Anal conditions: Clinical

The anus is the final 3 to 4 centimeters of the gastrointestinal tract, and it extends from the rectum to the anal margin.

The top and bottom of the anal canal are surrounded by the internal and the external anal sphincters, which are two muscular rings that control defecation.

The internal sphincter is under involuntary control, while the external sphincter is under voluntary control.

Within the anal canal, there are mucosal membrane infoldings that form the anal columns.

And at the base of these columns, there is the dentate or pectinate line, which divides the upper two thirds and lower third of the anal canal.

Above the dentate line, there’s the mucosa is lined by simple columnar epithelium, and below the dentate line, there’s the anoderm, which has no hair and sebaceous and sweat glands, and is lined by squamous epithelium.

Now, hemorrhoids are normal vascular structures in the anal canal that act as cushions for the stool as it passes through.

Hemorrhoidal disease is when hemorrhoids get swollen or inflamed; but the term "hemorrhoid" is often used to refer to the disease.

Hemorrhoids are often caused by chronically or recurrently increased abdominal pressure, from a variety of causes.

For example, straining during bowel movements, chronic diarrhea or constipation, obesity, pregnancy, and old age.

Complications of hemorrhoids can include anemia due to chronic blood loss; strangulation if the blood supply to an internal hemorrhoid is cut off, leading to ischemia; and thrombosed hemorrhoids, which is when blood pools inside a hemorrhoid and forms clots.