Chapter56 (2).pdf

Chapter 56 Introduction to the Gastrointestinal System Copyright Copyright © 2017 © 2012 Wolters Wolters Kluwer Kluwer All Health Rights Reserved...

Chapter 56 Introduction to the Gastrointestinal System Copyright Copyright © 2017 © 2012 Wolters Wolters Kluwer Kluwer All Health Rights Reserved | Lippincott Williams & Wilkins The Gastrointestinal Tract Copyright © 2023 Wolters Kluwer All Rights Reserved Structures of the GI System Tube that comprises GI tract continuous with external environment, opening at mouth and again at anus Progresses through the esophagus, stomach, and small and large intestines Accessory Organs o Pancreas o Liver o Gallbladder Copyright © 2023 Wolters Kluwer All Rights Reserved Layers of the GI Tract Mucosal layer Submucosal layer Muscularis external layer Serosal layer Enteric nervous system o Sympathetic and parasympathetic influence on GI tract Copyright © 2023 Wolters Kluwer All Rights Reserved GI Tract Copyright © 2023 Wolters Kluwer All Rights Reserved Major Activities of the GI System Secretion of enzymes, acid, bicarbonate, and mucus Digestion of food into usable and absorbable components Absorption of water and almost all of the essential nutrients needed by the body Motility of food and secretions through the system Copyright © 2023 Wolters Kluwer All Rights Reserved Compounds Secreted in the GI Tract  Saliva  Mucus  Acid and digestive enzymes o Gastrin o Hydrochloric acid  Ghrelin  Secretin  Sodium bicarbonate  Pancreatic enzymes, lipases, and amylases  Bile  Endocrine hormones Copyright © 2023 Wolters Kluwer All Rights Reserved Question #1 Please answer the following statement as true or false. Ghrelin breaks apart fat molecules so they can be processed and absorbed. Copyright © 2023 Wolters Kluwer All Rights Reserved Answer to Question #1 False Rationale: Ghrelin is thought to prepare the body for digestion of a meal and to stimulate more secretion of growth hormone. Bile contains a detergentlike substance that breaks apart fat molecules. Copyright © 2023 Wolters Kluwer All Rights Reserved Digestion Process of breaking food into usable, absorbable nutrients Begins in the mouth with enzymes in the salvia Stomach continues the digestion process o Muscular churning o Acid and enzymes In small intestine, bile breaks down fat molecules Copyright © 2023 Wolters Kluwer All Rights Reserved Absorption Active process of removing water, nutrients, and other elements from the GI tract and delivering them to the bloodstream for use in the body. Portal system drains all of lower GI tract; delivers what is absorbed into the venous system directly to the liver. Liver filters, clears, and further processes most of what is absorbed before delivery to body. Most absorption occurs in small intestine. Copyright © 2023 Wolters Kluwer All Rights Reserved Motility  GI tract depends on an inherent motility to keep things moving through the system.  Nerve plexus maintains BER.  Basic movement in esophagus is peristalsis.  Stomach uses its three muscle layers to produce churning action.  Small intestine uses process of segmentation with occasional peristaltic wave.  Large intestine uses process of mass movement with occasional peristaltic wave.  Rectal distention after mass movement stimulates defecation reflex. Copyright © 2023 Wolters Kluwer All Rights Reserved Local Gastrointestinal Reflexes  Gastroenteric reflex o Stimulation of the stomach by stretching, presence of food, or cephalic stimulation o Causes increase in activity in small intestine  Gastrocolic reflex o Stimulation of the stomach o Causes increased activity in the colon  Duodenal–colic reflex o Triggered by presence of food or stretch in the duodenum o Stimulates colon activity and mass movement Copyright © 2023 Wolters Kluwer All Rights Reserved Other Local GI Reflexes Ileogastric reflex Intestinal–intestinal reflex Peritoneointestinal reflex Renointestinal reflex Vesicointestinal reflex Somatointestinal reflex Copyright © 2023 Wolters Kluwer All Rights Reserved Central Reflexes  Swallowing reflex o Stimulated when a food bolus stimulates pressure receptors in the back of the throat and pharynx o Medulla stimulates series of nerves to cause actions for swallowing  Vomiting reflex o Protects the system from unwanted irritants o Stimulated by two centers in the medulla  Emetic zone  Chemoreceptor trigger zone Copyright © 2023 Wolters Kluwer All Rights Reserved Stimulation of the CTZ Tactile stimulation of the back of the throat Excessive stomach distention Increasing intracranial pressure by direct stimulation Stimulation of the vestibular receptors in the inner ear Stimulation of stretch receptors in the uterus and bladder Intense pain fiber stimulation Direct stimulation by various chemicals Copyright © 2023 Wolters Kluwer All Rights Reserved Question #2 Please answer the following statement as true or false. When the renal capsule becomes irritated, the gastrointestinal tract shuts down. Copyright © 2023 Wolters Kluwer All Rights Reserved Answer to Question #2 True Rationale: With the renointestinal reflex, irritation or swelling of the renal capsule causes a cessation of movement in the GI tract, preventing further irritation to the capsule. Copyright © 2023 Wolters Kluwer All Rights Reserved