To truly understand ED, it’s helpful to know a little about the mechanics of an erection, which usually begins in the brain with feelings of sexual desire. These feelings trigger the release of nitric oxide, a neurotransmitter that sets in motion a relaxation of muscles and allows increased blood flow to the penis.
Breaking these steps down a bit further, we find that the nitric oxide released by the brain in response to feelings of sexual desire sets in motion a chain of chemical reactions that eventually results in an erection. When the nitric oxide reaches the bundle of nerves and blood vessels surrounding the prostate gland, it prompts the guanylate cyclase enzyme to produce cyclic guanosine monophosphate (cGMP), which controls the expansion and contraction of blood vessels that supply the penis. This release of cGMP temporarily expands the arteries that supply the penis and contracts the blood vessels that carry blood away from the penis. This results in an erection.
Also present in the body is the phosphodiesterase-5 enzyme, which under normal conditions breaks down cGMP after an erection. However, sometimes its presence prematurely interferes with the erection process. PDE5 inhibitors temporarily block the effect of the enzyme, which facilitates erection.