HEMORRHOIDS: ANATOMY

A little anatomy

Defecation, or the elimination of faeces from the body, occurs thanks to a mechanism that is only partially involuntary. The opening of the anus is in fact controlled by a muscular apparatus, called the anal sphincter, and by a submucosal vascular pad.

The anal sphincter consists of an involuntary upper part, which relaxes in the presence of stools causing the simultaneous contraction of the "outermost ring. The opening of this second sphincter is voluntary, that is controlled by the subject through a series of contractions and maneuvers." which have the purpose of favoring the evacuation of faeces (see: Valsalva maneuver).

The vascular cushion that ensures the nutrition and oxygenation of these important structures is formed by an intricate system of arterial and venous vessels which together constitute the hemorrhoidal plexus.

The main veins that branch off from this area are called haemorrhoidal veins and together with the other vessels have the important function of contributing to the maintenance of continence, deflating at the physiological action and vice versa.

As is often the case with the veins of the lower limbs, the hemorrhoidal plexus is also subject to varicose veins. These changes in 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 haemorrhoidal pathology (see figure). Depending on whether the pathology affects the submucosal or subcutaneous hemorrhoidal plexus, we speak of internal and external hemorrhoids respectively.