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The mesenteric vessels in a mobile segment of bowel such as small bowel, transverse or sigmoid colon can be visualized by transillumination and more safely secured than by blind mass clamping of mesentery.
The rectal blood supply comes from three sources: from the terminal branch of the IMA, the superior rectal, running in the mesorectum; from the middle rectals off the internal iliacs above the pelvic diaphragm; and from the inferior rectals off the pudendals running beneath the pelvic diaphragm.
The venous drainage of abdominal viscera converges in the portal vein which passes the blood through the liver sinusoids before emptying into the systemic circulation of the inferior vena cava (IVC). Disruption of the hepatic architecture by disease (hepatitis, parasites) or alcohol toxicity leads to cirrhosis and resistance to portal flow. The resulting increased portal pressure manifests in hypertrophied porta-systemic communications (esophageal varices, hemorrhoids and umbilical vein recanalization).