Upper Limb  
  Lower Limb  
rectum - close-up
Hemorrhoids occur when normal venous dilitations in the submucosa ‘loosen’ and bulge out. Internal hemorrhoids are insensitive to somatic pain and are located superior to the dentate line, whereas external hemorrhoids are sensitive to somatic pain and lie below the dentate line. This is why internal hemorrhoids may be treated by rubberband ligation.
Anorectal varices may be distinguished from hemorrhoids because varices will disappear when pressure is applied to them and reappear rapidly when pressure is released.

The pelvic plexus surrounds the rectum. In males, postganglionic parasympathetic fibers (after pelvic splanchnic nerves have synapsed in the pelvic plexus) descend inferiorly on the posteriolateral surface of the prostate are called cavernous nerves. These nerves send innervation to the corpora cavernosa and thus damage to these nerves (at high risk during prostate surgery) can lead to impotence.
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