What Causes an Erection?
What causes an erection? Many chemical interactions occur between the time a man begins to get sexually aroused and when he achieves an erection. Basically, erection begins when a man is sexually stimulated, which can be physical (e.g., kissing, touching the penis) or mental (e.g., sexual fantasies). The sexual stimulation triggers the brain to send electrical impulses to the penis along nerve fibers.
What Causes an Erection? The Mechanics
Nerve cells in the corpora cavernosa, two spongy tubes in the penis, begin to produce nitric oxide, which stimulates an enzyme called guanylate cyclase. This enzyme transforms a chemical called GTP into yet another chemical called cyclic guanosine monophosphate (cGMP). The cGMP causes smooth muscle in the arteries to relax, which allows blood flow to the penis to increase. The veins that carry the blood away close up, or constrict, which traps the pressurized blood in the corpora cavernosa. The result is an erection.
Part of this sequence involves yet another chemical called PDE (phosphodiesterase), which breaks down cGMP and turns it back into GTP. When the supply of cGMP is interrupted, an erection cannot occur.
One of the most common reasons a man develops erectile dysfunction is that the arteries in the penis do not dilate enough when they receive the signals. Although nitric oxide is produced, there is not enough cGMP to maintain an erection. Men who have this situation need something that increases blood flow to the penis, and that is what the major ED drugs can do. When a man takes an erectile dysfunction drug, it enters the bloodstream and targets the PDE5 enzyme in the penis. Once the drug attaches to the PDE5 enzyme, it disables most of it, which means it can no longer break down cGMP. This allows cGMP to accumulate in the penis: the more cGMP a man has, the greater the blood flow, and thus the better the erection Read more on how ED drugs work.
What Causes an Erection? The 4-Hour Erection
The advertisements on TV for the major ED drugs always advise you to “seek medical attention if you have an erection lasting longer than 4-hours”. One side effect from drugs to treat ED can be a prolonged erection (known as priapism; an erection lasting longer than four hours). A prolonged erection may also be caused by other treatments such as injections and MUSE suppositories.
Priapism is a serious medical condition, because the penis is deprived of oxygen, which damages and destroys erectile tissue. Thus medical attention should be sought immediately. Often times, your doctor may give you an information card similar to the Sloan-Kettering Wallet Card for patients using penile injections. This card details the serious nature of priapism and advises the attending medical professional of treatment options and other information.
