Digestive System: Gastrointestinal Tract Anatomy

DIGESTIVE SYSTEM By : Dr. Omer  Regulation of the GI Tract  Enteric nervous system:  Autonomic nervous system.  Hormonal secretion: Secreted by the mucosa. Enteric nervous system  The digestive system consists of: Gastrointestinal tract Accessory digestive organs T...

DIGESTIVE SYSTEM By : Dr. Omer  Regulation of the GI Tract  Enteric nervous system:  Autonomic nervous system.  Hormonal secretion: Secreted by the mucosa. Enteric nervous system  The digestive system consists of: Gastrointestinal tract Accessory digestive organs The gastrointestinal tract (GIT)is essentially a tube that runs from the mouth to the anus. This tube consists of the following organs: Mouth Pharynx Esophagus Stomach Small intestine Large intestine The accessory digestive organs exist outside the gastrointestinal tract; however, each of these organs empties secretions into the tract that contribute to the process of digestion. These accessory digestive organs include:  Salivary glands  Liver  Gallbladder  Pancreas  The mouth  Functions:-  Mastication.  Mixes food with saliva.  Initiates swallowing.  Swallowing (Deglutition)  Is the process by which the food pass from the mouth to the stomach through the esophagus.  It occurs 3 phases :- 1.Oral (voluntary) phase 2.Pharyngeal (involuntary) phase 3.Esophageal (involuntary) phase  Phases of swallowing 1. Oral phase 2. Pharyngeal phase 3. Esophageal phase.  Normal Swallowing and Choking Tongue Food Larynx rises Esophagus (to stomach) Epiglottis closes Trachea (to lungs) over larynx  SWALLOWING DISORDERS  Dysphagia:-refers to difficulty in swallowing  Achalasia : failure of lower esophageal sphincter to relax.  Gastro esophageal reflux disease:  The condition in which the gastric acid content reflux back in to the esophagus. Cause heart burn. Salivation  Saliva:-  Fluid in the mouth produced by salivary glands.  The salivary glands include:  The submandibular gland: secretes 70% of saliva.  The parotid glands: secretes 25% of saliva.  The sublingual gland: secretes 5% of saliva.  Characteristics of saliva  Volume: 1.5 L/day.  Osmolarity: hypotonic.  pH: alkaline.  Contents: I. Water & ions. II. mucous, antibodies(A) & lysozymes. III. Digestive enzymes: alpha amylase for digestion of starch & lingual lipase for digestion of lipids.  Functions of the saliva  Protection: by lysozyme & antibodies.  Digestion: by alpha amylase & lingual lipase.  Lubrication to facilitate: swallowing, speech & taste.  Buffer: neutralizes acids regurgitated form stomach.   Parasympathetic stimulation (the dominant role) produces a prompt and abundant flow of watery saliva that is rich in enzymes.  Sympathetic stimulation produces a smaller volume of thick saliva that is rich in mucus.. Click icon to add picture Gastric secretion Functions of the stomach  Stores food up to about 4 hours, and controls its release into the duodenum.  Digestion of proteins(start in the stomach) & lipids.  Protection by HCL.  HCL also activate the pepsinogen and maintains iron in the ferrous state to facilitate its absorption.  Production of intrinsic factor to facilitate absorption of vitamin B12  Hormonal function: produces the  The mucosa of the stomach contains many exocrine glands (gastric glands).  Types of cells in a gastric glands:  Mucous cells: secretes mucous.  Parietal cells: secretes HCL & intrinsic factor.  Chief cells: secretes pepsin enzyme for protein digestion.  Gastric juice  Features of the gastric juice:-  Volume: 2-3 L/day.  pH: highly acidic.  Osmolarity: isotonic  Contents:  Water & ions (H+/CL…..)  Intrinsic factor  Digestive enzymes Types of cells and their secretion Gastric secretions Regulation  Parietal cells secrete acid in response to three types of stimuli: 1. Histamine stimulates H2 histamine receptors (most significant contribution). 2. Acetylcholine, from parasympathetic activity via the vagus nerve, stimulating M3 receptors 3. Gastrin, stimulating CCK receptors (least significant contribution, but also causes histamine secretion by local ECL cells)  Gastric mucosal barrier  It has two layers:  Outer layer: mucous.  Inner layer: HCO3.  Function :  It protects the gastric mucosa from action of gastric acid and pepsin.