Descending colon
Colon descendens
The descending colon runs down the left flank from the splenic flexure to the left iliac fossa, where it becomes the sigmoid colon. It is secondarily retroperitoneal and part of the hindgut.
Overview
The descending colon is about 25 cm long and is narrower than the ascending colon. It lies in the left paravertebral gutter, first on the lateral border of the left kidney and then on quadratus lumborum and iliacus. It is covered by peritoneum on its front and sides; the left paracolic gutter lies lateral to it. At the pelvic brim (left iliac fossa) it becomes the sigmoid colon. By this point contents have become semi-solid faeces, so obstructing lesions here show up early as a change in bowel habit.
- Location
Left upper quadrant to left iliac fossa, along the left flank (left lumbar region).
Anatomy
- Innervation
Hindgut supply: lumbar splanchnic nerves (L1–L2) via the inferior mesenteric plexus (sympathetic) and pelvic splanchnic nerves (S2–S4), whose fibres ascend through the hypogastric plexuses (parasympathetic).
- Arterial supply
Left colic artery and the upper sigmoid arteries (IMA), via the marginal artery.
- Venous drainage
Left colic vein → inferior mesenteric vein → splenic vein (or SMV) → portal vein.
- Lymphatic drainage
Paracolic → left colic nodes → inferior mesenteric nodes.
- Relations
Posterior: left kidney (lateral border), quadratus lumborum, iliacus, transversus abdominis, and the iliohypogastric, ilioinguinal and lateral femoral cutaneous nerves. Anterior: loops of jejunum and the greater omentum.
Function
- Stores and dehydrates faeces.
- Propels faeces to the sigmoid colon and rectum by mass movements.
Clinical significance
Left-sided colon cancer
Tends to be annular and constricting (the "apple-core" lesion). Patients have a change in bowel habit, narrow stools, blood mixed with stool, and large-bowel obstruction.
Compiled from standard anatomy and physiology references — see the Digestive System sources. For education only; not medical advice.