IN THIS ARTICLE
What is the difference between an internal, external, or thrombosed hemorrhoid?
What causes hemorrhoids?
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Hemorrhoids are not arteries or veins, but instead are normal blood vessels called sinusoids that are located in the walls that surround the rectum and anus. When the venous pressure within these blood vessels increases, the hemorrhoids swell and dilate, because it is more difficult for blood to empty from them. This leads to the most common symptoms of bleeding and swelling.
Common situations that increase pressure within the hemorrhoidal blood vessels and lead to abnormalities include the following.
Medically Reviewed by a Doctor on 6/6/2016
Bhupinder Anand, MD
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