Anatomy chapters
Abdominal viscera
The organs of the abdomen region by region: stomach, duodenum, small and large bowel, appendix, liver, gallbladder, pancreas, spleen and kidneys, with the relations and clinical points exams use.
- The gut is divided into foregut (coeliac trunk), midgut (superior mesenteric) and hindgut (inferior mesenteric).
- The second part of the duodenum receives the bile and pancreatic ducts at the major duodenal papilla.
- Classic exam points: appendix positions and McBurney's point, Calot's triangle, jejunum vs ileum and kidney relations.
On this page
Overview
The abdomen holds most of the digestive tract and its glands, the spleen and the kidneys.
The gut is divided by its blood supply into three parts. Pain from each part is felt in a typical area: foregut in the epigastrium, midgut around the umbilicus, hindgut in the suprapubic region.
Divisions of the gut
| Part | Extends from | Artery | Pain felt in |
|---|---|---|---|
| Foregut | Lower oesophagus to the middle of the 2nd part of the duodenum; also liver, gallbladder, pancreas (upper part), spleen (artery only) | Coeliac trunk (T12) | Epigastrium |
| Midgut | Middle of 2nd part of duodenum to the junction of the right two thirds and left third of the transverse colon | Superior mesenteric (L1) | Umbilical region |
| Hindgut | Left third of transverse colon to the upper anal canal | Inferior mesenteric (L3) | Suprapubic region |
The spleen is supplied by a foregut artery (splenic, from the coeliac trunk) but develops from mesoderm, not gut endoderm.
Peritoneum
The peritoneum lines the abdominal wall (parietal) and covers organs (visceral).
- Intraperitoneal organs hang on a mesentery: stomach, first part of duodenum, jejunum, ileum, transverse and sigmoid colon, spleen, liver (mostly).
- Retroperitoneal organs lie behind it: most of the duodenum, pancreas (except the tail), ascending and descending colon, kidneys, ureters, adrenals, aorta and IVC.
The lesser sac lies behind the stomach. It opens into the greater sac through the epiploic foramen (of Winslow), whose front wall is the free edge of the lesser omentum containing the portal vein, hepatic artery and bile duct.
Squeezing the free edge of the lesser omentum (the Pringle manoeuvre) controls bleeding from the liver.
Stomach
The stomach lies in the left upper quadrant and epigastrium. Its parts are the cardia, fundus, body and pyloric part (antrum, canal and pylorus).
- Arteries: all from the coeliac trunk (left and right gastric, left and right gastro-omental, short gastric arteries).
- The stomach bed (behind it) includes the pancreas, left kidney, left adrenal, spleen and splenic artery.
A peptic ulcer on the posterior wall of the stomach can erode the splenic artery; a posterior ulcer in the duodenal cap can erode the gastroduodenal artery.
Duodenum
About 25 cm long, C-shaped around the head of the pancreas.
| Part | Level | Key feature |
|---|---|---|
| 1st (superior) | L1 | First 2.5 cm is mobile ("duodenal cap"); commonest site of duodenal ulcer |
| 2nd (descending) | L1–L3 | Bile duct and main pancreatic duct open at the major duodenal papilla |
| 3rd (horizontal) | L3 | Crossed in front by the superior mesenteric vessels |
| 4th (ascending) | L2 | Ends at the duodenojejunal flexure, held by the suspensory ligament (of Treitz) |
Jejunum and ileum
| Feature | Jejunum | Ileum |
|---|---|---|
| Position | Upper left abdomen | Lower right abdomen and pelvis |
| Wall | Thicker, wider | Thinner, narrower |
| Circular folds | Many and tall | Few or absent lower down |
| Arterial arcades | Few, with long straight vessels (vasa recta) | Many, with short vasa recta |
| Fat in mesentery | Less; "windows" seen | More; no windows |
| Lymphoid tissue | Little | Peyer's patches |
Meckel's diverticulum is a remnant of the vitelline duct on the ileum. "Rule of twos": about 2% of people, 2 feet from the ileocaecal valve, about 2 inches long; it may contain gastric tissue and bleed.
Appendix
A blind tube from the caecum, where the three taeniae coli meet.
Positions:
- Retrocaecal (behind the caecum): the commonest.
- Pelvic: the next most common.
- Others: subcaecal, preileal, postileal.
The appendicular artery (from the ileocolic artery) is an end artery, so a blocked appendix quickly becomes gangrenous.
McBurney's point lies one third of the way along a line from the anterior superior iliac spine to the umbilicus. It marks the base of the appendix.
Early appendicitis pain is felt around the umbilicus (midgut, T10). It moves to the right iliac fossa when the parietal peritoneum is irritated.
Large intestine
The colon has taeniae coli (three bands of muscle), haustra (sacculations) and appendices epiploicae (fat tags). These features distinguish it from small intestine.
The marginal artery links the superior and inferior mesenteric arteries along the colon. The splenic flexure is a watershed area at risk when blood flow is poor.
Liver
The largest gland, in the right upper quadrant under the ribs.
- Divided anatomically into right, left, caudate and quadrate lobes, and functionally into eight segments by the branches of the portal vein, hepatic artery and hepatic veins.
- The porta hepatis transmits the portal vein, hepatic artery and hepatic ducts.
- About 70–80% of its blood comes from the portal vein; the rest from the hepatic artery.
Gallbladder and bile ducts
The gallbladder lies under the liver. Its fundus touches the abdominal wall where the right linea semilunaris meets the 9th costal cartilage.
The cystic duct joins the common hepatic duct to form the bile duct. This passes behind the duodenal cap, then through the pancreatic head, to the major duodenal papilla.
Calot's (cystohepatic) triangle is bounded by the cystic duct, the common hepatic duct and the inferior surface of the liver. It contains the cystic artery.
The cystic artery is usually a branch of the right hepatic artery and lies in Calot's triangle. Surgeons identify it here during cholecystectomy.
Gallbladder pain can be referred to the right shoulder via the phrenic nerve when the diaphragm is irritated.
Pancreas
Lies across the posterior abdominal wall at about L1–L2. Parts: head (in the C of the duodenum), uncinate process, neck (in front of the portal vein), body and tail (reaching the hilum of the spleen).
Cancer of the head of the pancreas blocks the bile duct and causes painless obstructive jaundice.
Spleen
Lies in the left upper quadrant along the 9th, 10th and 11th ribs, with its long axis along the 10th rib. It is not normally felt.
It is held by the gastrosplenic and splenorenal ligaments. The splenic vessels and tail of the pancreas run in the splenorenal ligament.
Fractures of the left lower ribs can rupture the spleen. It is the abdominal organ most often injured in blunt trauma.
Kidneys
Retroperitoneal on the posterior abdominal wall, from about T12 to L3. The left kidney is higher than the right, because the liver pushes the right one down.
| Relations of the right kidney (front) | Relations of the left kidney (front) |
|---|---|
| Right adrenal, liver, 2nd part of duodenum, right colic flexure | Left adrenal, stomach, spleen, pancreas (tail), left colic flexure, jejunum |
Behind both: the diaphragm, psoas, quadratus lumborum, and the 12th rib (and 11th on the left).
At the hilum, from front to back: renal vein, renal artery, pelvis of the ureter.
Clinical relevance
Acute appendicitis
How it happens: blockage of the appendix lumen, then infection.
What you see: pain starting around the umbilicus and moving to the right iliac fossa, with tenderness at McBurney's point. A retrocaecal appendix may give back or flank pain; a pelvic one may irritate the bladder or rectum.
Splenic rupture
How it happens: blunt trauma to the left upper abdomen or lower ribs.
What you see: shock and pain, sometimes felt at the left shoulder tip (Kehr's sign).
Questions test the blood supply of each gut division, the parts and relations of the duodenum, jejunum vs ileum, Meckel's diverticulum, appendix positions and McBurney's point, Calot's triangle, the epiploic foramen, and the relations of the kidneys and spleen.
Quick revision
- Foregut: coeliac. Midgut: superior mesenteric. Hindgut: inferior mesenteric.
- Bile and pancreatic ducts open in the 2nd part of the duodenum.
- Jejunum: long vasa recta, few arcades. Ileum: short vasa recta, many arcades, Peyer's patches.
- Appendix: commonest position retrocaecal; McBurney's point one third from ASIS to umbilicus.
- Calot's triangle: cystic duct, common hepatic duct, liver; contains the cystic artery.
- Spleen along ribs 9–11. Left kidney higher than right.
Written by The House Job from standard anatomy references (Snell's Clinical Anatomy by Regions is the book named in the UHS PGET syllabus).
FAQ
Where does the common bile duct open?
Into the second part of the duodenum, at the major duodenal papilla, usually together with the main pancreatic duct.
What is the commonest position of the appendix?
Retrocaecal.
What is in Calot's triangle?
The cystic artery, and usually the cystic lymph node (of Lund).
Why is early appendicitis pain felt around the umbilicus?
The appendix is a midgut organ, and visceral pain from the midgut is referred to the T10 dermatome around the umbilicus.