What is erection & how it happens?

Penile erection depends on a complex interaction of psychological, neural, vascular and endocrine factors. The pituitary glans, the prostrate and testosterone all have an important role in this process.An erection of the penis occurs when two tubular structures that run the length of the penis, the corpora cavernosa, become engorged with venous blood. This may result from any of various stimuli. The corpus spongiosum is a single tubular structure located just below the corpora cavernosa, which contains the urethra, through which urine and semen pass during urination and ejaculation, respectively. This may also become slightly engorged with blood, but less so than the corpora cavernosa. Penile erection usually results from sexual stimulation and/or arousal, but can also occur by such causes as a full urinary bladder or spontaneously during the course of a day or at night, often during erotic or wet dreams. An erection results in swelling and enlargement of the penis or the swelling of the female counterpart to the penis, clitoris. Erections enable sexual intercourse and other sexual activities (sexual functions), though it is not essential for all sexual activities.