The rectal ampulla is a dilation of the last tract of large intestine, called rectum and predisposed to the accumulation and excretion of feces. This channel is about 12-14 centimeters long and shows an uneven caliber: for many traits it is similar to that of the colon, but in the initial portion, after a short throttling, it presents a pyro-dilation with a lower base, known as rectal ampulla ( endopelvic rectum). At this level the feces accumulate, waiting for the stimulus to evacuate; this, not surprisingly, is triggered by a suitable distension of the ampoule itself.
Below the pelvic diaphragm we find the perineal part of the rectum, narrower and called the anal canal, ending in the anus. The boundary between the two parts, the upper part 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, contracts and raises the rectum ano contributing to his continence.
In the rectum the functions of secretion and absorption have little importance and the modest quantity of secreted mucus has the purpose of lubricating the feces for an easier expulsion; fundamentally, therefore, the rectum has the function of continence (rectal ampulla) and defecation.
The angulation between the rectal ampulla and the anal canal is about 80-90 ° and this contributes to the individual's ability to continence; during the flexing 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 to defecation is the crouched (Turkish), 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 in proximity of the wc).
