Exercise 38 -The Digestive system 3/1/2011 lab 2 groups of organs compose the digestive system Gastrointenstinal (GI) tract or alimentary canal mouth, most of pharynx, esophagus, stomach, small intestine, and large intestine Accessory digestive organs teeth, tongue, salivary glands, liver, gallbladder, and
pancreas Organs of the digestive system 6 functions of the digestive system 1. 2. 3. 4. Ingestion Secretion of water, acid, buffers, and enzymes into lumen Mixing and propulsion
Digestion 5. 6. Mechanical digestion churns food Chemical digestion hydrolysis Absorption passing into blood or lymph Defecation elimination of feces Layers of the GI tract Wall of GI tract from lower esophagus to anal canal has same basic 4 layers Mucosa inner lining
1. Epithelium protection, secretion, absorption Lamina propria connective tissue with blood and lymphatic vessels and mucosa-associated lymphatic tissue (MALT) Muscularis mucosae thin layer of smooth muscle making folds to increase surface area Submucosa
2. Connective tissue binding mucosa to muscularis Contains many blood and lymphatic vessels Submucosal plexus Layers of the GI tract 3. Muscularis
Voluntary skeletal muscle found in mouth, pharynx, upper 2/3 of esophagus, and anal sphincter Involuntary smooth muscle elsewhere 4. Arranged in inner circular fibers and outer longitudinal fibers Myenteric plexus between muscle layers Serosa
Outermost covering of organs suspended in abdominopelvic cavity Also called visceral peritoneum Esophagus lacks serosa has adventitia Layers of the gastrointestinal tract Neural innervation Enteric nervous system (ENS) Intrinsic set of nerves - brain of gut Neurons extending from esophagus to anus 2 plexuses
Myenteric plexus GI tract motility Submucosal plexus controlling secretions Autonomic nervous system Extrinsic set of nerves Parasympathetic stimulation increases secretion and activity by stimulating ENS Sympathetic stimulation decreases secretions and activity by inhibiting ENS Organization of the enteric nervous system
Peritoneum Largest serous membrane of the body Divided into Parietal peritoneum lines wall of cavity Visceral peritoneum covers some organs Also called serosa
Space between is peritoneal cavity 5 major peritoneal folds Greater omentum, falciform ligament, lesser omentum, mesentery, and mesocolon Weave between viscera binding organs together Peritoneal Folds Peritoneal Folds Mouth
Oral or buccal cavity Formed by cheeks, hard and sot palates, and tongue Oral cavity proper is a space that extends from gums and teeth to fauces (opening between oral cavity and oropharynx) Salivary glands release saliva
Ordinarily, just enough is secreted to keep mouth and pharynx moist and clean When food enters mouth, secretion increases to lubricate, dissolve and begin chemical digestion 3 pairs of major salivary glands secrete most of the saliva Parotid, submandibular, and sublingual Structures of the mouth (oral cavity) The three major salivary glandsparotid, sublingual, and submandibular Saliva
Saliva Mostly water 99.5% 0.5% solutes ions, dissolved gases, urea, uric acid, mucus, immunoglobulin A, lysozyme, and salivary amylase (acts on starch) Not all salivary glands produce the same saliva Salivation Controlled by autonomic nervous system Parasympathetic stimulation promotes secretion of moderate amount of saliva Sympathetic stimulation decreases salivation Tongue and Teeth
Tongue Accessory digestive organ Skeletal muscle covered by mucous membrane Maneuvers food for chewing, shapes mass, forces food back for swallowing Lingual glands secrete salivary lipase
Teeth or dentes Accessory digestive organ 3 major regions crown, root, and neck Dentin of crown covered by enamel 2 dentitions deciduous and permanent teeth A typical tooth and surrounding structures Digestion in the mouth
Mechanical digestion in the mouth Chewing or mastication Food manipulated by tongue, ground by teeth, and mixed with saliva Forms bolus Chemical digestion in the mouth Salivary amylase secreted by salivary glands acts on
starches Only monosaccharides can be absorbed Continues to act until inactivated by stomach acid Lingual lipase secreted by lingual glands of tongue acts on triglycerides Becomes activated in acidic environment of stomach Pharynx
Passes from mouth into pharynx 3 parts Nasopharynx Oropharynx Functions only in respiration
Digestive and respiratory functions Laryngopharynx Digestive and respiratory functions Esophagus Secretes mucous, transports food no enzymes produced, no absorption Mucosa protection against wear and tear
Submucosa Muscularis divided in thirds Superior 1/3 skeletal muscle Middle 1/3 skeletal and smooth muscle Inferior 1/3 smooth muscle 2 sphincters upper esophageal sphincter (UES) regulates movement into esophagus, lower esophageal sphincter (LES) regulates movement into stomach Adventitia no serosa attaches to surroundings
Histology of the esophagus Deglutition Act of swallowing Facilitated by secretions of saliva and mucus Involves mouth, pharynx, and esophagus 3 stages
Voluntary bolus passed to oropharynx Pharyngeal involuntary passage through pharynx into esophagus Esophageal involuntary passage through esophagus to stomach Peristalsis pushes bolus forward Deglutition (swallowing) Stomach Serves as mixing chamber and holding reservoir
4 main regions Cardia, fundus, body, pylorus Same 4 layers Mucosa gastric glands open into gastric pits 3 types of exocrine gland cells mucous neck cells (mucus), parietal cells (intrinsic factor and HCl), and chief
cells (pepsinogen and gastric lipase) G cell endocrine cell secretes gastrin Submucosa Muscularis additional 3rd inner oblique layer Serosa part of visceral peritoneum External and internal anatomy of the stomach Histology of the stomach Mechanical and Chemical Digestion Mechanical digestion
Mixing waves gentle, rippling peristaltic movements creates chyme Chemical digestion Digestion by salivary amylase continues until inactivated by acidic gastric juice Acidic gastric juice activates lingual lipase
Digest triglycerides into fatty acids and diglycerides Parietal cells secrete H+ and Cl- separately but net effect is HCl Kills many microbes, denatures proteins Chemical Digestion Chemical digestion (cont.) Pepsin secreted by chief cells digest proteins
Secreted as pepsinogen Gastric lipase splits triglycerides into fatty acids and monoglycerides Small amount of nutrient absorption Some water, ions, short chain fatty acids, certain drugs (aspirin) and alcohol Pancreas
Lies posterior to greater curvature of stomach Pancreatic juice secreted into pancreatic duct and accessory duct and to small intestine Pancreatic duct joins common bile duct and enters duodenum at hepatopancreatic ampulla Histology 99% of cells are acini
Exocrine Secrete pancreatic juice mixture of fluid and digestive enzymes 1% of cells are pancreatic islets (islets of Langerhans) Endocrine Secrete hormones glucagon, insulin, somatostatin, and pancreatic polypeptide
Relation of the pancreas to the liver, gallbladder, and duodenum Pancreatic juice 1200-1500ml daily Mostly water Sodium bicarbonate buffers acidic stomach chyme Enzymes
Pancreatic amylase Proteolytic enzymes trypsin (secreted as trypsinogen), chymotrypsin (chymotrypsinogen), carboxypeptidase (procarboxypeptidase), elastase (proelastase) Pancreatic lipase Ribonuclease and deoxyribonuclease Liver and gallbladder Liver is the heaviest gland of the body Liver is composed of
Hepatocytes major functional cells of liver Bile canaliculi ducts between hepatocytes that collect bile Wide variety of metabolic, secretory, and endocrine functions secrete bile (excretory product and digestive secretion) Exits livers as common hepatic duct, joins cystic duct from gallbladder to form common bile duct
Hepatic sinusoids highly permeable blood capillaries receiving oxygenated blood from hepatic artery and deoxygenated nutrientrich blood from hepatic portal vein 3 different ways to organize units Hepatic acinus preferred method Hepatocytes arranged in 3 zones around short axis with no sharp boundaries Histology of the Liver Histology of the Liver Gallbladder
Contraction of smooth muscle fibers eject contents of gall bladder into cystic duct Functions to store and concentrate bile produced by the liver until it is needed in the small intestine Absorbs water and ions to concentrate bile up to ten-fold Hepatic blood flow
Liver receives blood from Hepatic artery carrying oxygenated blood Hepatic portal vein carrying deoxygenated blood with newly absorbed nutrients and possibly drugs, microbes or toxins from GI tract Role and composition of bile
Hepatocytes secrete 800-1000mL of bile daily Mostly water, bile salts, cholesterol, lecithin, bile pigments and several ions Partially excretory product/ partially digestive secretion Bilirubin principal bile pigment Derived from heme of recycled RBCs Breakdown product stercobilin gives feces brown color
Bile salts play role in emulsification Also aid in absorption of lipids following digestion Small intestine 3 regions duodenum, jejunum, and ileum Same 4 layers 1. Mucosa
4. Completely surrounds except for major portion of duodenum Anatomy of the small intestine Special structural features increase surface area for digestion and absorption Circular folds
Permanent ridges of mucosa and submucosa Cause chyme to spiral Villi Fingerlike projections of mucosa Contains arteriole, venule, blood capillary, and lacteal Microvilli
Projects of apical membrane of absorptive cells Brush border with brush border enzymes Histology of the small intestine Histology of the duodenum and ileum Intestinal juice and brushborder enzymes Intestinal juice
1-2L daily Contains water and mucus, slightly alkaline Provide liquid medium aiding absorption Brush border enzymes Inserted into plasma membrane of absorptive cells Some enzymatic digestion occurs at surface rather than just in lumen -dextrinase, maltase, sucrase, lactase, aminopetidase,
dipeptidase, nucleosidases and phosphatases Mechanical Digestion Governed by myenteric plexus Segmentations Localized, mixing contractions Mix chyme and bring it in contact with mucosa for absorption
Migrating motility complexes (MMC) Type of peristalsis Begins in lower portion of stomach and pushes food forward Chemical digestion Carbohydrates
Pancreatic amylase -dextrinase, sucrase, lactase, maltase in brush border Ends with monosaccharides which can be absorbed Proteins Trypsin, chymotrypsin, carboxypeptidase, and elastase from pancreas Aminopeptidase and dipeptidase in brush border Lipids and Nucleic Acids
Lipids Pancreatic lipase most important in triglyceride digestion Emulsification by bile salts increases surface area Amphipathic hydrophobic and hydrophilic regions Nucleic acids Ribonuclease and deoxyribonuclease in pancreatic juice
Nucleosidases and phosphatases in brush border Absorption of: Monosaccharides All dietary carbohydrates digested are absorbed Only indigestible cellulose and fibers left in feces Absorbed by facilitated diffusion or active transport into blood
Amino acids, dipetides and tripeptides Most absorbed as amino acids via active transport into blood of absorbed amino acids come from proteins in digestive juice and dead mucosal cells Lipids All dietary lipids absorbed by simple diffusion Short-chain fatty acids go into blood for transport
Long-chain fatty acids and monoglycerides Large and hydrophobic Bile salts form micelles to ferry them to absorptive cell surface Reform into triglycerides forming chylomicrons Leave cell by exocytosis Enter lacteals to eventually enter blood with protein coat of chylomicron keeping them suspended and separate Absorption of digested nutrients
in the small intestine Absorption of: Electrolytes Vitamins
From GI secretions or food Sodium ions (Na+) reclaimed by active transport Other ions also absorbed by active transport Fat-soluble vitamins A, D, E, and K absorbed by simple diffusion and transported with lipids in micelles Most water-soluble vitamins also absorbed by simple diffusion Water 9.3L comes from ingestion (2.3L) and GI secretions (7.0L) Most absorbed in small intestine, some in large intestine
Only 100ml excreted in feces All water absorption by osmosis Daily volumes of fluid ingested, secreted, absorbed, and excreted from the GI tract Large intestine
Overall function to complete absorption, produce certain vitamins, and form and expel feces 4 major regions cecum, colon, rectum, and anal canal Ileocecal sphincter between small and large intestine Colon divided into ascending, transverse, descending and sigmoid Opening of anal canal (anus) guarded by internal anal sphincter of smooth muscle and external anal sphincter of skeletal muscle Anatomy of the large intestine Large Intestine
Same 4 layers Mucosa mostly absorptive and goblet cells Submucosa Muscularis
No circular folds or villi Does have microvilli Longitudinal muscle modified to form teniae coli Forms haustra pouches Serosa Digestion of the Large Intestine Mechanical digestion
Haustral churning Peristalsis Mass peristalsis drives contents of colon toward rectum Chemical digestion Final stage of digestion through bacterial action
Ferment carbohydrates, produce some B vitamins and vitamin K Mucus but no enzymes secreted Remaining water absorbed along with ions and some vitamins Histology of the large intestine Histology of the large intestine Phases of digestion
Cephalic phase Gastric phase Smell, sight, thought or initial taste of food activates neural centers prepares mouth and stomach for food to be eaten Neural and hormonal mechanisms promote gastric secretion and motility Intestinal phase
Begins when food enter small intestine Slows exit of chyme from stomach Stimulates flow of bile and pancreatic juice The gastric phase of digestion
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