Descending colon !
The descending colon is the part of the large intestine that runs down the left side of the belly, carrying formed stool toward the sigmoid colon.
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What it is
The part of the colon running down the left side.
What it does
Stores and moves stool down toward the sigmoid.
Key facts
- Where
- Left flank, from splenic flexure to pelvic brim; secondarily retroperitoneal
- Blood supply
- Left colic artery (IMA); marginal artery
- Nerve
- Inferior mesenteric plexus (sympathetic, lumbar splanchnic L1–L2); pelvic splanchnic nerves (S2–S4)
- Function
- Stores and propels stool toward sigmoid; absorbs water
Relations
- Behind
- Lateral border of the left kidney, quadratus lumborum, iliacus and psoas, with the iliohypogastric, ilioinguinal and lateral femoral cutaneous nerves
- Lateral
- Left paracolic gutter, closed above by the phrenicocolic ligament
- Medial
- Loops of jejunum; deeper, the inferior mesenteric vein, the left ureter and the gonadal vessels
- In front
- Loops of small intestine and the greater omentum; in thin people, the anterior abdominal wall
- Above
- Splenic flexure, below the spleen and the tail of the pancreas
How to find it
It projects onto the left flank. Hard stool can sometimes be felt in it as a mass that can be indented, unlike a tumor. At colonoscopy it is a fairly straight segment between the splenic flexure and the sigmoid.
On imaging
In ischemic colitis near the splenic flexure, X-ray or CT shows wall thickening and «thumbprinting» from submucosal edema. In long-standing ulcerative colitis, barium enema shows a featureless lead-pipe colon without haustra.
Common problems
- Colon polyps and colorectal cancer: screening finds them early.
- Diverticular disease and diverticulitis (usually sigmoid).
- Ulcerative colitis and Crohn disease.
How it is diagnosed
Colonoscopy; CT; stool tests for screening.
Treatment
- Polyps removed during colonoscopy; surgery (colectomy) for cancer or complicated disease.
Clinical notes
- Ischemic colitis favors the watershed near the splenic flexure (Griffiths point), for example after low blood flow or aortic surgery that sacrifices the inferior mesenteric artery
- The phrenicocolic ligament stops fluid in the left paracolic gutter from reaching the area around the spleen, so it drains toward the pelvis
- Pain from the descending colon (hindgut) is felt in the suprapubic region
Development
A hindgut derivative supplied by the inferior mesenteric artery. Its mesentery fuses with the back wall in most people, leaving the bloodless plane opened in a left colectomy; in a minority part of a descending mesocolon remains and the segment is more mobile.
Related conditions
- Diverticular disease and diverticulitis
- Large bowel obstruction
- Ulcerative colitis
- Irritable bowel syndrome
- Lower gastrointestinal bleeding
- Clostridioides difficile infection
- Ischaemic colitis
- Hemolytic uremic syndrome (HUS)
Test yourself
Think of the answer, then tap the question to see it.
Why do cancers of the descending colon tend to obstruct while right-sided ones bleed silently?
The left colon is narrower and carries formed stool, so tumors obstruct and change bowel habit.
Which structures lie behind the fusion plane of the descending colon in a left colectomy?
The left ureter and the gonadal vessels, which must be identified.
Which artery supplies the descending colon?
The left colic artery from the inferior mesenteric artery, plus the marginal artery.
Educational information, not medical advice. For any symptom, see a health professional.
Its names
- Official Latin (TA2)
- colon descendens TA2 2986
- Official Spanish (DeCS)
- Colon descendente DeCS D044683
- English (TA2)
- Descending colon
- Also called
- left colon
Related
Sources: Terminologia Anatomica (TA2); DeCS; Anatomy, Abdomen and Pelvis: Large Intestine; 23.5 The Small and Large Intestines (OpenStax (Rice University), 2022) · adapted, CC BY 4.0; Anatomy of the Human Body (20th ed.): The Digestive Apparatus (Lea & Febiger (Gray's Anatomy, 1918), 1918) · adapted, Public domain.
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Representative model, for educational purposes only.
