Physiology of penis


The mechanism is dependent on the ability of the spongy tissue (corpora cavernosa) to become engorged with blood, usually arterial blood. This is caused by the contraction of the ischiocavernosus which assists the closure of the drainage pathway of the arteries. Also, it is believed there is a concomitant venoconstriction which helps to keep blood within the spongy tissues of the penis. This mechanism is released after the arousal has passed so that the organ becomes flaccid again. It is only in man amongst all mammals that a bone of the penis does not exist as a form of platform for the erectile mechanism of the organ. This bone is called os penis.

The peripheral function of erection has been studied recently and it involves the release of neurotransmitters from endothelial cells of the penis which then relaxes smooth muscle in the arteries, arterioles and erectile tissue trabeculae (corpora cavernosa and corpus spongiosum) of the penis and which helps to fill up the erectile tissue with blood and also the sinusoids with expansion of erectile tissues. The venous plexus  which drains the penis then becomes compressed by these events leading to almost complete blockage of venous outflow form the penis. cGMP is the second messenger in this pathway for the action of the principal neurotransmitter of the penile erectile action -nitric oxide. cGMP action is terminated by the isoenzyme phosophodiesterase type 5 (PDE5).

The penis is also responsible for the second stage of ejaculation which involves the emptying of the urethra by the assistance of the bulbospongiosus.


Male sexual arousal

Male sexual climax

Mechanism of erection



Erectile dysfunctions

Sexual dysfunctions


Penis; cross section
Penis and scotum Dissected penis Parts of penis Perineum and scrotum from behind Scrotum from behind

Circumcised  penis Uncircumcised penis anatomy Structure of penis Fresh penis Variations



Inflation and deflation of penile implant








Gross anatomy
Lymphatic drainage
Organ integration
Clinical anatomy





Chemical Pathology

Anatomical Pathology






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Creator: Oluwole Ogunranti