The male reproductive system governs sexual reproduction in men. The system is controlled by hormones and by physical stimuli acting on the sensitive nerve endings in the genital region. This system includes the penis, the prostate gland and a pair of testes encased in the scrotum.
The scrotum hangs outside the body below the base of the penis. This placement allows the temperature of the testes to be controlled by contraction or relaxation of the muscles in the scrotum. In order to produce sperm, the testes must be slightly cooler than the normal body temperature of 98.6 degrees Fahrenheit, or 37 degrees Celsius. Each testis hangs in its own compartment within the scrotum. Testes are responsible for creating testosterone, the male sex hormone.
Sperm is produced in the seminiferous tubules inside the testes. A young adult male can produce as many as 120 million sperm each day. The sperm are stored in the vas deferens, which is located just behind the pubic bone. Sperm can remain in the vas deferens for about a month and still remain viable.
The prostate is located close to the bladder and wraps partway around the urethra. Glands in the prostate produce a liquid that helps transport sperm. Another fluid, which contains an energy source for the sperm, is created in the seminal vesicles. Sperm mixes with these fluids to form seminal fluid.
During ejaculation, the seminal vesicles contract. This causes the seminal fluid to move into the urethra, a tube located inside the penis. Seminal fluid exits the body through the urethra. The urethra is responsible for transporting both urine and sperm, though it cannot transport both at the same time.
When nerves in the penis are stimulated, they send messages asking for more blood to be pumped to the genital region of the body. Arteries in the penis fill with blood, causing the penis to become erect. Blood cannot drain out of the region because the veins are closed by pressure from the surrounding tissues. Once ejaculation occurs, the pressure relaxes and the veins are able to circulate blood normally.