphincter Pancreatic Juice Pancreatic juice contains enzymes that digest carbohydrates fats proteins and nucleic acids and include Pancreatic amylase splits glycogen into disaccharides Pancreatic pancrease Amyl starch ase enzyme Pancreatic lipase breaks down triglycerides o Lipids don t get broken down until they reach the small intestine and the pancreatic lipase Trypsin chymotrypsin anol carboxypeptidase digest proteins Nucleases digest nucleic acids Bicarbonate ions make pancreatic juice alkaline Helps to increase the pH Regulation of Pancreatic Secretion Copyright The McGraw Hill Companies Inc Permission required for reproduction or display Acidic chyme enters duodenum quot39 1 N v 39 am A 4 Pancreatic juice rich 33953 in bicarbonate ions Mfr passes down Q quot pancreatic duc quot Iheuo u I I P Secretin stimulates pancreas to secrete bicarbonate ions Intestinal mucosa releases secretin into bloodstream Hormonal signals released into bloodstream Stimulation of effector organ Liver The liver is the largest internal organ It is located in the upperright abdominal quadrant just beneath the diaphragm All of the processing that occurs in the liver happens in the lobules Copyright The McGraw Hill Companies Inc Permission required for reproduction or display Gallbladder Inferior vena cava Coronary ligament Right lobe Quadrate lobe Le lobe Cystic duct Hepatic duct Hepatic artery Hepatic portal Right lobe Left lobe vein Round ligament Bile duct Gallbladder Inferior vena cava Caudate lobe a b Head and upper limb capillaries I Deoxygenated blood I Oxygenated blood Supe or vena cava Hepatic artery Inferior vena cava Hepatic vein Hepatic portal vein Liver Mesenteric artery Renal capillaries to intestine Renal efferent Renal afferent arterioles arterioles Common iliac artery Common iliac vein Lower limb capillaries Liver Functions The liver carries on many important metabolic activities including Produces glycogen from glucose Breaks down glycogen into glucose Converts noncarbohydrates to glucose Oxidizes fatty acids Synthesizes lipoproteins phospholipids and cholesterol Converts carbohydrates and proteins into fats Deaminating amino acids Forms urea Synthesizes plasma proteins Converts some amino acids to other amino acids Stores glycogen iron and vitamins A D and B12 Phagocytosis of worn out RBCs and foreign substances Removes toxins such as alcohol and certain drugs from the blood Produces Bile Composition of Bile Bile is a yellowishgreen liquid that hepatic cells continuously secrete Bile contains Water Bile salts Emulsify fats Help absorb fatty acids cholesterol and fatsoluble vitamins Bile pigments The result of the breakdown of red blood cells Cholesterol Electrolytes Functions of Bile Salts Bile salts aid digestive enzymes They reduce surface tension and break fat globules into droplets like soap or detergent and this is called emulsification They enhance absorption of fatty acids and cholesterol They help absorb fatsoluble vitamins A D E and K Bile salts are recycled as they return to the liver Gallbladder Stores and concentrates bile that is not needed immediately CCK is responsible for telling the gallbladder to contract Copyright The McGrawHill Companies Inc Permission required for reproduction or display Regulation of Bile Release Cholecystokinin CCK Copyright The McGrawHill Companies Inc Permission required for reproduction or display Cystic duct Common hepatic duct Gallbladder CCK stimulates muscular layer of gallbladder wall to contract Chyme with fat enters duodenum Bile duct Bile passes down the cystic duct and bile duct to duodenum Hepatopancreatic sphincter relaxes and bile enters duodenum Pancreatic duct 1 Cells from the b intestinal mucosa secrete the hormone cholecystokinin CCK into the bloodstream Duodenum Hormonal signals released into bloodstream Stimulation of effector organ Check your understanding Cirrhosis of the liver would most severely impact digestion of ligids Small Intestine Gross Anatomy Major organ of digestion and absorption 90 of absorption occurs in the small intestine 2 4 m long from pyloric sphincter to ileocecal valve Subdivisions 1 Duodenum top 2 Jejunum middle 3 lleum end leading to the colon Parotid land Mouth oral cavrty 9 Sublingual gland 39 Tongue Submandibular sa wary glands gland Esophagus Pharynx Stomach Pancreas Liver Sp39een Gallbladder Transverse colon Duodenum Descending colon Small Jejunum Ascending colon intestine Ileum Cecum Farg i Sigmoid colon Intestine Rectum Vermiform appendix Anus Anal canal Figure 231 Parts of the Small Intestine Copyright The McGrawHill Companies Inc Permission required for reproduction or display Stomach Duodenum Cecum Mesentery Appendix Ileum Structure of the Small Intestinal Wall Copyright The McGrawHill Companies Inc Permission required for reproduction or display Villus c of C39 i39 3 13 39 t 1 l 39 Simple columnar epithelium Lacteal Goblet cells Intestinal gland Arteriole Venule I O Lymph vessel Blood capillary network Copyright The McGrawHill Companies Inc Permission required for reproduction or display Villus Intestinal gland 9 w 3 J 1 39Qyng I n 1 1 1 The McGraw Hill Companies ncA Telser photographer 7 1c v quot r 39 1quot I gig1quot 6 Close up view of a villi Folds are in a circular form Creates a vortex spins food around a aiding In digestion Increases surface area Pquot ae curculares allowrng for better digestion Villi Villi increase the surface area even Submucosa more even better absorption Muscular layer A Circular muscle Longitudinal muscle Serosa Secretions of the Small Intestine In addition to mucussecreting goblet cells there are many specialized mucus secreting glands Brunner s glands that secrete a thick alkaline mucus in response to certain stimuli Enzymes in the membranes of the microcvilli include finally getting to monomers Peptidase breaks down peptides into amino acids Sucrase matase lactase break down disaccharides into monosaccharides Lipase breaks down fats into fatty acids and glycerol Enterokinase converts trypsinogen to trypsin Somatostatin hormone that inhibits acid secretion by stomach Choecystokinin hormone that inhibits gastric glandswhen chyme enters the stomach stimulates pancreas to release enzymes in pancreatic juice and stimulates the gallbladder to release bile Secretn stimulates the pancreas to release bicarbonate ions in pancreatic juice Nutrient Absorption in the Small Intestine Simplest form of ingested food molecules Via simple diffusion facilitated diffusion active transport or osmosis Transport differs depending on the monomer Monosaccharides Amino acids Fatty acids Ions and water Movements of Small Intestine Segmentation Mixing Wave like contractions that break apart chyme Peristaltic waves Move chyme to ileocecal sphincter Contraction anol refluxation to move the chime through the tube Peristaltic rush Due to overdistention or irritation Ex spicy food or food with a bacteriaeating too much food The small intestine will immediately want to get rid of it and not absorb it9 diarrhea because you cant absorb nutrients Check your understanding What is the primary stimulus for intestinal gland secretion Acidic content and distension of the intestinal wall Large Intestine Regions Cecum pouch with attached appendix Colon Rectum Anal canal Large Intestine Unique features Teniae coli Three bands of longitudinal smooth muscle in the muscularis Haustra Pocketlike sacs caused by the tone of the teniae coli Epiploic appendages Fatfilled pouches of visceral peritoneum I I ll 39 I nghtCOIIC LaftCOIIC hepatic quot quotxk quot splenic flexure flexure Q I r 39 Transverse Transverse i 39 mesocolon colon i 39 3 I Epiploic Superlor M K appendages mesenterIc I artery i g Descending Haustrum K a I A a 1 colon Ascend I ng l v x X colon l 39 r i N 39 Cut edge of j TenIae COII Heocecal x 2 Sigmoid colon valve 1 Cecum quot Vermiform appendix Rectum l Anal canal a Figure 2329a Ceoum First portion of large intestine Nearest Ileum Appendix Pouch in this region No known digestive function Colon Majority of the length of the large intestine Ascending Colon Transverse Colon Descending Colon Sigmoid Colon Greater omentum I v M i 3 A j Transverse colon Ax l f c Q Transverse 1 a l mesocolon l Mesentery I39 Descending colon 539 1 A zquot 39 J Jejunum Sigmoid mesocolon Sigmoid colon lleum C Figure 2330c Functions of the Large Intestine The large intestine Has little or no digestive func on AbSOrbS water and Lumen of large GIGCtrOIYteS intestine Secretes mucus GOb39et cells Houses intestinal flora Ed Reschke Forms feces Carries out defecation Structure of the Large Inal Wall lntest Inc Permission required for reproduction or display Hill Companies Copyright The McGraw Submuoosa 39 v 391 5 5 I h 723 4A 3339 L 1 J Ih lt a Muscular layer Serosa Ed ReschkePeter Arnold Movements of the Large Intestine Movements of the large intestine are similar to those of the small intestine It is slower and less frequent than that of the small intestine Movements include Mixing movements Peristalsismovement of residual chime Referred to as mass movements in large intestine Usualy fol0W meals Haustral contractions segmenting formation of feces Mainy in the first part of the large intestine Mass movements usually follow meals The defecation reflex relaxes the internal anal sphincter and then the external anal sphincter Rectum and Anus Rectum Three rectal valves stop feces from being passed with gas Allow you to pass gas without defecation Anal canal The last segment of the large intestine Sphincters Internal anal sphincter smooth muscle involuntary Not under conscious control External anal sphincter skeletal muscle voluntary You have control skeletal muscle The defecation reflex relaxes the internal and sphincter and then the external anal sphincter VIDEO Reflexes of the Colon Rectal valve Rectum Hemorrhoidal veins 2 Levator anI muscle Anal canal External anal sphincter A lnternal anal sphincter Anal columns Pectinate line Anal sinuses Anus b Figure 232 Motility of the Large Intestine Haustral contractions Slow segmenting movements Haustral sequentially contract in response to distension Motility of the Large Intestine Gastrooolio reflex Initiated by presence of food in the stomach Activates three to four slow powerful peristaltic waves per day in the colon mass movements Defecation Mass movements force feces into the rectum Distension initiates spinal defecation reflex through stretch receptors Parasympathetic signals Stimulate contraction of the sigmoid colon and rectum to contract Move feces down into anal canal Relax the internal anal sphincter Conscious control allows relaxation of external anal sphincter lmpulses from cerebral cortex conscious control Voluntary motor nerve to external anal sphincter l 1 External anal sphincter skeletal muscle I Sensory nerve fibers 1 Distension or stretch of the rectal walls due to movement of feces into the rectum stimulates stretch receptors there The receptors transmit signals along afferent fibers to spinal cord neurons 9 A spinal reflex is initiated in which parasympathetic motor efferent fibers stimulate contraction of the rectal walls and relaxation of the internal anal sphincter Stretch receptors in wall Involuntary motor nerve parasympathetic division Internal anal sphincter smooth muscle If it is convenient to defecate voluntary motor neurons are inhibited allowing the external anal sphincter to relax so that feces may pass Figure 2331 Feces Feces material that body can t use is composed of materials not digested or absorbed and include Water Electrolytes Mucus All of the secretions from the alimentary canal Bacteria Bile pigments altered by bacteria provide the color Bile that is created in gallbladder produced for digestion of lipids The pungent odor is produced by bacterial compounds including Phenol Hydrogen sulfide lndole Skatole Ammonia VIDEO Are your Poop and Pee Normal Dr Oz Check your understanding In terms of digestion the large intestine s greatest contribution is Absorption of water GI tract regulatory mechanisms 1 Mechanoreceptors and chemoreceptors 1 Through out alimentary canal Respond to stretch changes in osmolality and pH and presence of substrate and end products of digestion Initiate reflexes that Activate or inhibit digestive glands Stimulate smooth muscle to mix and move lumen contents GI tract regulatory mechanisms 2 Intrinsic and extrinsic controls Enteric nerve plexuses gut brain initiate short reflexes in response to stimuli in the GI tract 2nol brain because there are a lot of nerve endings and impulses located here Long reflexes in response to stimuli inside or outside the GI tract involve CNS centers and autonomic nerves Hormones from cells in the stomach and small intestine stimulate target cells in the same or different organs Central nervous system L and extrinsic autonomic nerves sight smell taste External stimuli thought of food L f Long reflexes1 Afferent impulses Efferent impulses v1 Internal Chemoreceptors Local intrinsic EffectOI39S GI tract osmoreceptors or nerve plexus Smooth muscle stimuli mechanoreceptors gut brain of glands L Short reflexes 1 Gastrointestinal Resp se Change In wall Site of short contractile or reflexes secretory actIVIty L 1 Figure 234 Chemical Digestion Catabolic Enzymatic Hydrolysis Chemical Digestion and Absorption of Carbohydrates Digestive enzymes Salivary amylase pancreatic amylase and brush border enzymes dextrinase glucoamylase lactase maltase and sucrase Chemical Digestion and Absorption of Carbohydrates Absorption Secondary active transport cotransport with Na Facilitated diffusion of some monosaccharides Enter the capillary beds in the villi Transported to the liver via the hepatic portal vein USE AS SUMMARY STUDY OVERVIEW Carbohydrate digestion Enzymes Site of Foodstuff and source action Path of absorption Glucose and galactose Starch and dlsaccharldes are absorbed via Salivary Mouth cotransport with amylase SOdium ions lt Pancreatic Small Fruftose passe Via Oligosaccharides amylase intestine faCIlItated dIfoSIon and disaccharides A monosaccharldes I leave the epithelial l i l 39 Brush border Nu Small cells via facilitated Lactose Maltose Sucrose enzymes in a w intestine di USion enter the small intestine capillary blood in the R Al dextrinase gluco villi and are Galactose Glucose Fructose amylase lactase transported to the liver maltase and sucrase via the hepatic portal veIn Figure 2332 1 of 4 Chemical Digestion and Absorption of Proteins Enzymes pepsin in the stomach Pancreatic proteases Trypsin chymotrypsin and carboxypeptidase Brush border enzymes Aminopeptidases carboxypeptidases and dipeptidases Absorption of amino acids is coupled to active transport of Na Pancreatic proteases Lumen of intestine L Amino acids of protein fragments Brush border enzymes Apical membrane microvilli CD Proteins and protein fragments are digested to amino acids by pancreatic proteases trypsin chymotrypsin and carboxy peptidase and by brush border enzymes carboxypeptidase aminopeptidase and dipeptidase of mucosal cells The amino acids are then absorbed by active transport into the absorptive cells and move to their opposite side transcytosis The amino acids leave the villus epithelial cell by facilitated diffusion and enter the capillary via intercellular clefts Figure 2333 Protein digestion Foodstuff Protein Large polypeptides 1 Small polypeptides small peptides 4 Amino acids some dipeptides and tripeptides Enzymes and source Pepsin stomach glands in presence of HCI Pancreatic enzymes trypsin chymotrypsin carboxypeptidase Brush border enzymes aminopeptidase carboxypeptidase and dipeptidase Site of action Path of absorption 0 Amino acids are absorbed by cotransport with StomaCh sodium ions Some dipeptides and tripeptides are absorbed Small via cotransport with Ht intestine and hydrolyzed to amino acids within the cells 0 Amino acids leave the epithelial cells by Smquot facilitated diffusion enter intestine the capillary blood in the villi and are transported to the liver via the hepatic portal vein Figure 2332 2 of 4 Chemical Digestion and Absorption of Lipids Pretreatment emulsification by bile salts Enzymes pancreatic lipase Absorption of glycerol and short chain fatty acids Absorbed into the capillary blood in villi Transported via the hepatic portal vein Chemical Digestion and Absorption of Lipids Absorption of monoglycerides and fatty acids Cluster with bile salts and lecithin to form micelles Released by micelles to diffuse into epithelial cells Combine with proteins to form chylomicrons Enter lacteals and are transported to systemic circulation lt 39 G Large fat globules are emulsified Bile salts physically broken up into smaller fat droplets by bile salts in the duodenum C2 Digestion of fat by the pancreatic enzyme lipase yields free fatty acids and monoglycerides These then associate with bile salts to form micelles which ferry them to the intestinal mucosa Micelles made up of fatty acids monoglycerides and bile salts Fatty acids and monoglycerides leave micelles and diffuse into epithelial cells There they are recombined and packaged with other lipoid substances and proteins to form chylomicrons a 1 Chylomicrons are extruded from the l epithelial cells by exocytosis The cell if X g I chylomicrons enter lacteals They are smal39 actea carried away from the intestine by lymph intestine 39 Figure 2334 Fat digestion Foodstuff Enzymes and source Unemulsified fats lt Emulsification by gr the detergent action of bile salts ducted in from the liver 4 Pancreatic Hpases l and fatty acids l Monoglycerides Glycerol and fatty acids Site of ac on Small intestine Small intestine Path of absorption Fatty acids and monoglycerides enter the intestinal cells via diffusion Fatty acids and monoglycerides are recombined to form triglycerides and then combined with other lipids and proteins within the cells and the resulting chylomicrons are extruded by exocytosis The chylomicrons enter the lacteals of the villi and are transported to the systemic circulation via the lymph in the thoracic duct Some shortchain fatty acids are absorbed move into the capillary blood in the villi by diffusion and are transported to the liver via the hepatic portal vein Figure 2332 3 of 4 Water Absorption 95 is absorbed in the small intestine by osmosis Net osmosis occurs whenever a concentration gradient is established by active transport of solutes Water uptake is coupled with solute uptake
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