Hemorrhoids are swollen clumps of vessels, smooth muscle and connective tissue in the anus and lower rectum. They are similar to varicose veins, but they are not considered the same. Hemorrhoids are quite common; about 75% of adults will have hemorrhoids in their life. Sometimes they are very benign; other times they may cause significant symptoms, such as itching, pain, prolapse and rectal bleeding.
Hemorrhoid cushions are a normal part of the body and only pose an issue when become engorged, prolapsed and inflamed. In their normal state, they have an important role in continence, and make up 15-20% of anal pressure at rest. When bearing down, the cushions expand to maintain anal closure as intra-abdominal pressure grows. Increased sphincter pressure may result due to hemorrhoid inflammation because of this effect.
Hemorrhoids are classified into internal and external hemorrhoids. Internal hemorrhoids develop deeper in the rectum, above the dentate line, from the embryonic endoderm and are covered by columnar epithelium. There are few somatic sensory nerves in this area, and as a result are not painful. Patients often only notice the blood after a bowel movement as a result of internal bleeding. External hemorrhoids are located around the anus, below the dentate line, derived from the ectoderm and covered in squamous epithelium. There are many sensory nerves here, so external hemorrhoids can be quite painful when the complication of thrombosis happens.
Hemorrhoid inflammation is often caused by excess pressure in the region. This can be exacerbated by straining when defecating, constipation/diarrhea, low-fiber content in diet, lack of fluid, sitting too long, weight, and lack of exercise. Proper rectal function and physical fitness are essential in preventing hemorrhoid formation.