anus

Eva Rudolf-Müller is a freelance writer in the medical team. She studied human medicine and newspaper sciences and has repeatedly worked in both areas - as a doctor in the clinic, as a reviewer, and as a medical journalist for various specialist journals. She is currently working in online journalism, where a wide range of medicine is offered to everyone.

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The anus (anus, anal canal) forms the end of the rectum. Stool evacuation (defecation) takes place through it. Disturbances in the area of ​​the anal canal lead to severe impairments for those affected. Read everything you need to know about the anus!

What is the anus?

The anus, also called the anal canal, is the lowest end of the rectum. It is divided into three areas from top to bottom:

Zona columnaris: The mucous membrane here has six to eight longitudinal dorsal columns with indentations in between. Under the mucous membrane lies a vascular cushion (corpus cavernosum recti), which causes the anus columns to attach to one another through the filling of blood. This closes the anal canal, so it contributes to continence. In the case of a pathological, nodular expansion of the vascular cushion, one speaks of "internal hemorrhoids".

Zona intermedia: It is also called the zona alba because of the light-colored mucous membrane. The venous plexus located here forms the so-called "external hemorrhoids" when the disease is widened.

Zona cutanea: It borders on the external sphincter muscle and resembles the skin with stronger pigmentation and sebum and sweat glands.

The sphincters on the anus

The circular muscle layer of the large intestine wall is reinforced in the anus to form a strong internal sphincter, which works involuntarily - so it cannot be deliberately influenced. The external sphincter lies above this and can be influenced at will.

The two sphincters together have a strong tone that can be felt when trying to insert a suppository or when the doctor wants to do a rectal exam. In addition to the muscular closure, there is the venous plexus of the zona haemorrhoidalis, the filling of which guarantees a tight closure.

What is the function of the anus?

The anal canal is used for bowel evacuation (defecation), which is a complex process. The peristalsis of the muscular wall of the colon (the upstream section of the large intestine) transports the feces into the rectum. Its filling leads to a relaxation of the internal sphincter muscle and an increased contraction of the external sphincter muscle. The urge to defecate becomes noticeable, but this can be suppressed by consciously keeping the external sphincter muscle in contraction.

If, on the other hand, you relax it consciously, defecation occurs, driven by peristaltic contractions of the colon and rectum. Tensing the abdominal muscles can encourage defecation.

What problems can the anus cause?

A perianal thrombosis is a venous thrombosis on the outer edge of the anus. The veins of the closing apparatus are affected, which form a reddened lump at the edge of the anus due to the thrombus.

Hemorrhoids (more precisely: a hemorrhoidal disease) can be noticeable, for example, as bright red blood stains on the faeces or toilet paper.

An anal abscess is an acute, enclosed, purulent inflammation around the anus caused by bacterial infection of the anal glands. In the case of an anal fistula, the inflammation has opened a tubular duct from the anal canal through the body, through which secretion and pus drain away.

With an anal fissure, the skin in the anal canal is torn, for example from hard stools or frequent diarrhea.

In the case of anal prolapse, the anal canal bulges outward when the patient is pressed hard while the toilet is defecated.

Malignant tumors (carcinomas) rarely occur in the anus area.

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