SU28.13 | Small Intestine and Large Intestine Anatomy — Summary & Reflection

KEY TAKEAWAYS

The intestine distal to the duodenum is two structurally distinct organs supplied along one embryological seam. The small intestine (jejunum + ileum, ~6 m) is mesentery-suspended and shows valvulae conniventes (plicae circulares) and villi; the large intestine (caecum→sigmoid + rectum, ~1.5 m) shows taenia coli, haustra and appendices epiploicae and no villi. Blood supply follows the midgut–hindgut divide: the SMA feeds the midgut (small bowel, caecum/appendix, ascending colon, proximal two-thirds of transverse colon) and the IMA feeds the hindgut (distal transverse, descending and sigmoid colon, upper rectum), linked by the marginal artery of Drummond with watershed zones at the splenic flexure (Griffiths') and rectosigmoid (Sudeck's) — the sites of ischaemic colitis. Veins drain via the portal system to the liver; lymphatics follow the arteries. Clinically, an oncological resection follows the artery and its draining nodes, an anastomosis needs good blood supply and no tension, and the wall features let you call small versus large bowel on a plain abdominal film.

REFLECT

Think back to a plain abdominal X-ray you have seen, or imagine reporting one in a patient with a distended abdomen. Could you confidently call the dilated loops small-bowel or large-bowel from the valvulae-versus-haustra and central-versus-peripheral clues — and would that change what you suspected was wrong? Now picture scrubbing for a colonic cancer operation: could you explain to the patient why the surgeon removes a whole segment of bowel with its artery and lymph nodes rather than just the lump? Reflect on how firmly holding the SMA–IMA map in your head would change the way you reason about an ischaemic colon, a bowel obstruction, and a cancer resection in the SDLs to come.