Arterial bed of the ascending and transverse parts
The ascending colon receives arterial blood from two main sources: branches of the right colic artery (a. colica dextra) and the middle colic artery (a. colica media).
The topography of a. colica dextra has important features. The vessel runs retroperitoneally, lying behind the parietal peritoneum, and courses strictly toward the middle of the ascending colon. At a distance of about 4–6 centimeters from the intestinal wall, the artery bifurcates into two branches, each of which participates in the formation of anastomoses:
- Ascending branch: runs upward and anastomoses with the right (descending) branch of a. colica media.
- Descending branch: runs downward, where it forms a junction with the ascending branch of the ileocolic artery (a. ileocolica).
The transverse colon is vascularized by a. colica media and the left colic artery (a. colica sinistra). The middle colic artery courses toward the right third of the transverse colon. Here, it also divides into two trunks:
- Right (descending) branch: connects with a. colica dextra.
- Left (ascending) branch: courses to the left and anastomoses with the ascending branch of a. colica sinistra.
Blood supply to the left half of the colon
The descending colon is supplied predominantly from the basin of the inferior mesenteric artery (a. mesenterica inferior), from which the left colic artery (a. colica sinistra) branches off.
The course of this vessel has clear topographical and anatomical landmarks. The artery runs retroperitoneally in the left mesenteric sinus (sinus mesentericus sinister). An important surgical fact: along its path, it passes anterior to the left ureter. Upon reaching the region of the left colic flexure, a. colica sinistra divides into two branches:
- Ascending branch: ascends upward and takes part in the formation of Riolan's arch.
- Descending branch: descends downward, where it reliably anastomoses with the first sigmoid artery.
The sigmoid colon receives its blood supply from the sigmoid arteries (aa. sigmoideae), which are also branches of a. mesenterica inferior. Anatomically, there are 2 to 4 such branches. Their course varies: the initial segment lies retroperitoneally, after which the vessels penetrate between the leaves of the sigmoid mesocolon. A distinctive feature of this group of vessels is that the first sigmoid artery is always the most robust and largest.
Riolan's arch and intersigmoid recess
A special place in the topographical anatomy of the large intestine is occupied by Riolan's arch. This is a robust arterial anastomosis located directly within the transverse mesocolon. Its uniqueness lies in the fact that it connects the two main vascular basins of the abdominal cavity:
- The superior mesenteric artery system (represented by the left branch of a. colica media).
- The inferior mesenteric artery system (represented by the ascending branch of a. colica sinistra).
When studying the region of the sigmoid colon, attention must be paid to the intersigmoid recess (recessus intersigmoideus). This anatomical structure is quite common.
- Shape of the cavity: can be funnel-shaped or cylindrical.
- Entrance opening: usually has a round or oval shape and opens into the left paracolic gutter.
- Boundaries of the recess: anteriorly it is bounded by the sigmoid mesocolon, and posteriorly it lies adjacent to the parietal peritoneum.
Briefly: answers to topical questions
Which vessels do the sigmoid arteries anastomose with?
The sigmoid arteries anastomose with each other and also with branches of the left colic and superior rectal arteries.
- Left colic artery (a. colica sinistra) — its descending branch anastomoses with the first sigmoid artery.
- Superior rectal artery (a. rectalis superior) — forms anastomoses with the lowest sigmoid artery.
- Sigmoid arteries (aa. sigmoideae) — give off ascending and descending branches that form anastomoses with each other.
Which arteries form Drummond's marginal artery?
Drummond's marginal artery (marginal vessel) is formed by anastomoses between branches of the superior and inferior mesenteric arteries along the border of the bowel. The key segment of this arch is formed by:
- Middle colic artery (a. colica media) — its left branch.
- Left colic artery (a. colica sinistra) — anastomoses with the left branch of the middle colic artery.
The ascending branch of the ileocolic artery (a. ileocolica) also takes part in the formation of the marginal artery.
Which veins form the venous drainage from the right half of the colon?
Venous drainage from the right half of the large intestine is carried out into the superior mesenteric vein basin (v. mesenterica superior). It is formed by the following vessels:
- Ileocolic vein (v. ileocolica) — collects blood from the ileocecal angle.
- Right colic vein (v. colica dextra) — drains blood from the ascending colon.
- Middle colic vein (v. colica media) — collects blood from the transverse colon.
What is the innervation of the transverse colon?
The innervation of the transverse colon depends on the segment.
- Up to the level of the left colic flexure, parasympathetic innervation is provided by the vagus nerve (n. vagus).
- Distal to the left colic flexure, parasympathetic innervation is provided by the sacral spinal cord segments (S2–S4) via the pelvic splanchnic nerves (nn. splanchnici pelvini).
- The cecum and the right half of the colon are innervated predominantly from the superior mesenteric plexus.
To remember the formation of Riolan's arch, use the rule "Middle to the left, Left upward": the left branch of the middle colic artery (a. colica media) meets the ascending branch of the left colic artery (a. colica sinistra).
Class and exam questions
Where exactly does the left colic artery run in relation to the ureter?
The left colic artery (a. colica sinistra) runs retroperitoneally in the left mesenteric sinus strictly anterior to the left ureter.
Which vessels form Riolan's arch?
Riolan's arch is formed by the left branch of the middle colic artery (a. colica media) and the ascending branch of the left colic artery (a. colica sinistra). This anastomosis is located in the transverse mesocolon.
Which of the sigmoid arteries is the largest?
Out of 2–4 sigmoid arteries (aa. sigmoideae) supplying this segment, the first sigmoid artery is always the most robust.
What are the boundaries of the intersigmoid recess?
Anteriorly, the intersigmoid recess (recessus intersigmoideus) is bounded by the sigmoid mesocolon, and posteriorly by the parietal peritoneum. It opens into the left paracolic gutter.
What else to study on this topic
- Topography and branching variants of a. colica dextra
- Anastomoses between a. colica media and a. colica dextra
- Structure and boundaries of the left mesenteric sinus (sinus mesentericus sinister)
- Topography of the intersigmoid recess (recessus intersigmoideus)
- Relationship of a. colica sinistra with the left ureter
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