An erection is primarily controlled by the brain, which has long been uncontroversial. Specific centers of the spinal cord control the filling of the penis with blood. It also requires monoxide-nitrogen, a substance formed from the amino acid L-arginine, which relaxes the vascular muscles in the penis, so they expand and 'pump' the penis with blood.
Therefore, all factors negatively affecting the quality of blood vessels can lead to impotence. The "bad" list includes being overweight, high blood pressure, diabetes mellitus, smoking, and, most importantly, stress. Adrenaline and norepinephrine, the well-known stress hormones, are notoriously bad for erections.
Inside the penis are cavernous bodies, along the walls of which there are muscles that can change their size and in which a small amount of blood circulates. When sexually aroused, a powerful impulse is delivered to the genitals, and the muscle fibers in the walls of the arteries and cavernous bodies relax, increasing the blood flow.
Blood fills in all the vessels and ducts, and the firm sheath is palpable under the skin when aroused, pulling on the full-blooded penis. The pressure, in this case, can be compared to pumping up a car tire. The penis becomes hard and visually rushes upwards. Blood entering the venous system of the penis cannot drain as quickly, so the penis remains elastic for a long time.
When the level of sexual arousal decreases, the muscles in the large bodies contract, the blood drains away, and the erection ends. The substance that commands the relaxation of the muscles is called acetylcholine. It is essential to bear in mind that in case of blood clotting disorders, neurological diseases, tumors, and injuries of the penis, as well as taking drugs, a prolonged erection leads to painful sensations and has dangerous consequences that have nothing to do with pleasure.