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Anatomy and physiology of GIT. Foregut Midgut Hindgut Coeliac artery Superior mesenteric artery Inferior mesenteric artery 5m Pharynx to duodenum Duodenum.

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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:

1 Anatomy and physiology of GIT

2 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

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4 Accessory digestive organs Teeth Tongue Salivary glands Liver Gallbladder Pancreas

5 Esophagus 25cm Pharynx Stomach A: L gastric artery (from celiac trunk) V: Portocaval anatomososes A: L gastric artery (from celiac trunk) V: Portocaval anatomososes Lymph: Lt gastric nodes Drain mainly to celiac lymph nodes Lymph: Lt gastric nodes Drain mainly to celiac lymph nodes Nerve: Ant + post gastric nerves (vagi), sympathetic branches of thoracic trunk. Internal circular and external longitudinal layers of muscle 1/3: voluntary 1/3: mix 1/3: smooth muscle stratified squamous non-keratinized epithelium

6 Function: Oral cavity and esophagus Mechanical: Chew  swallow  peristalsis to stomach Secretion: Saliva (lysozyme, defensins, and IgA ab), amylase, lipase Digestion: Carbohydrates and fat (minimal) Absorption: None

7 Fundus Greater curvature Lesser curvature Body Antrum Pylorus Cardiac orifice Lt of midline, T11 Rt of midline, L1 (Transpyloric plane) Can hold up to 2-3L Simple columnar Covered by mucous layer

8 Lymph: follows arteries  celiac nodes Nerves: Celiac plexus – both sympathetic and parasympathetic Celiac trunk Portal vein Pain – poorly localised Referred – gastric ulcer – T7,T8 sensory ganglia

9 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

10 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)

11 Coeliac art Sup mesenteric art Through mesentry, forming arcades Lymph: Coeliac + Sup mesenteric nodes Nerve: Coeliac + sup mesenteric plexus

12 Small intestine epithelium Villi covered by simple columnar epithelium Intestinal glands Enterocytes (absorptive cell) Goblet cells: mucus secreting Paneth cells: regulate intestinal flora Enteroendocrine cells: CCK, secretin (bicarb), GIP (gastric inhibitory peptide- inhibits gastric acid)

13 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

14 sup mesenteric nodes. Sup mesenteric nerve plexus inf mesenteric nodes. Inf mesenteric plexus: Sympathetic (lumbar splanchnic nerves) Parasympathetic S2-S4 Inf mesenteric plexus: Sympathetic (lumbar splanchnic nerves) Parasympathetic S2-S4

15 Function: Large intestine M: Segmental mixing; propulsion – mass movement. S: mucus by goblet cells. D: None. A: Ions, water, minerals, vitamins produced by bacteria.

16 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.

17 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.

18 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.

19 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).

20 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.


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