The rectal ampulla is a dilation of the last part of the large intestine, called the rectum and predisposed to the accumulation and excretion of faeces. This canal is about 12-14 centimeters long and shows a non-uniform caliber: in many sections it is similar to that of the colon, but in the initial portion, after a short constriction, it presents a pyroid dilation with a lower base, known precisely as the rectal ampulla ( endopelvic rectum). At this level the faeces accumulate, waiting for the stimulus to evacuate; this, not surprisingly, is triggered precisely by a "suitable distension" of the ampoule itself.
Below the pelvic diaphragm we find the perineal part of the rectum, more restricted and called the anal canal, which ends in the anus. The limit between the two parts, the upper one located in the pelvis, and the anal canal inferiorly in the perineum, is given by the "insertion on the rectal wall of the levator ani muscle which, as the name suggests, by contracting lifts the rectum and anus contributing to its continence.
In the rectum the secretion and absorption functions are of little importance and the modest quantity of secreted mucus has the purpose of lubricating the faeces for easier expulsion; Basically, therefore, the rectum has the function of continence (rectal ampulla) and defecation.
The angle between the rectal ampulla and the anal canal is about 80-90 ° and this contributes to the continence capacity of the individual; during the flexion of the thighs beyond 90 °, as well as during defecation, the angle between the rectal ampulla and the anal canal increases (therefore the two segments are more "aligned"); this is the reason why the most physiological position for defecation it is the crouching one (Turkish style), in which the abdomen is naturally compressed against the thighs (a useful remedy in the presence of constipation is to place a rise under the feet near the toilet).
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