Presentation on theme: "Anatomy and physiology of GIT. Foregut Midgut Hindgut Coeliac artery Superior mesenteric artery Inferior mesenteric artery 5m Pharynx to duodenum Duodenum."— Presentation transcript:
Anatomy and physiology of GIT
Foregut Midgut Hindgut Coeliac artery Superior mesenteric artery Inferior mesenteric artery 5m Pharynx to duodenum Duodenum to first 2/3 of transverse colon Last 1/3 of transverse colon to upper half of anal canal
Glands The stomach is divided into three histological regions based on the nature of the glands. Cardiac region: near the opening of the oesophagus. Mucus-secreting cells. Protects the oesophagus against gastric reflux. Fundic region: long glands, narrow neck and a short, wider base. – Cell types found – Mucous neck cells – Parietal (oxyntic) cells: HCL and intrinsic factor (B12). – Chief cells: pepsinogen and a weak lipase – Enteroendocrine cells: more prevalent near the base. Secrete products into lamina propria where it is taken up by blood vessels. Secretes gastrin – stimulates production of HCL. Pyloric region: mucous
Function: Stomach Mechanical: mixing and propulsion Secretion: – Parietal cells: HCl – Chief cells: Pepsinogen and lipase – Surface mucus cells: Mucus and HCO -3 – G cells: Gastrin – ECL cells: Histamine Digestion: Proteins and fats Absorption: Lipid soluble (alcohol, aspirin etc)
Coeliac art Sup mesenteric art Through mesentry, forming arcades Lymph: Coeliac + Sup mesenteric nodes Nerve: Coeliac + sup mesenteric plexus
Function: Small intestine M: Mixing – enzymes from pancreas and liver; propulsion – segmentation. S: – Goblet cells: Mucus – Hormones: CCK, Secretin, GIP D: Carbohydrates, fats, protein and nucleic acids. A: Peptides by active transport; amino acids, glucose and fructose by secondary active transport; fats by simple diffusion; water by osmosis; ions, minerals and vitamins by active transport
Function: Large intestine M: Segmental mixing; propulsion – mass movement. S: mucus by goblet cells. D: None. A: Ions, water, minerals, vitamins produced by bacteria.
Physiology of absorption: Carbohydrate Glucose rapidly absorbed before terminal part of ileum. Transport affected by Na + in intestinal lumen sodium-dependent glucose cotransporter. – Secondary active transport – Congenital defective – glucose/galactose malabsorption (severe diarrhoea) Fructose different mech, independent of Na +. Insulin little effect on sugar absorption in intestine not depressed during DM.
Physiology of absorption: Protein 7 diff syst for amino acids: 3 Na + dependent, 2 Na + & Cl - dependent. Di/tripeptides H + dependent. Hartnup disease: defect in AA absorption from intestine and tubules in the kidneys. Cystinuria: inadequate reabsorption of cystine in PCT of kidneys. Infants: undigested proteins absorbed maternal IgA by transcytosis. – Adults: causes allergies. Absorption of antigen by microfold (M) cells transport to Peyer’s patches, lymphocytes activated.
Physiology of absorption: Lipid Passive diffusion esterified. Uptake of bile salts by jejunal mucosa low form new micelles. Process not fully matured in infants fail to absorb 10-15% of ingested fat. – More susceptible to fat malabsorption diseases. Cholesterol: needs bile, fatty acids and pancreatic juice. – Sterols of plant origin poorly absorbed compete with cholesterol and reduce cholesterol absorption.
Physiology of absorption: water and electrolytes. 98% of fluid reabsorbed,~200mL excreted in stool. – Mainly in small and large intestine. Na + diffuses across small intestine through gradient; basolateral surface has Na + -K + ATPase actively absorbed. Cl - enterocytes via Na + -K + -2Cl - cotransporters secreted via channels. – Cholera bacillus: increased Cl - secretion, reduced Na + absorption. Glucose / cereal containing carbs (tx of diarrhoea).
Jejunum – osmolality of content close to that of plasma absorption of osmotically active particles. Saline cathartics (Mg 2+ sulfates) poorly absorbed salts, increase intestinal volume laxatives. K + secreted into intestinal lumen as mucus. H + - K + ATPase in distal colon reabsorbs. – Loss of ileal or colonic fluid (diarrhoea) can lead to severe hypokalaemia. Physiology of absorption: water and electrolytes.