A little anatomy
Defecation, or elimination of faeces from the body, takes place thanks to a mechanism that is only partially involuntary. The opening of the anus is in fact controlled by a muscular apparatus, called anal sphincter, and by a submucosal vascular pad.
The anal sphincter is made up of an involuntary upper part, which in the presence of faeces relaxes causing the simultaneous contraction of the outer ring. The opening of this second sphincter is voluntary, that is controlled by the subject through a series of contractions and maneuvers that have the purpose of favoring the evacuation of the feces (see: Valsalva maneuver).
The vascular pad that ensures the nutrition and oxygenation of these important structures is formed by an intricate system of arterial and venous vessels that together constitute the haemorrhoidal plexus.
The main veins that depart from this area are called hemorrhoidal veins and together with the other vessels they have the important function of contributing to the maintenance of continence, deflating at the physiological act and vice versa.
As often happens with the veins in the lower limbs, the haemorrhoidal plexus is also subject to varicose veins. These alterations of the tone of the vessel wall, more commonly known as varicose veins, are responsible for the formation of the typical nodular enlargements at the base of the hemorrhoidal pathology (see figure). Depending on whether the pathology affects the submucosal or subcutaneous haemorrhoidal plexus, one speaks respectively of internal and external hemorrhoids.
