Adult Medical- Surgical Nursing Gastro-intestinal System: Overview

Gastro-intestinal System: Overview  The GI system extends from the mouth to the rectum/ anus  Mouth: chewing and moistening, using teeth, tongue, saliva, swallowing, epiglottis  Salivary glands: parotid, sub-lingual, sub- mandibular:  Secrete ptyalin (salivary amylase), mucus and water

Gastro-intestinal System: Overview  Swallowing is a voluntary action regulated by the swallowing centre in the medulla oblongata (epiglottis covers the trachea)  Oesophagus: reflex peristaltic movement of bolus of food to the stomach  Stomach: cardiac sphincter, fundus, body, pyloric sphincter

Gastro-intestinal System: Overview  Digestion:  Gastric glands:  Parietal cells: secrete HCL (gastric pH 1-2)  Goblet cells: secrete mucus (protection)  Chief cells: secrete proteolytic enzyme, pepsin, and intrinsic factor  Gastric churning to form chyme, passed to duodenum via pyloric sphincter

Gastro-intestinal System: Overview  Duodenal wall glands secrete bicarbonate to neutralise acidity of the chyme  Pancreatic enzymes (alpha cells):  Trypsin (protein)  Amylase (CHO)  Lipase (fats)  Liver hepatocytes secrete bile: emulsifies fats

Gastro-intestinal System: Overview  Intestinal wall glands secrete mucus for protection from acidity and enzymes  Hormones controlling enzyme secretion:  Gastrin: by gastric antrum in presence of food → HCL secretion  Cholecystokinin: by gall bladder in response to fat in duodenum→ contraction of gall bladder to release bile  Secretin: by intestinal wall cells → secretion of bicarbonate

Gastro-intestinal System: Overview  Absorption:  Intestinal villi and micro-villi increase surface area for absorption of digested foods and minerals/ vitamins intact by:  Diffusion, osmosis and active transport  Absorption into portal vein → liver for metabolism (see lecture: “Functions of the Liver”)

Gastro-intestinal System: Overview  Excretion:  Four hours after eating food reaches the ileo-caecal valve → large intestine.  Water absorbed during passage to rectum/ anus