GI Tract Intro Lecture Student View PDF

Gastrointestinal physiology 1 Secretions of the gastrointestinal tract and their regulation David Simcock  Objectives Describe the secretions of the gastrointestinal tract Describe motility in the gastrointestinal tract Examine the digestion of protei...

Gastrointestinal physiology 1 Secretions of the gastrointestinal tract and their regulation David Simcock  Objectives Describe the secretions of the gastrointestinal tract Describe motility in the gastrointestinal tract Examine the digestion of proteins, carbohydrates and lipids in: – Mouth – Stomach – Small intestine Describe nutrient metabolism in the absorptive state  The mouth Salivation Parotid – Serous (hydrate) Sublingual – Mucus (lubricate) Submandibular – Serous (hydrate)  The mouth Lubrication/hydration of food Digestive enzymes – Lingual lipase – Lingual (salivary) amylase – Lysozyme  Gastric digestion Gastric glands secrete – Acid – Pepsinogen – Lipase – Mucus  The small intestine – acid neutralisation Digestion phase – the duodenum Relatively steady flow from stomach 1. Neutralise the chyme Brunner’s glands pancreatic secretions Gall bladder secretion  Motility - the mouth Swallowing (deglutition) Epiglottis closes Bolus pushed back Oropharynx relaxes Peristalsis  The oesophagus Propel food to the stomach Upper third skeletal muscle Lower two thirds smooth muscle Circular and longitudinal muscle contract Peristaltic waves Bidirectional  Secretions -summary Mouth secretes Stomach secretes Small intestines secrete  Primary peristalsis Starts at pharynx Involves skeletal muscle – Regulated by vagus Circular muscle – Relaxes then contracts Longitudinal muscle contracts  Secondary Peristalsis Muscle starts relaxed Bolus of digesta causes stretch Stretch causes contraction Can be reversed!  The stomach Muscular contractions and mixing Cardiac sphincter Pyloric sphincter  Motility in the stomach LOS should remain shut Pylorus regulates flow Churning – Peristalsis, but pylorus shut Emptying – Peristalsis but pylorus open  Motility summary Autonomic motility starts in Is called Involves contractions of Involves relaxation of  Digestion - prior to the intestine… Digestion prior to the intestine – Carbohydrates – Proteins – Lipids Flow of materials – how is a slow, constant flow of materials to the intestine developed after a large meal?  The small intestine - digestion Digestion duodenum Proteins – Trypsin – Chymotrypsin – Elastase – Carboxypeptidases – Aminopeptidases – Aminopeptidase on brush border of enterocytes, others from pancreas  The small intestine - digestion Digestion phase duodenum - release enzymes Carbohydrates – Amylase – Dextrinase – Glucolyase – Lactase Brush border Make (of epithelium) – Maltase monosaccharides – Isomaltase For absorption – Sucrase  The small intestine - digestion Digestion phase – duodenum release enzymes + bile Lipids – Lipase – Bile salts – Bile acids – Droplet formation  Summary – digestion Which enzymes are involved in protein digestion and where are these secreted from? Which enzymes are involved in carbohydrate digestion and where are these located/secreted from? What is secreted to aid lipid digestion and where do these secretions arise from?  Absorption - Proteins – duodenum and jejunum Di and tri peptides Amino acids Active transporters apical Passive transporters basolateral  Absorption - carbohydrates Duodenum –jejunum monosaccharides Active transport apical Passive transport basolateral  Absorption lipids Duodenum – jejunum + ileum Lipid droplets absorbed by endocytosis Lipids digested further packaged into chylomicrons Lacteals transport chylomicrons  Absorption – water and electrolytes Jejunum – ileum 90% of GI reabsorption Passive (ion gradient) intranet.tdmu.edu.ua