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Overview of the Anus and Rectum

By

Parswa Ansari

, MD, Hofstra Northwell-Lenox Hill Hospital, New York

Last full review/revision Feb 2021| Content last modified Feb 2021
CLICK HERE FOR THE PROFESSONAL VERSION
Topic Resources

The Digestive System

The Digestive System

The anus is formed partly from the surface layers of the body, including the skin, and partly from the intestine. The rectal lining consists of glistening red tissue containing mucus glands—much like the rest of the intestinal lining. The lining of the rectum is relatively insensitive to pain, but the nerves from the anus and nearby external skin are very sensitive to pain.

The veins from the rectum and anus drain mostly into the portal vein, which leads to the liver, and then into the general circulation. Some of these veins drain directly into the pelvic veins and then into the general circulation. The lymph vessels of the rectum drain into lymph nodes in the lower abdomen. The lymph vessels of the anus drain into the lymph nodes in the groin.

A muscular ring (anal sphincter) keeps the anus closed. This sphincter is controlled subconsciously by the autonomic nervous system Autonomic nervous system The peripheral nervous system consists of more than 100 billion nerve cells (neurons) that run throughout the body like strings, making connections with the brain, other parts of the body, and... read more . However, part of the sphincter can be relaxed or tightened at will.

Disorders of the anus and rectum include

Diagnosis of Anal and Rectal Disorders

  • A doctor's evaluation

  • Anoscopy or sigmoidoscopy

  • Possibly computed tomography (CT) scan or magnetic resonance imaging (MRI)

To diagnose disorders of the anus and rectum, a doctor inspects the skin around the anus for any abnormality. With a gloved finger, the doctor probes the rectum. For women, this is often done along with a manual examination of the vagina (see Gynecologic Examination Gynecologic Examination For gynecologic care, a woman should choose a health care practitioner with whom she can comfortably discuss sensitive topics, such as sex, birth control, pregnancy, and problems related to... read more ). Doctors often also examine the abdomen.

Next, a doctor looks into the anus and rectum with a 3- to 10-inch (about 7- to 25-centimeter) rigid viewing tube (anoscope or proctoscope). A longer, flexible tube (sigmoidoscope) may then be inserted so that the doctor can observe as much as 2 or more feet of the large intestine.

An anoscopy or sigmoidoscopy (see Endoscopy Endoscopy Endoscopy is an examination of internal structures using a flexible viewing tube (endoscope). Endoscopy can also be used to treat many disorders because doctors are able to pass instruments... read more ) is generally uncomfortable but not painful. However, if the area in or around the anus is painful because of an abnormal condition, the doctor may apply a numbing ointment (such as lidocaine) or give a local, regional, or even general anesthetic Anesthesia Surgery is the term traditionally used to describe procedures (called surgical procedures) that involve manually cutting or stitching tissue to treat diseases, injuries, or deformities. However... read more before proceeding with the examination. Sometimes a cleansing enema to rid the lower part of the large intestine of stool is given before sigmoidoscopy.

NOTE: This is the Consumer Version. DOCTORS: CLICK HERE FOR THE PROFESSONAL VERSION
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Eosinophilic Esophagitis
Eosinophilic esophagitis is an inflammatory disorder in which the wall of the esophagus, the tube leading from the throat to the stomach, becomes filled with a type of white blood cells called eosinophils. Which of the following is believed to be the cause of this disorder?
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