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.

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.

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.

Erection of the penis requires:

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.

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.

Flaccid Penis

Erect Penis