29 Pelvic Blood Supply

Blood supply and innervation of the male and female pelvic organs:

Blood supply:

The blood supply of the internal urogenital organs of the male and female pelvis is different from the GI tract. The pelvic portion of the GI tract (part of the sigmoid colon and the rectum) receives blood from branches of the inferior mesenteric artery. At the end of the rectum is the anus which is supplied from the terminal branches of the internal iliac artery. In contrast, the urogenital organs of the pelvis are entirely supplied by branches of internal iliac artery.

The venous drainage of the pelvis is via the iliac vein except for the GI system. The GI organs of the pelvis drain into the portal system (i.e., they go to the hepatic portal vein) except for the anus which has some drainage to the caval system (i.e., they drain directly to the vena cava) like the rest of the pelvic organs.

Innervation:

Innervation of the pelvic organs occurs via both the parasympathetic and sympathetic nervous system.  Parasympathetic nerves stimulate smooth muscle contractions in the GI tract and bladder to cause defecation and urination respectively. To allow feces and urine to be expelled, there are internal, smooth muscle sphincters which relax as part of the urination and defecation reflexes. In contrast to the internal sphincters, the external sphincters are striated muscle and under somatic nerve control which is voluntary.

Sexual response is complex in male and females. The parasympathetic nerves are necessary for arousal which leads to increased blood flow for engorgement of the external genitalia but it is the sympathetic nervous system which is necessary for orgasm.