"Anus" - what is it, definition of the term
The terminal opening of the gastrointestinal tract, located at the posterior extremity of the body, serves as the exit point for fecal matter and is encircled by a circular and longitudinal sphincter muscle complex that controls the release of contents and preserves continence.
Detailed information
The anal opening marks the termination of the gastrointestinal tract. It is surrounded by the internal and external sphincters, smooth and skeletal muscle layers that maintain continence and permit controlled evacuation. Innervation derives from the pudendal nerve and autonomic fibers, providing sensory feedback and reflex coordination.
Continence results from tonic contraction of the internal sphincter and voluntary control of the external sphincter. Defecation initiates when rectal pressure exceeds sphincter tone, triggering relaxation and coordinated muscle activity that expels fecal matter.
Common disorders include hemorrhoidal vascular cushions, anal fissures, and infectious lesions. Hemorrhoids present as dilated veins prone to bleeding and prolapse. Fissures appear as linear mucosal tears causing sharp pain. Bacterial or viral infections may generate erythema, discharge, and ulceration.
Ectoparasites can affect the perianal skin. Typical agents and their impacts are:
- Ticks: attach to skin, feed on blood, may transmit bacterial or viral pathogens.
- Bugs (e.g., bedbugs): bite, induce localized swelling and itching.
- Lice: crawl on hair and skin, cause irritation and secondary infection.
- Fleas: bite, provoke pruritus and possible allergic reactions.
Infestation often leads to inflammation, secondary bacterial infection, and discomfort during toileting. Prompt removal and topical or systemic treatment reduce complications and restore normal function of the rectal outlet.