Answer to Look Before You Flush

Question: Dilated veins in the indicated region drain to which of the vessels in the list?

Correct answer is C, the middle rectal veins. The indicated area is the rectum, approximately at the pectinate line. This area is at the interphase where the endoderm and ectoderm met during development. Hence, it is supplied by somatic nerves and arteries from the internal iliac, but below the mucosa will be the internal rectal plexus that will drain to the portal system of veins.   Hemorrhoids below the pectinate line are close to the anal canal and will be painful and itchy. Above the pectinate line the hemorrhoids are painless. Both types of hemorrhoids are the result of a persistent increase in venous pressure. The internal hemorrhoids may be due to portal hypertension.

Answer to this question is based on material presented in lectures 3 of the Pelvis Lecture Series.