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Anus

from Latin: anus - ring
Synonym: opening of the digestive tract
German: Anus

1 Definition

The anus is the orifice or excretion opening of the intestines. Its purpose is to control defecation.

2 Anatomy

2.1 Continence organ

The anus has 2 important sphincters:

These two muscles control defecation together with the levator ani muscle and thereby form the closing apparatus of the rectum. The functional unit from these muscles and the venous plexus of the anus (corpus cavernosum recti) is also called the continence organ.

2.2 Anal canal

The terminal section of the intestines modeled by the sphincter muscles is called anal canal. It is around 2-4 cm long, is framed by the pelvic floor and therefore has no peritoneal cover. In closed state, it presents as longitudinal slit running in anterio-posterior direction.

The transition to the rectum is marked by the curled anorectal junction or dentate line to the side of the lumen. Here, the highly prismatic columnar epithelium of the rectal mucosa transitions into the uncornified squamous epithelium of the anal mucosa. Caudal to this line, you can see around 8-10 mucosal folds raised by the muscle strains of the internal anal sphincter, the anal columns (Morgagniís columns). In this region, the corpus cavernosum recti, a spongy body supplied by the superior rectal artery can also be found.

On the base of the anal columns, sail-like valves are callling attention, the anal valves. They mark the entrance to the anal crypts. In the depth, the anal or proctodeal glands can be found. Below the anal valves, the zone where the anal mucosa transitions into the external skin begins. It is called anal pecten, or also - due to its light color - zona alba. It ends at the anocutaneous linem which also represents the caudal delimitation of the anal canal.

2.3 Topography

On its dorsal side, the anus is connected to the coccyx via the anococcygeal ligament. On the ventral side, separated by connective and muscular tissue, you can find the urethra in men, and the vagina in women in close proximity.

3 Clinical presentation

The most important diseases of the anus include:

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