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The internal anal sphincter, IAS, or sphincter ani internus is a ring of smooth muscle that surrounds about 2.5–4.0 cm of the anal canal. It is about 5 mm thick, and is formed by an aggregation of the smooth (involuntary) circular muscle fibers of the rectum. It terminates distally about 6 mm from the anal orifice. [citation needed]
The internal sphincter is a continuation of the detrusor muscle and is made of smooth muscle, therefore it is under involuntary or autonomic control. This is the primary muscle for prohibiting the release of urine. The female or male external sphincter muscle of urethra (sphincter urethrae): located in the deep perineal pouch, at the bladder's ...
Scar tissue is removed and the mucosa of the anal canal separated from the damaged sphincter. The sphincter is cut and its ends overlapped and then stitched back together. The exact method of the procedure varies, e.g. the cut sphincter may be stitched back end to end, rather than overlapped, or the IAS and EAS may be repaired as separate stages.
Nontraumatic conditions causing anal sphincter weakness include scleroderma, damage to the pudendal nerves, and IAS degeneration of unknown cause. [5] Radiation-induced FI may involve the anal canal as well as the rectum, when proctitis, anal fistula formation, and diminished function of internal and external sphincter occur. [2]
The internal urethral sphincter is a urethral sphincter muscle which constricts the internal urethral orifice. It is located at the junction of the urethra with the urinary bladder and is continuous with the detrusor muscle, [1][2] but anatomically and functionally fully independent from it. [3] It is composed of smooth muscle, so it is under ...
Proctalgia fugax. Specialty. General surgery. Proctalgia fugax, a variant of levator ani syndrome, is a severe, episodic pain in the regions of the rectum and anus. [1] It can be caused by cramping of the levator ani muscle, particularly in the pubococcygeal part. [2]
Perineal tear. A perineal tear is a laceration of the skin and other soft tissue structures which, in women, separate the vagina from the anus. Perineal tears mainly occur in women as a result of vaginal childbirth, which strains the perineum. It is the most common form of obstetric injury. [1]
Lateral internal sphincterotomy is an operation performed on the internal anal sphincter muscle for the treatment of chronic anal fissure. The internal anal sphincter is one of two muscles that comprise the anal sphincter which controls the passage of feces. The procedure helps by lowering the resting pressure of the internal anal sphincter ...