of superior rectal veinor superior hemorrhoidal veinconnects the veins around the rectum to the inferior mesenteric vein.
The inferior mesenteric vein carries blood from the large intestine to the splenic vein. Blood in the spleen is sent to the liver. Blood is filtered from the liver and ultimately sent to the heart, where it is further oxygenated before being circulated throughout the body. The rectal vein is the main connection between blood from all the veins around the rectum.
When the tributaries of the veins swell, they are pushed into the rectum, internal hemorrhoids. Internal hemorrhoids may cause blood to appear on the surface of the stool. Internal hemorrhoids may indicate a serious medical problem and should be seen by a doctor.
Hemorrhoids occur when the rectal veins become compressed and block blood flow. During pregnancy, the weight of the fetus affects blood flow in the veins. Cancerous growths within the rectum can block the veins. Rectal contractions also affect blood flow in the superior rectal veins.