Physiology of the GIT PDF

Physiology of the GIT :By Department of Physiology- Suez University  Learning objectives List the parts of GIT and their-.functions Identify Structure of the digestive -.tract wall.Describe movements in GIT- Describe the process of mastication,-.swallowing List the source and fun...

Physiology of the GIT :By Department of Physiology- Suez University  Learning objectives List the parts of GIT and their-.functions Identify Structure of the digestive -.tract wall.Describe movements in GIT- Describe the process of mastication,-.swallowing List the source and functions of GIT-.secretions  Overview of the Digestive System The Digestive System :Consists of a)Long hollow muscular tube: Canal or tract called gastrointestinal tract or (GIT) It is about 5 meters long b) Accessory glands: :include Salivary glands Liver and gall bladder Pancreas ;GIT consists of Oral cavity or mouth Pharynx Esophagus Stomach Small intestine Large intestine Rectum Anus The wall of GIT Lumen of the GIT  Structure of the digestive tract wall: 1. The mucosa: lines the luminal surface. Its inner epithelial layer has exocrine and endocrine cells. 2. The submucosa: is under the mucosa. This connective tissue has large blood and lymph vessels. It contains a submucous plexus. 3. The muscularis externa: is the main smooth layer of the digestive tube. It has an inner circular layer and an outer longitudinal layer. A myenteric plexus is between the two smooth muscle layers. 4. Serosa: is the outer protective layer. 8  Regulation of GIT Functions Neural (nervous) Enteric nervous system-1 )local nerve plexuses( a-Meissner's plexus ( Submucosal nerve plexus) Control GIT Secretions. b-Auerbach's plexus ( Myenteric nerve plexus) Control GIT motility :Autonomic nerves-2.a-Sympathetic b-Parasympathetic (vagal, sacral) Hormonal They are all polypeptides secreted from special mucosal endocrine cells called APUD present throughout GIT, act on.GIT (other sites) local hormones =  Main Functions of Digestive Tract major activities of GI tract 4 Motility.1 Propel ingested food from.mouth toward rectum Secretion of juices e.g..2 saliva.Aid in digestion and absorption Digestion.3 Food broken down into.absorbable molecules 4.Absorption (Primary function) Nutrients, electrolytes, and water are absorbed or transported from lumen of GIT to blood stream.  GIT Motility :Electrical activity of GIT smooth muscles They are pacemaker cells (pace setter) in the GIT smooth -.muscles They are located between the longitudinal & circular Ms. -.layer These cells produce spontaneous depolarization and - repolarization in the form of slow waves which are called.Basic Electric Rhythm (BER) BER cannot reach the firing level to produce action-.potential Nerves and hormones stimulate these BER to reach the -.firing level and produce action potential Smooth ms cells which act as functional syncytium → - permit movement of ions between adjacent cells (gap junctions)  Motility of the GIT Motility in the mouth.1 :types 2 :a)Chewing or Mastication.Breaks the food into small pieces to be easily swallowed :b) Swallowing Swallowing is the transport of food from mouth to.stomach ;It consists of 3 phases or steps Buccal Phase: food is pushed back into pharynx from )1.mouth Pharyngeal Phase: food pass through pharynx to )2.esophagus Oesophageal Phase: food pass through esophagus to )3.stomach by peristaltic movements Motility of Esophagus.2 The esophagus is 25 cm muscular tube It is guarded by 2 :sphincters Upper esophageal sphincter.1 prevents air from entering the.GIT Lower esophageal.2 sphincter prevents gastric contents from re-entering the esophagus from.the stomach Esophageal peristalsis.sweeps down the esophagus  Motility of Stomach Proximal area (fundus and body) has a thin wall with weak contraction for storage of food due to receptive relaxation. Distal area (pylorus) has thick wall for peristalsis with strong contractions for mixing and emptying food to the duodenum. Motility of Small intestine.4 Two basic motility patterns exist (mixing).segmentation and peristalsis :Significance Segmentation Mixing contents with enzymes and other secretions →.1.help digestion Maximizing exposure of the contents to membranes of.2.intestinal cells → help absorption and digestion Peristalsis: Propulsion of contents into the large.intestine  Motility of Large intestine or colon : Include a) Haustration (mixing) in the large intestine causes the contents to be continuously.mixed b) Mass movement propels the contents of one segment of the large intestine into the next.downstream segment c) Defecation involves involuntary reflexes and voluntary Control→ evacuation of colonic content through anal.canal  Secretions of GIT The total volume of GIT secretions is about 6-8 L/day Secretions arise from specialized cells lining the GI.tract, the pancreas, liver and gallbladder GI secretions function to Lubricate (water and mucus) Protect (mucus) Sterilize (HCl) Neutralize (HCO3-) Digest (enzymes).  Secretions of GIT in Mouth Salivary Glands Three pairs of glands Parotid Sublingual Submandibular Gastric secretions :Functions of Gastric HCL Activates pepsinogen into pepsins.1 Provides optimum for pH for action of pepsins.2 Help digestion of protein.3 Kills bacteria in food.4.Help Fe2+ 、 Ca2+ absorption.5 Promotes pancreatic, small intestinal and bile.6 secretion :Function of Intrinsic Factor Help absorption of vitamin B12  Pancreatic Secretion :Pancreas has 2 functions a) Endocrine functions: secretes insulin and glucagon from islets. of Langerhans.b) Exocrine function: secretion of pancreatic juice.It has 2 components: aqueous and enzymatic components Aqueous component (contains HCO3) is important for neutralizing stomach.acid Enzymatic component is essential for the proper digestion and absorption of.carbohydrates, fats, and proteins.Pancreatic enzymes include trypsin, chemotrypsin, lipase, and amylase  Liver Functions of the Liver: 1) Metabolic regulation Store absorbed nutrients, vitamins. Release nutrients as needed. 2) Hematological regulation Plasma protein production. Remove old RBCs. 3) Production of bile 23  Gall bladder secretion :Functions of bile Importance of bile salts)1 Help in digestion of fat by emulsification of fats into small particles with more surface area exposed for.enzymatic action Bile salts combine with fatty acids, cholesterol& fat soluble. vitamins to form micelles (water soluble compounds)which can be easily absorbed from.intestinal villi Alkali content shares in neutralization of HCl in)2.duodenum.Its mucin content: lubricant & buffer)3  Gall Bladder Functions of the gall bladder: 1)Stores bile that help in fat digestion and absorption in intestine. 2)Concentrates bile. 3)Absorption of fat- soluble vitamins in the small intestine. 25 :Complete the following sentences ……Motility in the mouth are ……. And-1 Functions of saliva are ……., …….. And-2..…… Gastric HCL activates ………..into -3..…… Bile salts combine fat soluble vitamins-4..…… to form Pancreatic secretion contains ……. -5 Which is important for neutralizing stomach acid