What makes the penis get hard, is the engorging of the corpora cavernosa with blood. The penis must fill with blood and trap it with out releasing it. Men with erectile dysfunction either can’t fill their penis with blood, they can’t trap it allowing it to leak out, or there is a problem that it can not store the blood. Regardless of the specific issue, the general problem is blood flow.
You can see from the diagram that when the penis fills with blood it gets bigger. The purpose is so that it can be inserted into the Vagina. It is very difficult for most men to insert his flaccid penis into a women’s vagina.
The penis has two major internal divisions, each responsible for a different function. The corpora cavernosa, which can be likened to hydraulic cylinders, create structural rigidity. The corpus spongiosum contains the urethra, or excretory channel.
The corpora cavernosa are cigar-shaped tubes of strong connective tissue, filled with spongy muscle-lined cavities. Relaxation of vascular muscle causes inflow of blood and expansion of the corpora’s inner sponge during erection. As a result its wall, the tunica albuginea, is stretched tightly enough to produce rigidity. In addition to defining the shape of the erect penis, the tunica also has a key role in limiting blood outflow during erection.
An intracavernous injection, according to the American Urologic Association, is the most effective non-surgical treatment for ED. Injections into the penis, unlike oral medications, trigger an automatic erection. Injection can be done by the individual 5 minutes prior to sexual activity and should last for no more than 1 hour. Injection is considered second line to be used if oral therapy fails. Compounds that can be injected include alprostadil, papaverine, and phentolamine. Alprostadil and phentolamine are the most common agents used as monotherapy. However, combination therapies are used to increase efficacy and decrease side effects. Combination therapy includes Tri-Mix and Bi-Mix. Both products are not commercially available and must be compounded by specialty pharmacies.