What is an erection?
Erection is the ability to achieve and maintain sufficient rigidity of the penis for a successful start and completion of the sexual intercourse.
The penis is composed of two paralel corpora cavernosa and a third, narrower, corpus spongiosum that surrounds the penile urethra and shapes the head of the penis (glans penis). The corpora cavernosa consist of spongy tissue that is surrounded by a thick sheath (tunica albuginea). Specialised mechanisms regulate the inflow and outflow of blood in the corpora cavernosa, enabling the penis to fill up with blood very quickly , swell and become rigid – this is called an erection.