The Male Anatomy

For many people, talking about the penis is tough. This area of the body is considered private and is usually not discussed publicly. However, the penis is simply a part of the male anatomy designed to accomplish a task, and we'll treat it that way here.

In the case of the penis, there are actually two tasks that it handles:

1. releasing urine from the bladder, known as urination
2. releasing sperm and seminal fluid from the prostate gland, known as ejaculation

Viagra® helps with the second task: ejaculation.

When things are working properly, ejaculation is a three-step process:

1. The man becomes sexually aroused.
2. The penis responds by becoming erect.
3. Stimulation of the penis causes ejaculation.

That sounds simple enough, but in many cases, step two does not happen, making step three difficult or impossible. Although the man is stimulated, the penis does not become erect. To understand why, you need to understand the technology of an erection.

When you want to move nearly any part of your body, you do it using muscles. Whether you are moving your fingers, toes, arms or legs, muscles do the work. Even when you stick your tongue out, you do it using muscles:

• You think about moving some part of your body
• The appropriate muscles contract
• That part of the body moves

Muscles let you move your body voluntarily with precise control.

The penis, on the other hand, is completely different. There are no muscle contractions involved in making the penis erect. To become erect, the penis instead uses pressure.

Probably the easiest way to understand how the penis becomes erect is to think about a balloon. If a balloon has no air in it, it is limp. As you inflate a limp balloon with just a little air, it becomes elongated and rigid.

The penis uses a similar mechanism, but instead of using pressurized air to become rigid, the penis uses pressurized blood. The penis contains two cigar-shaped structures, called corpora cavernosa (singular - corpus cavernosum), that it uses to become erect.

Think of the corpora cavernosa as balloon-like tubes. Arteries bring blood into these two tubes, and veins carry blood away from them. The penis can be either limp or erect, depending on the flow of blood:

• In a non-erect state, the arteries that bring blood into the corpora cavernosa are somewhat constricted, while the veins that drain the blood from the penis are open. There is no way for pressure to build inside the penis. In this state, the penis is limp.

• When a man becomes aroused, the arteries leading into the penis open up so that pressurized blood can enter the penis quickly. The veins leaving the penis constrict. Pressurized blood is trapped in the corpora cavernosa, and this blood causes the penis to elongate and stiffen. The penis is erect.

If the arteries leading to the penis do not open up properly, it is difficult or impossible for a man to become erect. This problem is the leading cause of erectile dysfunction (ED).

To solve an erection problem when the cause is poor blood flow, you need to open the arteries. Let's take a look at how this can be done -- and how it was done before Viagra.

Early Treatments for ED

The first real breakthrough in the treatment of erectile dysfunction came in 1983. Prior to that time, it was thought that erectile dysfunction -- the inability to achieve an erection -- was primarily mental. That concept came crashing down at the 1983 American Urological Association meeting in Las Vegas when Dr. Giles Brindley injected his penis with the drug phentolamine. Following the injection, Dr. Brindley appeared on stage and dropped his pants to display one of the first drug-induced erections to the incredulous audience of urologists.

What did the phentolamine do? It relaxed a muscle. Here's how: Inside the body there are several kinds of muscle:

• Skeletal - Skeletal muscles are the muscles we see at the Olympics -- bulging biceps and so on.
• Cardiac - Cardiac muscle powers the heart.
• Smooth - Smooth muscle can be found in things like blood vessels, the intestines and the stomach and usually acts involuntarily.

Smooth muscle plays a key role in every erection. See How Muscles Work for details.

Smooth muscle plays a key role in every erection, and Phentolamine is a drug that relaxes smooth muscle.

The reason why an injection of phentolamine gave Brindley an erection was especially interesting in 1983 because no one had really thought about it before. Here's what happened:

• The arteries of a limp penis are constricted, and they keep blood from entering the corpora cavernosa.

• Brindley's injection relaxed the smooth muscle in the artery walls inside his penis, causing them to open up.

• Blood surged into the corpora cavernosa, and the blood pressure inflated his penis, giving him an instant erection.

Starting in the mid-1980s, it became common for men with erectile dysfunction to inject smooth-muscle-relaxing drugs as a treatment for the problem.

Viagra® makes the process a whole lot easier by doing the same kind of thing with a pill instead of an injection. Another advantage of Viagra® over an injection of phentolamine is that Viagra® only causes an erection when the man is sexually aroused. Phentolamine, by contrast, causes an immediate and uncontrolled erection.

How can a pill work only on the smooth muscle in the penis and not the entire body, and only when the man is aroused? The answers to these questions begin with an understanding of how blood flow works in the body, so let's start there.