Читать книгу Pathy's Principles and Practice of Geriatric Medicine - Группа авторов - Страница 483

As stool is passed into the rectum by peristalsis, the rectal pressure increases, and the internal anal sphincter pressure constricts and then relaxes. A small quantity of rectal contents is passed into the anal canal, where the composition of the stool – solid, liquid, or gaseous – is assessed by sensory receptors in the anal epithelium.¹³ If convenient and socially appropriate, once the individual has reached appropriate facilities and disrobed, the process of defecation begins. A seated or squatting position straightens the anorectal angle to ease the passage of stool.¹⁴ The pelvic floor is relaxed, and there is an involuntary increase in colorectal motor activity combined with a voluntary Valsalva manoeuvre, which leads to rectal pressure being higher than anal pressure, allowing stool to pass. The differential in pressure required to allow the stool to pass is a function of stool consistency, with higher pressure needed to pass hard type 1 stool compared to softer or liquid stool¹⁵; by extension, liquid stool is more difficult to contain.