![- Midgut: to ⅔rd transverse colon,
superior mesenteric artery, lesser
splanchnic nerve
- Hindgut: to dentate line (rectum),
inferior mesenteric artery, least
splanchnic nerve
!
Stomach
- Anterior: diaphragm, transverse colon,
liver
- Posterior: pancreas, spleen, kidney
- Supply: right & left gastric,
gastroepiploic, short gastric [splenic
runs posterior]
- Drain to splenic and superior
mesenteric veins
- Extra (external) oblique muscle layer
- Functions:
- Store & regulate release
- Protein & vit B12 digestion
- Immune defence
- Cephalo-gastric and gastro-gastric
reflexes inhibit vagal contraction to
fill without pressure rise
- Rugae also help filling
without pressure increase
Ⓒ One 2 One Medicine: Pre-clinical revision course 2014 Page ! of !5 20
GIT embryology
Stomach anatomy
Coeliac axis
branches
EXAMPLE](https://image.slidesharecdn.com/digestive-system-sample289-160126092042/85/Digestive-System-Sample-2-320.jpg)
Digestive System Sample
- 1. Stomach ! Abdominal anatomy - Abdomen: diaphragm to pelvic brim - Antero-lateral muscular wall: external oblique, internal oblique, transversus abdominus - Posterior: quadratus lumborum, psoas, spine - Anterior wall supply: - External iliac → inferior epigastric → superior epigastric → internal thoracic → subclavian - Peritoneum = single-cell layer that covers organs and inner of anterior abdominal wall - If visceral peritoneum only on anterior = retroperitoneal - Mesentery = double-layer of peritoneum - Connects small bowel to posterior wall and carries vessels - Greater sac divided by the transverse mesocolon - Behind gastro-hepatic ligament = lesser sac - Contains gastro-epiploic foramen (of Winslow) that connects sacs - Omentum connects stomach to other organs - Lesser - liver - Greater - transverse colon - Foregut: mid-oesophagus to ampulla of Vater, coeliac trunk, greater splanchnic nerve Ⓒ One 2 One Medicine: Pre-clinical revision course 2014 Page ! of !4 20 Peritoneum and associated structures Abdominal wall blood supply External iliac Inferior epigastric Superior epigastric Internal thoracic EXAMPLE
- 2. - Midgut: to ⅔rd transverse colon, superior mesenteric artery, lesser splanchnic nerve - Hindgut: to dentate line (rectum), inferior mesenteric artery, least splanchnic nerve ! Stomach - Anterior: diaphragm, transverse colon, liver - Posterior: pancreas, spleen, kidney - Supply: right & left gastric, gastroepiploic, short gastric [splenic runs posterior] - Drain to splenic and superior mesenteric veins - Extra (external) oblique muscle layer - Functions: - Store & regulate release - Protein & vit B12 digestion - Immune defence - Cephalo-gastric and gastro-gastric reflexes inhibit vagal contraction to fill without pressure rise - Rugae also help filling without pressure increase Ⓒ One 2 One Medicine: Pre-clinical revision course 2014 Page ! of !5 20 GIT embryology Stomach anatomy Coeliac axis branches EXAMPLE
- 3. Lower oesophageal sphincter - Competent if sphincter pressure exceeds gastric pressure, contributing factors: - Muscular (physiological) sphincter itself - Increase in intra-abdominal/-thoracic pressure with coughing, talking, exhalation - Acute angle between oesophagus & stomach with mucosal flaps - Gravity relatively minor role - Gastro-oesophageal reflux disease (GORD): pain, cough, regurgitation - Chronic oesophagitis may give Barrett's metaplasia (to gastric type) - Increased cancer risk Gastric physiology - Parietal cells secrete H+ via proton pump (H+- ATPase) made by carbonic anhydrase (on H2O) + CO2) - Target for proton pump inhibitors (e.g. omeprazole) - Basolateral HCO3 - excretion (for Cl-) makes alkaline tide - Control: - Vagal innervation of parietal cells increases directly - Indirectly: via gastrin from G-cells and binds CCKB-receptor on parietal cells - Gastrin reduced by secretin (from duodenal S-cells in response to acid) - Histamine (ECL cells) increases acid production at H2-R on parietal cells - Target for histamine antagonists (e.g. ranitidine) - Somatostatin inhibits directly on parietal cells - Indirectly: via reducing histamine production from ECL cells - Mucus increased by ACh (therefore at same time as acid) using PGE2 - Use of NSAIDs reduce PG production and predisposes to gastritis/ulcers Ⓒ One 2 One Medicine: Pre-clinical revision course 2014 Page ! of !6 20 Gastric acid secretion Cell type Secretions Function Parietal cells Gastric acid and intrinsic factor Denature protein, immune protection, pepsinogen activation Chief cells Pepsinogen Protein digestion APUD (amine precursor uptake decarboxylase) cells Somatostatin Inhibit acid and increase mucus production G-cells Gastrin Increase acid production Mucus-secreting cells Alkaline mucus Protect epithelium from acid-damage ECL (entero- chromaffin-like) cells Histamine Increase acid production EXAMPLE
- 4. - Gastric motility - Mixing in corpus - Propulsion moves towards antrum - Retropulsion back from antrum/pylorus to corpus - Pylorus relaxes in response to: distention, small boluses, peptides ! Small bowel ! Anatomy - Duodenum: superior (coeliac) & inferior (SMA) pancreato-duodenal arteries - Posterior to 1st: common bile duct, gastroduodenal artery and portal vein - Posterior to 2nd: right kidney and ureter - 3rd: around head of pancreas, crossed by root of the mesentery & SMA - 4th: ligament of Trietz at duodeno-jejunal junction with IMV to left - Histology: - Brunner's glands: deep, alkaline-secreting, only in duodenum Ⓒ One 2 One Medicine: Pre-clinical revision course 2014 Page ! of !7 20 Helicobacter pylori - Bacterium specialised to living in stomach - Associated with peptic ulcer disease - Urease produces an alkaline coat - Flagella to bury into mucus - Inhibits somatostatin secretion → increases acid Control of gastric acid Duodenal anatomy EXAMPLE
- 5. - Simple columnar with microvilli - Jejunum (2/5th): thicker with smaller lumen - Plicae circulares (/valvulae conniventes) = folds in small bowel - Villae (= mucosae) with crypts of Leiberkuhn at base (new cells produced at base) - Peyer's patches = lymphoid aggregates - B-cells make secretory IgA that prevent pathogen adhesion - Panneth cells secrete lysozyme ! ! ! ! ! ! ! ! ! ! Absorption ! Water & ions - Basolateral Na+/K+-ATPase gives concentration gradient for apical facilitated diffusion: co-transport with glucose, amino acids and chloride - Water via osmosis through leaky occluding junctions in upper GIT and small bowel - Large bowel through aquaporins and transcellular movement - More controlled - K+ and Cl- move by paracellular transport; plus H+/K+-ATPase absorbs K+ in colon ! Ca2+ - Facilitated uptake in duodenum - binds calbindin inside cells (keeps gradient) - Basolateral efflux by Ca2+-ATPase or Na+/Ca2+-antiporter - PTH increases channel activity and vitamin D increases calbindin synthesis ! Ⓒ One 2 One Medicine: Pre-clinical revision course 2014 Page ! of !8 20 - Peritoneal cavity has a greater and lesser sac, separated by the stomach and it’s attachments - Mesentery is double-layered peritoneum containing neurovascular supply - Gastric parietal cells produce acid using H+/K+-ATPase - Duodenum is retroperitoneal and is both fore- & mid-gut Sodium & water absorption in the small bowel EXAMPLE