Hormones, nerves, blood vessels and muscles work together to create penile erections. These occur throughout a male's life, even during childhood and adolescence. Nocturnal penile tumescence is the medical name for night-time erections among men. The National Health Institute reports that this occurrence typically happens three to five times throughout the night and is fairly common among males. Nocturnal penile tumescence is a condition that doctors continue to theorize and form opinions about as it is not yet fully understood.
Among the many possible reasons for night-time erection are sexual dreams. Consequently, in anticipation of sexual intercourse in the dream world, the penis becomes erect. A wet dream is a night erection that involuntarily creates semen ejaculation. According to the National Health Institute, this commonly occurs during the deep sleep phase of rapid eye movement, or REM.
Another reason for nighttime erection is that bladder control failure contributes to causing penile erection. It is thought that when the bladder swells to capacity during sleep, urine also fills the penis. Consequently, the urine makes the penis erect. During sleep, it is thought that men possess no control over their bodies. Physical and hormonal control is lost which ultimately fails to control erectile functions.
Blood vessels may enlarge when nitrous oxide is released, says the National Kidney and Urologic Diseases Clearinghouse This allows the blood flow to reach the penile tissue and create an erection. Nitrous oxide is naturally produced in different areas of the human body. It serves an important production role in the artery walls. This results in aiding sleep, relaxation and an enlarged penis.
Body tissues require oxygen to survive. Penile tissues receive large amounts of oxygen when the penis becomes erect. According to the University of Maryland, oxygen-rich blood is an important component for erectile health. During the night, the oxygenated tissues cause the penis to swell with blood.