Stomach and small intestine
Stomach, Duodenum and Small Intestine: Anatomy, Blood Supply and Surgery
Stomach, duodenum, jejunum and ileum for FCPS Part 1: relations, blood supply, vagal nerves, duodenal parts and small bowel features. Covers ulcer bleeding, vagotomy, dumping, resection effects and Meckel's diverticulum.
One of the most tested topics in past papers
Stomach: parts, relations and secretions
- Parts: cardia, fundus, body, antrum, pylorus. The pylorus lies on the transpyloric plane (L1), just right of the midline.
- Stomach bed (behind the lesser sac): pancreas, splenic artery, left kidney and adrenal, spleen, transverse mesocolon, left crus of diaphragm.
| Region | Main cells | Product |
|---|---|---|
| Fundus and body | Parietal (oxyntic) cells | HCl and intrinsic factor |
| Fundus and body | Chief cells | Pepsinogen, gastric lipase |
| Antrum | G cells | Gastrin |
| Throughout | Surface mucous cells; D cells | Mucus and bicarbonate; somatostatin |
- Gastric emptying is slowed by fat and acid entering the duodenum, through CCK, secretin and GIP, and by the enterogastric reflex; it is promoted by gastric distension, gastrin and motilin. Liquids leave faster than solids.
Stomach: blood supply and why it resists ischaemia
| Vessel | From | Runs along |
|---|---|---|
| Left gastric | Coeliac trunk | Lesser curvature, upper part; oesophageal branches |
| Right gastric | Hepatic artery proper | Lesser curvature, lower part |
| Right gastroepiploic | Gastroduodenal (from common hepatic) | Greater curvature |
| Left gastroepiploic | Splenic | Greater curvature |
| Short gastrics | Splenic | Fundus, via gastrosplenic ligament |
- Arcades along both curvatures anastomose freely with each other and with a dense submucosal plexus, so ligating one or two named arteries rarely causes gastric necrosis. This is why the stomach can be pulled up as a conduit on the right gastroepiploic artery alone; its fundal tip is the part most at risk.
- Ulcer bleeding follows the nearest artery: lesser curvature ulcer erodes the left gastric; posterior gastric wall ulcer can erode the splenic artery.
- Lymph follows the arteries to coeliac nodes; spread to the left supraclavicular node (Virchow's) is a sign of advanced gastric cancer.
Vagal supply and vagotomy
- Anterior vagal trunk (mainly left vagus) and posterior trunk (mainly right) enter with the oesophagus. Each gives a nerve of Latarjet along the lesser curvature ending in a "crow's foot" to the antrum and pylorus. The anterior trunk sends a hepatic branch; the posterior a coeliac branch.
- Vagus drives acid secretion (acetylcholine on parietal cells, gastrin release) and relaxes the pylorus to allow emptying.
| Operation | Divides | Consequence |
|---|---|---|
| Truncal vagotomy | Both trunks at the hiatus | Pylorus no longer relaxes: gastric stasis, early satiety, vomiting of undigested food; needs a drainage procedure (pyloroplasty or gastrojejunostomy); post-vagotomy diarrhoea |
| Highly selective vagotomy | Branches to fundus and body only | Crow's foot kept, emptying normal; no drainage needed |
- The criminal nerve of Grassi is an early branch of the posterior trunk running behind the oesophagus to the fundus. If missed, acid secretion persists and the ulcer recurs. Always exclude gastrinoma (check fasting gastrin) in recurrent ulcer.
After gastric surgery: dumping
| Type | Timing | Mechanism | Features |
|---|---|---|---|
| Early dumping | 10–30 min after a meal | Hyperosmolar food enters the jejunum; fluid shifts into the lumen; vasoactive peptides | Bloating, cramps, palpitations, faintness, diarrhoea |
| Late dumping | 1–3 hours after a meal | Rapid glucose absorption causes hyperglycaemia and an excessive insulin surge | Reactive hypoglycaemia: sweating, tremor, confusion |
Pyloric stenosis
- Infantile hypertrophic pyloric stenosis: hypertrophy of the circular muscle of the pylorus; first-born boys, 2–8 weeks.
- Non-bilious projectile vomiting (obstruction is above the ampulla), hungry after feeds, olive-shaped mass in the right upper quadrant during a test feed; hypochloraemic hypokalaemic metabolic alkalosis.
Duodenum
About 25 cm, C-shaped around the head of the pancreas; the first 2 cm (duodenal cap) is intraperitoneal, the rest retroperitoneal.
| Part | Level | Key relations |
|---|---|---|
| First (superior) | L1 | Gastroduodenal artery and CBD behind; epiploic foramen above |
| Second (descending) | L1–L3 | Major papilla on posteromedial wall about 8–10 cm from pylorus; right kidney behind; gallbladder in front |
| Third (horizontal) | L3 | Crossed in front by SMA and SMV; aorta and IVC behind |
| Fourth (ascending) | L2 | Ends at DJ flexure, held by the suspensory ligament of Treitz |
- Posterior duodenal ulcer erodes the gastroduodenal artery: major haematemesis or melaena. Anterior duodenal ulcer perforates into the greater sac: free gas under the diaphragm; fluid may run down the right paracolic gutter to the right iliac fossa.
- Brunner's glands in the duodenal submucosa secrete alkaline mucus that neutralises acid; they are a duodenal identifying feature.
- Kocher manoeuvre: incise the peritoneum lateral to D2 and sweep the duodenum and pancreatic head medially, exposing the IVC behind.
- Retroperitoneal duodenal rupture (handlebar or seat-belt blow, often at the D2–D3 junction crushed against the spine): initially well, then back pain, vomiting and fever; CT shows gas around the right kidney with no free intraperitoneal gas.
- SMA syndrome: D3 compressed between aorta and SMA after rapid weight loss. Duodenal atresia (Down syndrome) gives a double bubble.
- The papilla marks the foregut–midgut junction: superior pancreaticoduodenal (coeliac) above, inferior pancreaticoduodenal (SMA) below. The ligament of Treitz separates upper from lower GI bleeding.
Jejunum versus ileum
| Feature | Jejunum | Ileum |
|---|---|---|
| Position | Upper left | Lower right, pelvis |
| Wall and lumen | Thicker, wider | Thinner, narrower |
| Plicae circulares (valvulae conniventes) | Tall, closely packed | Few, low; terminal ileum nearly smooth |
| Vasa recta | Long, one or two arcades | Short, many arcades |
| Mesenteric fat | Less; translucent windows | More fat to the bowel wall |
| Lymphoid tissue | Scattered | Peyer's patches |
| Absorbs | Most nutrients, folate; iron in duodenum | Vitamin B12 and bile salts |
- On X-ray, dilated jejunum shows plicae crossing the full width of the loop ("stack of coins"); colon shows haustra that cross only part of the width.
What resection removes
- Jejunal resection: the ileum adapts; folate deficiency is possible (macrocytic anaemia with normal B12).
- Terminal ileal resection (Crohn disease): B12 deficiency, bile salt loss, steatorrhoea. With the colon intact, unabsorbed fatty acids bind calcium, leaving oxalate free to be absorbed in the colon: enteric hyperoxaluria and calcium oxalate stones.
- Ileostomy (no colon): loss of water and bicarbonate gives concentrated, acidic urine, favouring uric acid stones (radiolucent on X-ray, seen on CT).
- Gallstone ileus: a large stone erodes through a cholecystoduodenal fistula, impacts at the narrow terminal ileum; pneumobilia, small bowel obstruction and an ectopic stone (Rigler's triad). It is mechanical obstruction, not true ileus.
Meckel's diverticulum
- Persistent vitellointestinal (omphalomesenteric) duct; a true diverticulum on the antimesenteric border.
- Rule of 2s: about 2% of people, 2 feet (60 cm) from the ileocaecal valve, 2 inches long, symptoms often before age 2, two ectopic tissues (gastric, pancreatic).
- Acid from ectopic gastric mucosa ulcerates adjacent ileum: painless rectal bleeding in a child; diagnosed by technetium-99m pertechnetate scan. May also cause intussusception, volvulus around a fibrous band, Littre's hernia or diverticulitis mimicking appendicitis.
Remember Posterior duodenal ulcer bleeds from the gastroduodenal artery; anterior duodenal ulcer perforates.
Exam trap Folate is lost with jejunal resection, B12 with terminal ileal resection; hypersegmented neutrophils occur in both.
Exam trap Oxalate stones need an intact colon; an ileostomy favours uric acid stones.
How FCPS asks about this
- Bleeding posterior duodenal ulcer: gastroduodenal artery; lesser curvature ulcer: left gastric artery.
- Vomiting of undigested food after truncal vagotomy: pylorus fails to relax; a drainage procedure is needed.
- Recurrent ulcer after highly selective vagotomy: missed criminal nerve of Grassi (exclude gastrinoma).
- Hypoglycaemia 2 hours after a sugary meal post-gastrectomy: late dumping from excess insulin.
- Exposure of D2 and pancreatic head: Kocher manoeuvre; IVC lies behind.
- Retroperitoneal gas after handlebar injury: duodenal rupture at D2–D3.
- Meckel's diverticulum: vitellointestinal duct remnant; bleeding from ectopic gastric mucosa.
Test yourself on this topic
5 of the 73 questions in our bank on this topic. Choose an answer to see why every option is right or wrong.
Which part of the stomach contains most of the G cells that secrete gastrin?
Answer: Antrum
The body and fundus contain oxyntic glands with parietal cells (HCl and intrinsic factor), chief cells (pepsinogen) and ECL cells (histamine). The antrum contains pyloric glands with G cells (gastrin) and D cells (somatostatin). Gastrin stimulates ECL cells to release histamine and parietal cells to secrete acid; it is released by peptides, vagal stimulation (via GRP) and gastric distension, and inhibited by low antral pH. Antrectomy removes the gastrin source; retained antrum after Billroth II causes high gastrin.
Gastric glands
- Body/fundus: parietal (HCl, IF), chief (pepsinogen), ECL
- Antrum: G cells (gastrin), D cells
- Gastrin → ECL histamine → acid
Remember G cells guard the gate (antrum).
Why the other options are wrong
- Fundus Parietal and chief cells.
- Body Parietal and chief cells.
- Cardia Mucous glands.
- Lesser curvature of the body only Not correct.
Which of the following nerves carry visceral pain from a chronic gastric ulcer to the spinal cord, causing dull epigastric pain?
Answer: Greater splanchnic nerves (T5–T9)
Visceral pain afferents travel back with sympathetic nerves. Those from the stomach (a foregut organ) run in the greater splanchnic nerves through the coeliac plexus to the T5–T9 segments, so the pain is felt in the epigastrium, which is supplied by the same segments. The vagus carries afferents for reflexes, fullness and nausea rather than pain. Midgut pain travels with the lesser splanchnic nerves to T10–T11 and is felt around the umbilicus.
Visceral pain pathways
- Pain fibres run with sympathetic nerves
- Foregut: greater splanchnic, T5–T9
- Felt in the epigastrium
- Vagus: nausea, fullness, not pain
Remember Pain travels with sympathetics, back to its own segments.
Exam trap The vagus does not carry visceral pain from the stomach.
Why the other options are wrong
- Vagus nerves Carries reflex and nausea afferents, not pain.
- Lesser splanchnic nerves (T10–T11) Carry midgut pain to the periumbilical area.
- Phrenic nerves Carry diaphragmatic pain to the shoulder.
- Pelvic splanchnic nerves (S2–S4) Carry pain from pelvic organs below the pelvic pain line.
An 80-year-old woman with past biliary colic has colicky pain, vomiting and distension. X-ray shows dilated small bowel, air in the biliary tree and a large opacity in the right iliac fossa. How did the stone reach the bowel?
Answer: Cholecystoduodenal fistula
In gallstone ileus, repeated inflammation makes the gallbladder adhere to the adjacent duodenum, and a large stone erodes through to form a cholecystoduodenal fistula. This is also the route by which gas enters the biliary tree (pneumobilia). The stone travels down the small bowel and impacts at the narrowest point, the terminal ileum, causing obstruction. Stones large enough to obstruct are too big to pass through the ampulla. A fistula into the colon lets the stone pass out without obstruction.
Gallstone ileus
- Gallbladder adheres to duodenum
- Stone erodes: cholecystoduodenal fistula
- Air enters bile ducts: pneumobilia
- Stone impacts at terminal ileum
Remember Air in the bile ducts shows the fistula.
Exam trap It is not a true ileus; it is mechanical obstruction.
Why the other options are wrong
- Passage through the ampulla Stones large enough to obstruct cannot pass the ampulla.
- Choledochocolic fistula Colonic fistula is less common, and the stone would bypass the small bowel.
- Perforation into peritoneum Would cause biliary peritonitis, not pneumobilia.
- Cholecystogastric fistula Uncommon; a stone here could cause gastric outlet obstruction.
A 45-year-old man with a perforated anterior duodenal ulcer has pain that began in the epigastrium but is now worst in the right iliac fossa, mimicking appendicitis. Which of the following pathways has the leaking fluid followed?
Answer: Right paracolic gutter
An anterior duodenal perforation spills into the greater sac in the right supracolic compartment. The fluid runs down the right paracolic gutter, lateral to the ascending colon, which opens freely from the hepatorenal pouch to the right iliac fossa and pelvis. This gives right iliac fossa tenderness and can mimic appendicitis (Valentino sign). The left paracolic gutter is partly closed above by the phrenicocolic ligament.
Paracolic gutters
- Anterior DU perforation: greater sac
- Fluid runs down right paracolic gutter
- RIF pain mimics appendicitis
- Left gutter: phrenicocolic ligament limits flow
Remember Upper right leaks run down to the right iliac fossa.
Exam trap Posterior gastric ulcers leak into the lesser sac; anterior duodenal ulcers leak into the greater sac.
Why the other options are wrong
- Left paracolic gutter On the left side, partly blocked by the phrenicocolic ligament.
- Lesser sac Receives posterior gastric perforations.
- Root of the mesentery Directs fluid towards the left lower quadrant.
- Retroperitoneal space Only a posterior duodenal breach leaks here.
In adhesive obstruction, X-ray shows central dilated loops crossed completely by thin, closely spaced folds. Which of the following are these folds?
Answer: Valvulae conniventes
Valvulae conniventes (plicae circulares) are permanent circular folds of mucosa and submucosa in the small intestine, most prominent in the jejunum. On X-ray, dilated small bowel shows them as thin lines crossing the whole width of the loop, giving a stacked-coin appearance, and the loops lie centrally. Colonic haustra are thicker, more widely spaced and cross only part of the width, and the colon lies peripherally.
Small vs large bowel X-ray
- Small bowel: valvulae conniventes cross fully
- Central loops, smaller diameter
- Colon: haustra cross partly
- Colon peripheral, may contain faeces
Remember Lines all the way across: small bowel.
Exam trap The terminal ileum has few folds and can look featureless.
Why the other options are wrong
- Haustra Colonic; thick and cross only part of the width.
- Taeniae coli Longitudinal muscle bands of the colon.
- Appendices epiploicae Fat tags on the colon; not seen as folds.
- Peyer patches Lymphoid tissue; not seen on plain X-ray.
Where this sits in the CPSP syllabus
- Paper 1: Abdomen, Stomach, duodenum and small intestine
- Surgery & Allied, Paper 2: Abdomen, Stomach, duodenum and small intestine
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