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 smoot muscle of '''corporal sinusoids''' to relax (vasodilation).
+
* 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.
 +
 
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== 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.

Sensory Input and Local Vascular Response