How Viagra Works

الكاتب : منير الشيخ   المشاهدات : 3,167   الردود : 9    ‏2006-06-20
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  1. منير الشيخ

    منير الشيخ قلم فضي

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    الفياجرا


    هذا الدواء الذي اصبح له مكانه عزيزة وخاصة عند كثير من الرجال التواقين الى تحقيق السعادة الزوجية، هذا الدواء الذي حققت من بعده الشركة الامريكية مبالغ خيالية هائلة. فكيف يعمل هذا الدواء لنرى.​



    Viagra® is one of the best-known drugs of all time:
    Google lists over 17 million Web pages that use the word "Viagra." For comparison, Google lists only 3.3 million pages containing the word "aspirin" and only 936,000 containing the word "Tylenol."
    Billions of spam e-mail messages advertise Viagra® every day. There is so much Viagra spam, in fact, that Pfizer (the maker of Viagra) has a page addressing the problem, called Avoid Fake Viagra: The Facts About Spam, prominently listed on Viagra.com.
    Pfizer has spent untold millions of dollars advertising Viagra®, so you see advertisements for the drug constantly on TV.
    Pfizer claims on its Web site that nine Viagra® pills are dispensed every second -- nearly 300 million tablets per year.
    The name recognition of Viagra® is so good that nearly every adult in America has heard of the drug and can tell you what it does.
    What Viagra® does is simple: When it works as intended, Viagra® causes a man who is sexually stimulated to get an erection.

    How does Viagra® do that? And why does Viagra® work only if the man is sexually stimulated? For that matter, what causes an erection in the first place? In this article, we'll answer all of those questions and more...


    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.

    [​IMG]

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

    releasing urine from the bladder, known as urination
    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:

    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 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.

    [​IMG]

    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.

    [​IMG]


    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.

    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...

    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.

    [​IMG]

    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.

    Opening Things Up
    How can you give a man an erection with a pill? You can't give a man a pill loaded up with a general smooth-muscle relaxer like phentolamine -- that would cause all of the smooth muscle throughout the man's body to relax, and that might create a lot of problems. What you need is a drug that acts only on the smooth muscle in the arteries of the penis.
    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 non-essential 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 bloodflow 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

    [​IMG]

    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?

    The Viagra® Way
    The Nobel Prize
    In 1998, three scientists -- Robert F. Furchgott, Dr. Ferid Murad, and Louis J. Ignarro -- won the Nobel Prize in Physiology or Medicine for showing that nitric oxide acts as a signaling device between cardiovascular cells. See NobelPrize.org: The Nobel Prize in Physiology or Medicine 1998 to learn more.

    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 number three -- 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.

    If there were not a unique type of PDE found in the penis, we would not have Viagra® today.

    So how does Viagra® block PDE5?

    PDE5 is what is known as an enzyme. An enzyme is a specially folded protein that can speed up a chemical reaction. For example, the article How Cells Work describes the maltase enzyme. Maltase is shaped so that a maltose molecule can fit right in, and when it does, the maltase enzyme breaks the maltose molecule into two glucose molecules, as shown here:

    [​IMG]

    PDE5 is an enzyme that accepts cGMP and breaks it down. Pfizer needed a chemical that would gum up PDE5 and keep it from doing its job. The chemical that Pfizer discovered is called sildenafil citrate. It fits right into the PDE5 enzyme and disables it.

    Viagra® contains sildenafil citrate packaged as a pill. When a man takes a Viagra® pill, the sildenafil citrate flows throughout his body, but it really only affects the PDE5 enzyme in the penis. The drug stays in the bloodstream for about four hours, and then it is washed out of the blood by the liver and kidneys.

    And that's the end of the "how it works" part of the Viagra® story:

    A man takes a Viagra® pill.
    The sildenafil citrate enters his bloodstream and flows throughout his body.
    The sildenafil citrate attaches to the PDE5 enzyme in his penis and disables most of it.
    When the man becomes sexually aroused, the brain sends the normal message to the NANC cells in his penis, which produce nitric oxide as usual.
    The nitric oxide creates cGMP, which starts relaxing the arteries in his penis.
    Since the PDE5 has been disabled, the cGMP in the penis does not break down. Instead, it builds up and lets the arteries in the penis fully dilate.
    His penis inflates with blood, and the man gets a full erection.
    This works perfectly for the majority of men, except for a few minor problems


    Side Effects of Viagra®
    Very few drugs work perfectly, and Viagra® is no exception. Just about every drug has side effects that arise because the drug is flowing throughout the body and may affect parts of the body unintentionally. For example, aspirin is a drug that relieves pain, but this same drug can also erode the stomach lining and thin the blood. Those are side effects of aspirin.
    Viagra® has several side effects of which patients need to be aware.

    The first problem comes because Viagra® happens to have a spill-over effect. It blocks PDE5, but it also has an effect on PDE6. It turns out that PDE6 is used in the cone cells in the retina, so Viagra® can have an effect on color vision. Many people who take Viagra® notice a change in the way they perceive green and blue colors, or they see the world with a bluish tinge for several hours. For this reason, pilots cannot take Viagra® within 12 hours of a flight.

    The second problem comes for people who are taking drugs like nitroglycerin for angina. Nitroglycerin works by increasing nitric oxide, and it helps with angina by opening up the arteries that supply the heart with oxygen. If you take nitroglycerin and Viagra® together, the increased nitric oxide plus the blocking of PDE5 can lead to problems.

    Other problems with Viagra® can include little things like headaches (the drug, as a side effect in some men, opens up arteries in the brain's lining and causes excess pressure) and big things like heart attacks. The possibility of heart attacks is one reason why Viagra® is a prescription drug rather than an over-the-counter drug like aspirin. A doctor needs to understand your medical history and make sure that Viagra® won't cause a heart attack. Occasional patients who take Viagra® get painful, long-lasting erections and have to see a doctor to solve the problem.

    Finally, there is some concern that some men, especially younger men who take Viagra® recreationally and who don't really need it for physical reasons, may end up with a dependency on the drug. That is, they may become unable to maintain an erection without taking Viagra®.

    For more information about side effects, see RxList: Viagra® Side Effects.

    What about Cialis® and Levitra®?
    Viagra® is a hugely successful drug, and other drug companies wanted a piece of the action. They developed different chemicals to block the PDE5 enzyme and created two new drugs: Cialis® (tadalafil) and Levitra® (vardenafil).

    Because Cialis® and Levitra® block the PDE5 enzyme, they work exactly the same way as Viagra®. They help men who have trouble maintaining an erection because of blood flow problems, and they only work when the man is sexually aroused.

    Because they block PDE5 with different chemicals, however, there are some important differences between the three drugs. For example:

    Only Viagra® causes color-vision problems.
    Cialis® causes muscle aches in about 5 percent of patients.
    Viagra® and Levitra® last about four hours in the bloodstream. Cialis® stays in the bloodstream much longer (it has a 17.5-hour half life) and can therefore be effective for more than a day​
    .[/LEFT]
     
  2.   مشاركة رقم : 2    ‏2006-06-21
  3. mohammed

    mohammed قلم فضي

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    its was very kool bro but i wanna tryViagra
    but beleive me its the same u know with men young men it doesnt matter


    best wishs
    c u
     
  4.   مشاركة رقم : 3    ‏2006-06-21
  5. mohammed

    mohammed قلم فضي

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    its was very kool bro but i wanna tryViagra
    but beleive me its the same u know with men young men it doesnt matter


    best wishs
    c u
     
  6.   مشاركة رقم : 4    ‏2006-06-25
  7. منير الشيخ

    منير الشيخ قلم فضي

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    thank you for comment
    and as you say it doesnt matter with young men
     
  8.   مشاركة رقم : 5    ‏2006-06-25
  9. أبومطهر

    أبومطهر قلم فضي

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    يا شيخ منير


    موضوعك كوووووووووول

    اتمنى لو تستطيع انزالة بالعربي مرة اخرى

    سلالالالالالالالالالالالالالالالالالالالالالالالالالالالالالام


    العبد الفقير لله


    أ بــــو مــــــــــطــــــــــهـــــــــر
     
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  11. منير الشيخ

    منير الشيخ قلم فضي

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    مشكور ابو مطهر حبيبي

    بس الموضوع افيد باللغ الانجليزية


    لكن اصبر علينا
    وان شاء بايصير خير
     
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  13. منير الشيخ

    منير الشيخ قلم فضي

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    ملخص الكلام يا بو مطهر



    قبل أن نتطرق لتفاصيل عمل الفياجرا يجب أن نتعرف على الجهاز التشريحى للقضيب أو العضو الذكرى .
    فهو عبارة عن شريان دموى كبير ينقسم إلى ثلاثة أجزاء أى ثلاث أنابيب ، الأنبوبة الأمامية تمر فيها قناة مجرى البول الجسم الكهفى للعضو الذكرى وسمى بهذا الإسم لأنه مقسم إلى كهوف لتحتوى الدم القادم من الإنتصاب وأحياناً تسمى و تنتهى برأس القضيب خلفها توجد أنبوبتان متصلتان هما الجسم الإسفنجى لأتها تشبه الإسفنج وهو مقسم إلى كهوف وكل كهف مبطن بخلايا ومحاط بعضلات إذا إنقبضت طردت الدم الموجود بها ويصبح القضيب غير منتصب وإذا إنبسطت فإنها تسمح للكهوف بالإمتلاء بالدم محدثة الإنتصاب وبين الكهف والآحر المجاور له توجد أوردة تقوم بسحب الدم بعد إنتهاء العملية الجنسية إلى خارج العضو الذكرى ، وعندما تمتلئ الكهوف بالدم فإنها تضغط على الأوردة وتغلقها وإذا لم تنجح فى إغلاقها تسرب الدم إلى هذه الأوردة ومنها إلى الدورة الدموية مما يؤدى إلى ضعف الإنتصاب .
    ومع الإثارة الجنسية يفرز الجسم مادة أكسيد النيترات الذى يقوم لتحويل مادة كيميائية ثلاثية الفوسفات إلى مادة كيميائية أحادية الفوسفات والأخيرة ( أحادية الفوسفات ) تؤدى إلى إنبساط العضلات المحيطة بالكهوف مما يساعد على امتلائها بالدم محدثة الإنتصاب ، ثم تتكسر هذه المادة أحادية الفوسفات بفعل انزيم معين لتتحول إلى مادة غير فعالة فلا يحدث الإنتصاب لفترات طويلة جداً مما يتعارض مع آلية العملية الجنسية ، ولكن بعض الأشخاص ينشط لديهم هذا الإنزيم بطريقة غير طبيعية مما يضعف من عمل المادة الكيميائية أحادية الفوسفات وبالتالى ضعف عملية الإنتصاب .
    ومن هنا تأتى أهمية الفياجرا لأنها تكسر هذا الإنزيم النشط وتحافظ على فعالية هذه المادة الكيميائية أحادية الفوسفات .
    وينصح الأطباء بتناول الفياجرا على معدة غير ممتلئة وقبل الجماع بساعة ولا يجب أن تؤخذ مع أدوية تحتوى على نيترات لأن هذه النيترات تُخفض ضغط الدم فإذا إجتمعت الفياجرا وأدوية أخرى بها نيترات فإن الضغط قد ينخفض ويسبب متاعب صحية للإنسان .
     
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  15. مجنون اونلاين

    مجنون اونلاين عضو فعّال

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    موضوع جميل يا دكتور منير

    مابلا تزوجت ولا زد شفناك فتحت موضوع المكتبه وهربه!!!

    فهل لهذا دخل بذاك؟؟؟
    امزح معك!!!
    كن بخير والسلام عليكم ورحمة الله
     
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  17. منير الشيخ

    منير الشيخ قلم فضي

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    اخي الحبيب مجنون اون لاين


    كلما كنت اطالع مواضيعك وردودك كنت اتمنى ان يكون اسمك لا اسمي على موضوع المكتبة الطبية.


    وانا اعطيك كل الصلاحية والموافقة على نقل الموضوع باسمك فانت فعلا من احياء هذه الفكرة وكل الفظل يعود لك فقط.
     
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  19. مجنون اونلاين

    مجنون اونلاين عضو فعّال

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    أخي الحبيب
    بل الفضل للمتقدم !!!
    إنما فقط كنت استفسر عن غيابك في العسل !!
    كن بخير والسلام عليك ورحمة الله وبركاته
     

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