Biomechanically, an erection is a simple two-step process. At the first stage, as a result of relaxation of the SMC, the lumen of the cavernous arteries and sinuses increases, and under the pressure of the incoming blood, the corpora cavernosa expands. At the same time, the penis swells, but this is still not enough to straighten and stiffen it.
The fact is that the blood arriving in the cavernous sinuses is constantly discharged through the circumflex veins. However, with maximum relaxation of the MMC, the incoming blood expands the elastic corpus cavernosum to such an extent that it begins to press the veins against the hard shell of the penis. As a result of cross-clamping of the veins, the discharge of blood from the cavernous sinuses is blocked, therefore, the blood arriving through the arteries is trapped. This is the second stage in the development of an erection, as a result of which the penis reaches its maximum size and rigidity, sufficient for intercourse.
So, an erection develops as a result of the expansion of the arteries bringing blood and the subsequent clamping of the veins. Ok, everything is clear with the vein clamping mechanism, but how is the tone of the SMC arteries regulated?
Regulation of erection
At rest, sympathetic nerve fibers keep the MMC in good shape, so the penis is sluggish. An even stronger tone of SMCs develops when the surface of the body is cooled, which is familiar to every man in the form of a significant decrease in the size of the penis, for example, when swimming in cold water.
There is nothing extraordinary in this, in a similar way the whole body reacts to cold – blood is redistributed to the center of the body from the skin, mucous membranes and all extremities (fingers, nose, penis) to reduce heat loss and prevent general hypothermia. However, even despite the cold, this ancient and important reflex is suppressed by the more dominant one – the sexual one.
An erection develops on a command from the central nervous system (visualization or fantasy) and as a result of mechanical stimulation of the erogenous zones. Both signals intersect at the level of the lowest segments of the spinal cord, from where parasympathetic nerve fibers exit, transmitting the summed signal to the penis.
In the nerve endings of these fibers, nitric oxide (NO) is synthesized from the amino acid arginine, which penetrates into the smooth muscle fiber of the arteries. Here, NO activates an enzyme that converts the GTP nucleotide into cGMP, the accumulation of which causes the relaxation of the SMC of the cavernous arteries and sinuses and their filling with blood.Поділитися цим: