Difference between revisions of "Erection - Anatomy & Physiology"
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* NO activates the enzyme guanylate cyclase. | * NO activates the enzyme guanylate cyclase. | ||
* Guanylate cyclase converts guanylate triphosphate (GTP) into cyclic guanyosine monophosphate (cGMP). | * Guanylate cyclase converts guanylate triphosphate (GTP) into cyclic guanyosine monophosphate (cGMP). | ||
| − | * Causes | + | * Causes smooth muscle of '''corporal sinusoids''' to relax (vasodilation). |
* '''Cavernous sinusoids''' engorge with blood. | * '''Cavernous sinusoids''' engorge with blood. | ||
* Intracorporal pressure increases dramatically. | * Intracorporal pressure increases dramatically. | ||
* Pressure compresses the venules through which blood exits the penis. | * Pressure compresses the venules through which blood exits the penis. | ||
* Blood trapped within the penis causing an erection. | * Blood trapped within the penis causing an erection. | ||
| + | |||
---- | ---- | ||
== Sensory Input and Local Vascular Response == | == Sensory Input and Local Vascular Response == | ||
Revision as of 10:25, 10 July 2008
Introduction
- When sexual receptivity of the female is established and sufficient arousal is accomplished in the male, erection and protrusion of the penis ensue.
- Successful penile erection requires a complex series of neural and vasomotor reactions.
- Erection of the penis is necessary for copulation and deposition of semen in the female reproductive tract.
- Erection is characterized by a marked increase in rigidity of the penis.
- Increased rigidity is the result of increase in arterial inflow of blood compared to venous outflow.
- Erection requires that blood be trapped within the cavernous sinus of the penis.
- Increased blood flow to the penis is brought about by vasodilation of the arterioles supplying it.
Erection of the Fibroelastic Penis
- Bull,Ram and Boar
- Involves increased blood flow with subsequent increase in pressure and simultaneous relaxation of the retractor penis muscles.
- Erection and protrusion involve straightening of the penis to eliminate the sigmoid flexure.
- Does not increase significantly in diameter during erection.
Erection of the Musculovascular Penis
- Stallion
- Increases in diameter during erection.
- Retractor penis muscle still relaxes during erection, but no sigmoid flexure.
- Engorgement with blood plays a significant role in the highly vascular penis.
Mechanism
Erection of the penis requires:
- Elevated arterial inflow
- Dilation of corporal sinusoids
- Restricted venous outflow
- Elevated intrapenile pressure
- Relaxation of retractor penis muscles
- Engorgement of cavernous sinuses causes a blockage of venous circulation from the penis.
- Contractions of ischiocavernous muscles cause compression of the penile veins.
- Intermittent contractions of the muscles around the two crura create a pump-like action at the base of the penis.
- Result in the build up of blood within the corpus cavernosum.
- Very high pressure results.
Vascular and Biochemical Control of Erection
Anatomy
- Shaft of the Penis consists of two dorso-lateral corpora cavernosa and the corpus spongiosum.
- Arterial blood is supplied by the internal pudendal artery that supplies dorsal and deep cavernosal arteries.
- Corporal sinusoids are supplied by helicine arteries.
- Deep dorsal vein and superficial dorsal vein drain the erectile tissues.
- For more information on anatomy of the penis follow this link.
Flaccid Penis
- Sinusoids are flattened because adrenergic nerves secrete noradrenaline (norepinephrine)that causes vasoconstriction.
- Blood flow to cavernous tissue is low.
- No eretogenic stimuli present
- Nonadrenergic noncholinergic (NANC) parasympathetic neurons do not fire.
- No release of Nitric Oxide (NO)
- Vasoconstriction takes precedence over vasodilation.
Erect Penis
- Eretogenic stimuli present
- NANC neurones fire and release NO from their terminals.
- NO activates the enzyme guanylate cyclase.
- Guanylate cyclase converts guanylate triphosphate (GTP) into cyclic guanyosine monophosphate (cGMP).
- Causes smooth muscle of corporal sinusoids to relax (vasodilation).
- Cavernous sinusoids engorge with blood.
- Intracorporal pressure increases dramatically.
- Pressure compresses the venules through which blood exits the penis.
- Blood trapped within the penis causing an erection.