Hemorrhoid tissues are “cushions” of blood vessels that swell slightly during bowel movements. Too much pressure on the anal canal can make these tissues remain enlarged, become inflamed, and cause symptoms. This can happen both inside and outside the anal canal.
Parts of the anal canal
The parts of the anal canal are:
Internal hemorrhoid tissue is in the upper area of the anal canal.
The rectum is the last several inches of the colon. This is where stool is stored prior to bowel movements.
Anal sphincters are ring-shaped muscles that expand and contract to control the anal opening.
External hemorrhoid tissue lies under the anal skin.
The anus is the passage between the rectum and the outside of the body.
Normal hemorrhoid tissue
Hemorrhoid tissues play an important role in helping your body eliminate waste. Food passes from the stomach through the intestines. The waste (stool) then travels through the colon to the rectum. It is stored in the rectum until it’s ready to be passed from the anus. During bowel movements, hemorrhoids swell with blood and become slightly larger. This swelling helps protect and cushion the anal canal as stool passes from the body. Once the stool has passed, the tissues stop swelling and return to normal.
Pressure due to straining or other factors can cause hemorrhoid tissues to remain swollen. When this happens to the hemorrhoid tissues in the anal canal they’re called internal hemorrhoids. Swollen tissues around the anal opening are called external hemorrhoids. Depending on the location, your symptoms can differ.
Internal hemorrhoids often happen in clusters around the wall of the anal canal. They are usually painless. But they may prolapse (protrude out of the anus) due to straining or pressure from hard stool. After the bowel movement is over, they may then reduce (return inside the body). Internal hemorrhoids often bleed. They can also discharge mucus.
External hemorrhoids are located at the anal opening, just beneath the skin. These tissues rarely cause problems unless they thrombose (form a blood clot). When this happens, a hard, bluish lump may appear. A thrombosed hemorrhoid also causes sudden, severe pain. In time, the clot may go away on its own. This sometimes leaves a “skin tag” of tissue stretched by the clot.
Hemorrhoid symptoms may include:
Pain or a burning sensation
Bleeding during bowel movements
Protrusion of tissue from the anus
Itching around the anus
Causes of hemorrhoids
There’s no single cause of hemorrhoids. Most often, though, they are caused by too much pressure on the anal canal. This can be due to:
Chronic (ongoing) constipation
Straining during bowel movements
Sitting too long on the toilet
Strenuous exercise or heavy lifting
Pregnancy and childbirth
March 21, 2017
Patient Information: Hemorrhoids (Beyond the Basics). UpToDate
Adler, Liora C., MD,Image reviewed by StayWell medical illustration team.,Sather, Rita, RN