Anatomy and physiology of GIT
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Transcript of Anatomy and physiology of GIT
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
Accessory digestive organs
• Teeth• Tongue• Salivary glands• Liver• Gallbladder• Pancreas
Esophagus
25cm
Pharynx
Stomach
A: L gastric artery (from celiac trunk)V: Portocaval anatomososes
Lymph: Lt gastric nodesDrain mainly to celiac lymph nodes
Nerve: Ant + post gastric nerves (vagi) , sympathetic branches of thoracic trunk.
Internal circular and external longitudinal layers of muscle1/3: voluntary1/3: mix1/3: smooth muscle
stratified squamous non-keratinized epithelium
Function: Oral cavity and esophagus
• Mechanical: Chew swallow peristalsis to stomach
• Secretion: Saliva (lysozyme, defensins, andIgA ab), amylase, lipase
• Digestion: Carbohydrates and fat (minimal)• Absorption: None
Fundus
Greater curvature
Lesser curvature
Body
AntrumPylorus
Cardiac orifice
Lt of midline, T11
Rt of midline, L1 (Transpyloric plane) Can hold up to
2-3L
Simple columnarCovered by mucous layer
Lymph: follows arteries celiac nodes
Nerves: Celiac plexus – both sympathetic and parasympathetic
Celiac trunk
Portal vein
Pain – poorly localisedReferred – gastric ulcer – T7,T8 sensory ganglia
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
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)
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
sup mesenteric nodes.
Sup mesenteric nerve plexus
inf mesenteric nodes.
Inf mesenteric plexus:Sympathetic (lumbar splanchnic nerves)Parasympathetic S2-S4
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 (Mg2+ 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.