Arterial blood supply
The arterial bed of the large intestine is formed by branches of two major abdominal aorta trunks, which supply blood to different parts of the organ.
Superior mesenteric artery (a. mesenterica superior) is responsible for the blood supply to the right half. It gives off the following successive branches:
- Ileocolic artery (a. ileocolica).
- Right colic artery (a. colica dextra).
- Middle colic artery (a. colica media).
Inferior mesenteric artery (a. mesenterica inferior) supplies the left half of the intestine and gives off the following branches:
- Left colic artery (a. colica sinistra).
- Sigmoid arteries (aa. sigmoideae). The second, third, and subsequent branches divide into ascending and descending branches. They actively anastomose both with each other and with the left colic and superior rectal arteries.
- Superior rectal artery (a. rectalis superior). This is the terminal branch of the inferior mesenteric artery, which descends toward the ampullary part of the rectum. It forms important anastomoses with the lowest sigmoid and middle rectal arteries.
Important topographical feature: only a single first-order arcade (parallel or marginal vessel) runs along the entire mesenteric border of the intestine.
Venous outflow
The venous bed of the large intestine has a two-level structure consisting of intramural (intraorgan) and extramural (extraorgan) vessels.
- Intraorgan veins form dense networks that anastomose in every layer of the intestinal wall. Converging at the mesenteric border, they form a single venous trunk running strictly parallel to the intestine.
- Extraorgan veins correspond in their course and names to the arteries. By merging, they form the superior and inferior mesenteric veins.
Special attention in topographical anatomy is deserved by the inferior mesenteric vein (v. mesenterica inferior). It passes to the left of the duodenojejunal flexure (flexura duodenojejunalis), dives under the body of the pancreas, and empties into the splenic vein. In rarer cases, it may drain directly into the portal vein.
Lymphatic system
Lymph drainage from the large intestine is a multi-step process. Lymph is collected from intraorgan networks into lymphatic vessels and passes through several barriers:
- 1st-stage nodes: located directly on the walls of the cecum, colon, and rectum, as well as along their mesenteric border.
- Subsequent-stage nodes: arranged in long chains along the branches of the superior and inferior mesenteric arteries.
- Central nodes: localized in the retroperitoneal space around the aorta and inferior vena cava (at the level of the renal vessel origins).
A massive confluence of lymphatic channels occurs anterior to the inferior vena cava. This is where lymph flows from the liver, right kidney, small and large intestine, as well as from the ovary (or testis) meet.
Innervation
Innervation of the large intestine is complex and mixed, including sympathetic, parasympathetic, and visceral sensory nerve fibers.
Sources of autonomic innervation:
- Superior mesenteric plexus (plexus mesentericus superior).
- Inferior mesenteric plexus (plexus mesentericus inferior).
- Intermesenteric plexus (plexus intermesentericus) — acts as a connecting link between the superior and inferior nodes.
- Posterior vagal trunk (truncus vagalis posterior) — provides parasympathetic fibers.
Nerve branches (rr. colici) extend from these plexuses, penetrating the thickness of the intestinal wall and forming dense intramural plexuses there.
Zones of responsibility: The cecum and the entire right half of the colon receive impulses predominantly from the superior mesenteric plexus. The left half of the colon is innervated from the inferior mesenteric plexus.
The richest receptor field throughout the entire intestine is the ileocecal region, specifically the ileocecal valve (valva ileocaecalis).
To easily remember the innervation zones, divide the large intestine in half: the right half falls under the responsibility of the "superior" mesenteric plexus, and the left half — the "inferior" one.
Class and exam questions
Which artery is the terminal branch of the inferior mesenteric artery?
Superior rectal artery (a. rectalis superior). It runs toward the ampullary part of the rectum.
Where is the venous trunk formed from intraorgan veins?
Intramural veins merge to form a main vessel that runs parallel to the intestine strictly along its mesenteric border.
Where does the inferior mesenteric vein drain?
Most commonly, it drains into the splenic vein, passing to the left of the flexura duodenojejunalis beneath the body of the pancreas. Less frequently, it empties directly into the portal vein.
What else to study on this topic
- Topography of the branches of the ileocolic and right colic arteries
- Formation of intramural autonomic plexuses from rr. colici
- Connections of the superior rectal artery with the middle rectal and sigmoid arteries
- Topography of central lymph nodes at the level of the renal vessels
- Features of the receptor apparatus of the ileocecal valve (valva ileocaecalis)
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