Lesson of the day. 1 in a series of, well it'll last a week. 90+ words.
The pituitary gland, the prostate and testosterone all have an important role in the process of erection of a penis.
A penile erection 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 physiological 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 (see "nocturnal penile tumescence"). An erection results in swelling and enlargement of the penis. Erection enables sexual intercourse and other sexual activities (sexual functions), though it is not essential for all sexual activities.
In the presence of mechanical stimulation, erection is initiated by the parasympathetic division of the autonomic nervous system (ANS) with minimal input from the central nervous system. Parasympathetic branches extend from the sacral autonomic plexus into the arteries supplying the erectile tissue; upon stimulation, these nerve branches initiate the release of nitric oxide, a vasodilating agent, in the target arteries. The arteries dilate, filling the corpora spongiosum and cavernosa with blood. Erection subsides when parasympathetic stimulation is discontinued; baseline stimulation from the sympathetic division of the ANS causes constriction of the penile arteries, forcing blood out of the erectile tissue.
The cerebral cortex can initiate erection in the absence of direct mechanical stimulation (in response to visual, auditory, olfactory, imagined, or tactile stimuli) acting through erectile centers in the lumbar and sacral regions of the spinal cord. It is worth noting that the cortex can suppress erection even in the presence of mechanical stimulation (as can any number of other psychological, emotional, and environmental factors).
And now you know about Penile Erection.