How Viagra Works ?

Viagra Wiki — Tue, 17 Nov 2009 05:19:28 +0000

To understand how to make a penis-specific drug, think about the way blood flows in your body. Your body has just one pump — the heart. But different parts of the body need different amounts of blood at different times.

For example:

If you eat a big meal, your body needs to send more blood to the stomach and intestines to help with digestion.
If you are running in a marathon, your body needs to send more blood to your arm and leg muscles, and it may want to cut most of the blood flowing to the stomach (and other nonessential organs) in order to save oxygen for the legs.

What your body needs, in other words, is a set of valves that it can use to increase and decrease blood flow to certain parts of the body. And your brain needs a way to control those valves so it can turn them on and off when necessary.

The penis is one of the places in the body where the brain needs to be able to turn the blood flow on and off with a valve. To understand how the brain controls this particular valve, let’s start with the basic concept at work: How does the brain control blood flow to different parts of the body?

Turning Valves On and Off
In the human body, the “valves” open and close using muscles in the walls of arteries. When these muscles relax, the arteries open up and blood flow increases. The valves respond to chemical messages that the brain can control.

The mechanism that the body uses to “open a valve” in any part of the body involves four steps:

The brain sends a signal down a particular nerve fiber. This nerve fiber ends in an NANC nerve cell in an artery, somewhere near the point where blood flow needs to change. NANC stands for nonadrenergic-noncholinergic, and what it means is that the NANC nerve cell is able to create nitric oxide.
The NANC nerve endings inject nitric oxide into the blood and surrounding cells.
The nitric oxide stimulates an enzyme called guanylate cyclase in nearby cells, and this enzyme starts producing a chemical called cyclic guanosine monophosphate (cGMP).
cGMP tells smooth muscles that line an artery to relax. When they relax, blood flow increases.

This mechanism is a simple little chemical machine, and the brain uses it to increase blood flow in several different parts of the body. But there is one final part to this chemical machine: Another enzyme called phosphodiesterase (PDE) deactivates the cGMP.

The brain sends signals to NANC cells in the artery. The NANC cells release nitric oxide (NO). Nitric oxide acts as a signaling molecule and stimulates an enzyme called guanylate cyclase in nearby cells. The guanylate cyclase converts a chemical called GTP into another chemical called cGMP. cGMP causes muscles in the walls of the arteries to relax. This relaxation increases blood flow. Meanwhile, PDE is decomposing the cGMP and turning it back into GTP. There is a cycle — guanylate cyclase turns GTP into cGMP, and PDE turns cGMP into GTP. Nitric oxide turns the cycle on.

cGMP is produced as long as the brain is sending messages down the nerve fibers in the artery, which generate nitric oxide and keep the cycle going. When the brain stops sending the signal, all of the cGMP goes away because PDE is deactivating it. This way, the brain can turn valves on and off whenever it wants to.

So how does this relate to an erection?

When the brain gets aroused, it sends a signal to the penis. Nerve cells in the penis’ corpora cavernosa start producing nitric oxide, which leads to the creation of cGMP. The cGMP causes arteries in the corpora cavernosa to dilate, causing lots of blood to flow into the penis. The extra blood flowing in causes the penis to inflate like a balloon. An erection occurs.

When a man suffers from erectile dysfunction, there can be many reasons for the problem. But one of the most common reasons, especially in older men, is that the arteries in the penis aren’t dilating enough when the brain sends the signal. The man is aroused, and the nerves in the penis are producing NO; but the amount of cGMP produced is not enough to maintain an erection.

The way that Viagra goes about solving this problem is quite ingenious, and involves the following question: How can you create a drug that affects only the penile valve?

If you want to create a drug that increases blood flow to the penis, there are at least three ways to do it:

Increase the amount of nitric oxide produced in the penis
Increase the amount of cGMP produced in the penis in response to the nitric oxide
Eliminate the PDE in the penis so that the cGMP builds up instead of getting decomposed by the PDE

Viagra uses method No. 3 — it eliminates the PDE that is decomposing the cGMP, so cGMP builds up in the penis and has a larger effect on the artery walls. The greater the amount of cGMP the greater the blood flow, and the greater the blood flow the greater the degree of the erection.

The reason that Viagra uses this technique is because of an interesting quirk of PDE.

It turns out that the human body has at least 11 different kinds of PDE that it produces. Only one of those kinds of PDE — PDE5 — is found primarily in the penis. Once scientists discovered this fact, the creation of Viagra®was relatively simple. All that Pfizer needed to find was a chemical that would selectively block PDE5 and nothing else. With the PDE5 blocked, cGMP could build up in the penis and increase the blood flow there without affecting other parts of the body.

How the Penis Erection ?

Viagra Wiki — Tue, 17 Nov 2009 03:54:57 +0000

The average male has four to eight spontaneous erections every night while he sleeps. They usually occur during the REM stage, when dreaming is most common.

When a doctor wants to know whether a patient’s difficulty achieving an erection is due to physical or mental reasons, one way to find out is to fit the patient’s penis with a sensor and see whether or not the patient’s dream erections are working properly. If not, the problem is probably physical.

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

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

That sounds simple enough, but in many cases, step two doesn’t happen, making step three difficult or impossible. Although the man is stimulated, the penis doesn’t 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’s 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 balloonlike 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 don’t 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.

Erectile dysfunction and ED Treatment » Erection

How Viagra Works ?

How the Penis Erection ?