Erection - Anatomy & Physiology

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.

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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.

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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.

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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.

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