MRCS Part B Revision · Anatomy
Small Intestine — MRCS Part B Anatomy
By Dr Richard Miller, MBChB FRCS · Reviewed
Small Intestine is a surgical anatomy station. Three of the seventeen examined stations in the MRCS Part B OSCE are surgical anatomy. The anatomy stations put a prosected specimen, a model or an image in front of you and ask you to identify structures and say what they do, what they relate to and what happens when they are injured.
What you need to know for the Small Intestine station
The duodenum, jejunum and ileum, then the aorta and the three gut arteries, which is where most of the questions sit.
The duodenum
About 25 cm, C-shaped around the head of the pancreas, retroperitoneal apart from its first 2–3 cm. The first part runs back from the pylorus at L1, above the head of the pancreas, with the gastroduodenal artery behind it. The second part descends from L1 to L3 in front of the right kidney and receives the bile and pancreatic ducts at the major papilla, about halfway down, on its posteromedial wall. The third part crosses L3 from right to left, behind the superior mesenteric vessels and in front of the aorta and inferior vena cava. The fourth part rises to the duodenojejunal flexure at L2, held by the suspensory ligament of Treitz. Its wall has Brunner's glands in the submucosa, secreting alkaline mucus.
Blood supply is from both the coeliac trunk (superior pancreaticoduodenal artery, a branch of the gastroduodenal) and the superior mesenteric artery (inferior pancreaticoduodenal), meeting on the pancreatic head. A posterior duodenal ulcer or tumour matters because the gastroduodenal artery lies directly behind the first part: erosion into it causes a major haematemesis, and a posterior perforation is retroperitoneal, with less peritonitis and a later presentation.
Transpyloric plane
A horizontal plane at L1, halfway between the suprasternal notch and the pubic symphysis. It passes through the pylorus, the duodenojejunal flexure, the neck of the pancreas, the hila of the kidneys (the left slightly above, the right below), the fundus of the gallbladder, the origin of the superior mesenteric artery, the formation of the portal vein, the ninth costal cartilages and the end of the spinal cord.
Jejunum and ileum
The jejunum is the proximal two-fifths, in the upper left abdomen, wider and thicker-walled with tall circular folds felt through the wall, a redder colour, long straight vasa recta and few arcades, with little fat in the mesentery. The ileum is narrower, thinner and paler, with short vasa recta, many arcades, fat reaching the bowel wall, and Peyer's patches in its lower part. The jejunum absorbs most nutrients; the ileum absorbs vitamin B12 with intrinsic factor and reclaims bile salts in its terminal part, which is why terminal ileal disease or resection causes B12 deficiency and bile-salt diarrhoea.
The abdominal aorta
Enters at T12 through the aortic hiatus, runs down on the vertebral bodies to the left of the midline with the inferior vena cava on its right, and divides at L4 (the level of the iliac crests). Branches: three unpaired anterior (coeliac T12, superior mesenteric L1, inferior mesenteric L3), paired lateral (inferior phrenic, suprarenal, renal, gonadal) and posterior (lumbar and median sacral).
The three gut arteries
- Coeliac trunk — left gastric, splenic and common hepatic arteries. It supplies the foregut: lower oesophagus, stomach, first half of the duodenum, liver, gallbladder, pancreas and spleen.
- Superior mesenteric artery — inferior pancreaticoduodenal, jejunal and ileal branches, ileocolic, right colic and middle colic. It supplies the midgut, from the second half of the duodenum to two-thirds along the transverse colon.
- Inferior mesenteric artery — left colic, sigmoid branches and the superior rectal artery. It supplies the hindgut to the upper anal canal.
Images from this station
What are you asked at the Small Intestine station?
The station runs to 18 questions over nine minutes. A prompt the station repeats — against each marker on a specimen, for instance — is listed once here; the model answers are in the question bank.
- Describe the course of the duodenum
- What is the blood supply of the duodenum?
- What is the significance of a posterior duodenal ulcer or tumour?
- What is the transplyloric plane and at what vertebral level is it located?
- What structures are found at the level of the transplyoric plane?
- Describe the differences between the jejunum and ileum
- Describe the structure of the duodenum
- Describe the structure of the jejunum
- What is the function of the ileum?
- What are the branches of the abdominal aorta?
- Describe the path and relations of the aorta in the abdomen
- What are the branches of the coeliac artery?
And 5 more at this station.
How is the anatomy station marked in MRCS Part B?
An anatomy station is marked out of 20, and all 20 marks go to clinical knowledge and its application. No communication, technical-skill or professionalism marks are available in an anatomy bay, which is unusual: in most other stations more than half the marks sit outside your factual knowledge.
FAQ
What does the Small Intestine station ask?
It opens with "Describe the course of the duodenum" and runs to 18 questions over nine minutes. An anatomy station is marked out of 20, and all 20 marks go to clinical knowledge and its application. No communication, technical-skill or professionalism marks are available in an anatomy bay, which is unusual: in most other stations more than half the marks sit outside your factual knowledge.
How many anatomy stations are there in MRCS Part B?
Three of the seventeen examined stations are surgical anatomy, and two more are surgical pathology. Together they make up the five Anatomy and surgical pathology stations of the Applied Knowledge component.
How are the anatomy stations marked?
Each station is marked out of 20 and all 20 marks are awarded for clinical knowledge and its application. You also receive a separate global rating of pass, borderline or fail for the station.
Are the specimens real?
Yes. Anatomy bays use prosected cadaveric specimens, models and images. Candidates report being shown photographs of specimens as well as the specimens themselves, so practise on real dissection photography rather than diagrams alone.
What happens if I get an early question wrong?
The intercollegiate guidance says that if a wrong answer would affect your performance on later questions at the same station, the examiner gives you the correct answer before moving on. One mistake does not have to cost you the whole bay.
How many stations are in the MRCS Part B OSCE?
Seventeen examined stations of nine minutes each, with a minute to read the task before each one. Two preparation stations and at least one rest station bring the circuit to about twenty, and the exam takes about three and a half hours.
What is the pass mark for MRCS Part B?
There is no published pass mark. The cut score is set separately for Applied Knowledge and Applied Skills, for each circuit, by borderline regression. Published pass rates across the 2024/25 diets ranged from 51% to 66%.
Can I fail a station and still pass?
Yes. There is no rule about how many stations you may fail: the cut score applies to your total mark in each component, so a weak station costs the marks you lost on it and strong stations elsewhere can make them back. Applied Knowledge and Applied Skills are passed separately and must both be passed at the same sitting, so a strong anatomy performance cannot rescue a weak communication one.
Dr Richard Miller, MBChB FRCS
Station summaries are reviewed against the current intercollegiate MRCS syllabus and the published marking blueprint. Guidance changes between diets: check the royal colleges' own pages before relying on a date, a fee or a threshold.
Practise this station
The question bank carries the model answer to every question above, with the rest of the anatomy stations.
More anatomy stations