Physiology of GIT o Functions of GIT Parts of the GIT in proper sequence and purpose and function of each Digestion hydrolysis of energy nutrients Absorption passage of simple molecules across gut wall and into blood and lymph Elimination of wastes Protect body from harmful substances Metabolic processes o Oral cavity mouth and pharynx Entryway to Digestive tract Food is chewed by teeth to increase the surface area so that enzymes could come and break the bonds 3 pairs of salivary glands affected by Parasympathetic NS and SNS parotid water electrolytes and enzyme submandibular water electrolytes enzymes and mucus sublingual water electrolytes enzymes and mucus enzymes salivary amylase ptyalin principle enzyme of saliva o hydrolyzes alpha 1 4 bonds within starch amylopectin has alpha 1 6 linkages dextrin maltose maltotriose amylose maltose and maltitriose lingual lipase produced by lingual serous glands o hydrolyzed triacylglycerol in the stomach activity diminishes with age its activity in infants allow them to break down the fat in milk more efficiently mucus lubricates food and protects the oral mucosa contains glycoproteins antibacterial and antiviral components solutes lysosomes kill bacteria made by secretory glands in the epithelial lining o Esophagus Swallowing mechanism The esophageal sphincter relaxes allowing esophagus to open At the same time larynx moves up inducing the epiglottis to shift over the Food passes into the esophagus glottis keeping food from entering the trachea Once food is in esophagus larynx shifts downward allowing the glottis to reopen Food bolus Peristalsis moved the food through the esophagus and into the mouth Gastro esophageal sphincter GES or LES On swallowing the GES pressure drops relaxing the sphincter so that food may pass from esophagus to the stomach GES has a high tonic pressure higher than stomach that keeps it closed so that there is no reflux Diseases and conditions heartburn Gastric acid irritates esophageal mucosa and can lead to esophagitis o Stomach Esophagus cardia fundus body oxin pylorus antrum Cardia receives swallowed food Fundus Body serves as a reservoir for swallowed food and is the main production site Antrum 1 3 of stomach grinds and mixes the food forming chime provides of gastric juice strong peristalsis Extends from GES to duodenum Pyloric sphincter connects the stomach to the duodenum Empty it holds 2oz full it holds 37 52 oz Stomach mixes food with its circular longitudinal and oblique muscles When stomach is full ruggae disappears Stomach is lines with epithelial cells that contain gastric glands Cardiac glands Oxyntic glands o Contain no parietal cells but yes to the other cells o Neck mucus cells secrete bicarbonate and mucus o Parietal cells secrete HCL and intrinsic factor o Chief cells secrete pepsinogen o Enteroendocrine cells secrete hormones pyloric glands o mucus cells o parietal cells contain K Cl transport system and ATPase exchange system proton pump o Enteroendocrine G cells Gastric juice Water Electrolytes HCL secreted from gastric parietal cells o Pepsinogen pepsin o Denatures proteins opens interior bonds so pepsin can come in o Releases nutrients for organic complexes o Bactericide agent killing bacteria Enzymes o Pepsin made by chief cells and is the 1 protolytic enzyme in the stomach Autocatalytic It is an entopeptidase hydrolyzed interior peptide bonds within proteins o salivary amylase is inactivated by the low pH of stomach o gastric lipase made by chief cells hydrolyzes short and medium chain triglycerols Mucus secreted by neck cells coats lumen and lubricates food Intrinsic factor secreted by parietal cells necessary for Vit B12 absorption Hormones that inhibit gastric secretions Peptide YY Enterogastrone GIP VIP Substance powder P Secretin Somatostatin made by delta pancreatic and intestinal cells Nitric oxide Hormones that stimulate gastric secretions Gastric Releasing Peptide bombesin released from enteric nerves and stimulates gastrin and HCL release Gastrin made by Enteroendocrine G cells o Stimulate HCl release o Stimulate chief cells to release pepsinogen o Stimulates gastric motility and cellular growth of stomach o Release occurs in response to vagal stimulation distention HCl contact with gastric mucosa GRP epinephrine coffee alcohol Ca2 aa peptides Other way Acid release stimulated into stomach Vagus nerve releases acetylcholine and stimulates release of histamine Both acetylcholine and histamine stimulate acid secretion Gastrin stimulates histamine release o In sum Gastrin acts on parietal cells in stomach HCl gastrin HCl Acetylcholine released from vagus nerve to act on parietal cells Acetylcholine parietal cells HCl Histamine released from GIT mast cells to bind to Hydrogen receptors on parietal cells acetylcholine GRP gastrin HCL GERD because of reflux GES is weak and inappropriately relaxes Relieved by antacids Prevented by o H2 blockers pepsid AC block the binding site of H2 receptors o Proton pump inhibitors Prilosec nexium bind secretion site in cell and inhibit HCl secretion o Small intestine Chyme enters through the pyloric sphincter Duodenum jejunum ileum Structures that aid in the large surface area Fold of kerkring protrude into the lumen Villi fingerlike projections consists of hundred of enterocytes absorptive epithelial cells blood capillaries and a central lacteal for transport of nutrients out of enterocytes Microvilli hair like extensions of plasma membrane of the enterocytes that make up the villi intestines o Have a surface coat called glycocalyx lines the luminal side of the Made up of fine filaments that extends perpendicular to microvillus membrane o Together they make up the brush border Structurally digested enzymes are glycoproteins Digestion of nutrients is usually completed in the brush border Hormones that stimulate the release of intestinal secretions VIP relaxes GI sphincters Neuropep P motilin CCK o Motilin secreted by Enteroendocrine m cells stimulates gastric and duodenal motility gastric and pancreatic secretions and gall bladder contractions Hormones that inhibit the release of intestinal secretions Peptide YY Glucagon like peptides Secretin Digestion of proteins Hydrolysis to the tri and di peptides and amino acids via pancreatic protease Pancreatic proteases secreted from pancreas in its inactive form so they don t digest pancreas activated in lumen of duodenum Trypsinogen is converted to trypsin via entero peptidases Trypsin activates other
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