Erection (in Latin – to raise, stand upright) is one of the phases of sexual intercourse. It can be caused by central stimuli that are produced by the brain or local sensory stimulation of the genitals.
The physiological mechanism of penile erection development involves several consecutive phases:
Increase in parasympathetic activity
Release of nitric oxide (NO) in cavernous body
Increase in concentration of cyclic guanosine monophosphate (cGMP)
Relaxation of smooth muscle cells of the penis
Increase of blood flow to cavernous body
Compression of venules and blocking of the blood outflow from the penis.
Erection of the penis is caused in response to a variety of stimuli arising from erotic fantasies or direct physical stimulation of the penis. In response to sexual stimuli, the cavernous and spiral arteries of the penis expand, and additional blood flow begins to flow to them.
Cavernous and spongy bodies are supplied with the blood along the deep artery and along the dorsal artery of the penis. Increase in the volume of cavernous body causes compression of the venules and blocks the blood outflow from the penis.
One of the hormones that regulates process of erection occurrence is testosterone. Its normal level in the blood contributes to launch of the mechanism of erection, as well as determines degree of sexual arousal and libido.