Digestive System Study Guide Ingestion Intake of food Digestion Mechanical Chemical breakdown Absorption Uptake of nutrients Defecation elimination General Anatomy Digestive Tract aka Alimentary Canal muscular tube from mouth to anus digests and absorbs Accessory Organs teeth tongue salivary glands gallbladder liver pancreas Microscopic Anatomy 4 layers Mucosa inner lining Submucosa contains blood and lymph vessels Muscularis Externa 2 layers responsible for propelling food and residue through digestive tract circular inner layer longitudinal outer layer Serosa adventitia fibrous connective tissue that blends into the connective tissue of other organs pharynx esophagus and rectum Enteric Nervous System Nervous network between the esophagus stomach and intestines Regulates motility secretion and blood flow of the digestive tract Composed of 2 plexuses Submucosal Plexus controls secretory activity Myenteric Plexus controls muscularis externa and GI tract motility Peritoneum Serous membrane that lines the peritoneal cavity and covers the mesenteries and viscera Mesenteries double layer membrane functions to hold organs and store fat provide routes for nerves and lymph blood vessels Dorsal mesentery a translucent two layered membrane extending to the digestive tract Ventral mesentery may hang freely in the abdominal cavity of attach to the anterior abdominal wall or other organs Greater omentum hangs from greater curvature of stomach loosely covering the small intestine Lesser omentum extends the short distance from the liver to the lesser curvature of stomach Regulation of the Digestive Tract Short reflexes myenteric intrinsic stretching or chemicals stimulate contractions in the muscularis externa Long reflexes vasovagal extrinsic ANS control parasympathetic fibers of the vagus nerves stimulate digestive motility and secretion Oral Cavity aka mouth or buccal cavity Functions towards ingestion mastication chemical digestion swallowing Cheeks lips tongue palate teeth Saliva and Salivary Glands Saliva contains salivary amylase lingual lipase mucus lysozyme immunoglobulin A and electrolytes Intrinsic Salivary Glands small glands that supply a constant supply of saliva and lysozyme Lingual glands tongue labial glands inside of lips and buccal glands inside of cheeks Extrinsic Salivary Glands larger glands serous cells secrete a watery fluid rich in enzymes and electrolytes secrete 1 0 1 5 L day Parotid just beneath earlobes Submandibular on jaw Sublingual underneath tongue Salivary nuclei are sent signals from the medulla and pons regarding tactile touch pressure and taste salivation is also influenced by odor sight and thought parasympathetic stimulates salivation sympathetic inhibits salivation Pharynx muscular point where the digestive and respiratory tracts intersect deep muscle is skeletal muscle longitudinal superficial muscle is smooth circular divides into pharyngeal constrictors that force food downward during swallowing upper esophageal sphincter when food is not being swallowed the inferior constrictor remains contracted to exclude air from espophagus regarded as a physiological sphincter because it disappears at the time of death Esophagus long muscular tube that runs from the pharynx to the stomach Contains all GI tract layers Has esophageal glands in the submucosa secrete mucus for lubrication Cardiac orifice cardiac sphincter food enters stomach through this Deglutition swallowing coordinated by the swallowing center in the medulla and pons Buccal phase is voluntary control Pharyngeal esophageal phase involuntary bolus is driven downward by constriction of the pharyngeal constrictors Stomach functions for mechanical chemical digestion and liquefies food into chyme 4 Regions cardiac region fundic region body pyloric region Circulation stomach contains a gastric artery all blood drained from the stomach and intestines enters the hepatic portal system Micro Anatomy of Stomach mucularis externa is made up of 3 layers not 2 outer longitudinal middle circular layer and inner oblique Gastric mucosa lined with gastric pits depressions 2 or 3 tubular glands open into the bottom of the gastric pit and span the rest of the lamina propria tubular glands have different names depending on their location cardiac gastric or pyloric Mucosal Barrier protects mucosa from its own gastric secretions mucous coat contains bicarbonate rich mucus epithelial cell replacement occurs every 3 6 days tight junctions prevent leakage of gastric juice Gastric Pits contain different types of cells mucosal cells secrete mucus Regenerative cells divide rapidly and produce a continual supply of new cells Parietal cells secrete hydrochloric acid and intrinsic factor Enteroendocrine secrete hormones Gastric Secretions HCl functions to activate enzymes liquefy food convert ion and nonspecific resistance Bicarbonate reaction is cataylyzed by carbonic anhydrase Bicarbonate ions are exchanged for chloride ions HCl accumulates in stomach while bicarbonate ion accumulates in blood Alkaline tide high blood pH during digestion Pepsinogen several digestive enzymes are secreted as inactive proteins called zymogens zymogens are activated by HCl to form pepsin which digests proteins Digestive enzymes gastric lipase digests lipid chymosin Instrinsic factor glycoprotein that absorbs Vitamin B12 Chemical Messengers hormones paracrine secretions gut brain peptides VIP GIP NPY secretin CCK substance P Gastric Motility Swallowing center of medulla signals stomach to react Receptive relaxation response smooth muscle relaxes to accommodate food Peristaltic contractions pacemaker cells in longitudinal layer Pyloric sphincter controls chyme into small intestine Vomiting Forceful ejection of stomach and intestinal contents Involves muscular actions integrated by the emetic center in medulla Caused by overstretching chemical irritants trauma or pain psychological stimuli Retching is caused by thoracic expansion and abdominal contraction which creates a pressure difference to reverse peristalsis Regulation of Gastric Function nerve system and endocrine system collaboration Cephalic stomach responds to sight smell taste or thought of food sensory mental input converges on the hypothalamus which relays signals to medulla The vagus nerve fibers send sympathetic stimulation to the enteric nerve system of stomach which stimulates gastric secretion Gastric activity that begins when bolus enters stomach activates a short reflexes that