For you to understand how Viagra, Cialis, Levitra and natural viagra alternatives function, its useful to know the biological mechanisms that cause and maintain erection.

... So How Do I Get An Erection?

As you know, an erection happens when the penis fills with blood and becomes rigid. And that this results mainly as the outcome of mental or physical erotic stimulation or expectation.

Your Penis - A Litle Bit Of Biology

Your penis contains two chambers which run the length of the top of the penis, which are filled with a spongy tissue. These two chambers are known collectively as the corpora cavernosa.

The spongy tissue of the corpora cavernosa is composed of smooth muscles, veins and arteries, small caverties - known as lecuna spaces - and fibrous tissue.

Encasing the corpora cavernosa is a fibrous membrane called the tunica albuginea.

Underneath the corpora cavernosa runs the urethra, which - as its main function - channels urine from the body but which also, during ejaculation, has the additional function of transporting seminal fluid and sperm.

There is also a third chamber, the corpus spongiosum, which surrounds the urethra.

The Physiology Of An Erection

When erotic sensory and mental excitation occurs:

  • The brain and local nervous system (specifically the parasympathetic nervous system) produce impulses.
  • These impulses influence various biochemical processes to cause the smooth muscle of the corpora cavernosa to relax.
  • When this muscle relaxes blood fills the lecuna spaces.
  • When this happens the corpora cavernosa starts to press against the tunica albuginia.
  • Pressure on the tunica albuginia causes it to trap the blood now in the corpora cavernosa.
  • As the blood pressurises the corpora cavernosa the penis grows in size and becomes hard.
  • In trapping the blood the tunica albuginia serves to restrict blood flow out of the penis, thus maintaining erection.

    This process is known as the corporal veno-occlusive mechanism.

    Erection? Its All Down To Biochemical Processes

    The important thing to grasp in all of this is that whilst gaining and maintaining an erection, the tissues of your penis are subject to many different chemical processes involving a number of chemical compounds.

    Amongst these many chemical compounds, taking the major roles are:

  • Nitrous Oxide
  • The enzyme guanylate cyclase
  • guanosine tryphosphate
  • cyclic guanosine monophosphate

    • The Important Role Of Nitrous Oxide

    Since the late 1990s medical research into erectile dysfunction has established that Nitrous Oxide plays a huge role in the mechanism of getting and maintaining an erection

    Researchers are also learning that Nitrous Oxide probably interacts in more than one way with the various other compounds in the process.

    Most important and most studied of these interactions (from the perspective of how Viagra and most other erectile dysfunction drugs work) is that of Nitrous Oxide and its interaction with Guanylate Cyclase and the events that follow.

    A Cascade Of Biochemical Events Leading To Erection

    The process (called by scientists 'the cascade' of events) of getting an erection, works in part like this.

  • Erotic stimulation results in the parasympathetic nervous system triggering the release of large amounts of Nitrous Oxide.
  • This binds to receptors on the enzyme guanylate cyclase.
  • Which in turn causes guanosine triphosphate in the smooth muscle of the corpora cavernosa to be converted to cyclic guanosine monophosphate
  • which in its turn, by means of subsequent biochemical events, causes the smooth muscle of the corpora cavernosa to relax
  • allowing the lecuna spaces to fill with blood and an erection to occur.

    What's This Got To Do With Viagra?

    The action of the last compound in this chain of reactions, cyclic guanosine monophosphate, turns out to be central to the way Sildenafil Citrate (the active component of Viagra) works as we'll see later.

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