The Human Body

Male Sexual Organs

The external sex organs of men are the penis and the scrotum. The penis is a sensitive organ important to reproduction and urination and to sexual pleasure. At its tip is the glans, which contains the urethral opening, through which urine passes. The ridge that separates the glans from the body of the penis is called the corona (Latin for “crown”), or coronal ridge. The glans and the corona are the most sensitive parts of the penis. The glans is covered with a foreskin (prepuce) unless the man has been circumcised, in which case the foreskin has been surgically removed.

The penis contains three cylinders of tissue that run parallel to the urethra. During sexual arousal, these tissues become engorged with blood and expand, causing the penis to enlarge and become erect (erection or tumescence). Men do not have a penis bone or a muscle that causes erection, as do some other animals.

The scrotum is a pouch that hangs below the penis and contains the two testes, which produce sperm (the male sex cell responsible for fertilization) and are considered part of the internal genitalia. The testes also are the primary producers of testosterone (male sex hormone) in men. Inside the testes are about 1000 seminiferous tubules that manufacture and store the sperm. The scrotum can pull up closer to the body when the surrounding temperature is low and can drop farther away when the temperature is hot in order to keep the testes at an optimal, constant temperature somewhat lower than body temperature.

After sperm are produced, they move out of the testes and into the epididymes, a long tube coiled against the testes, where the sperm are stored and mature. The vas deferens transports the sperm from the epididymes through the prostate, after which the vas deferens becomes the ejaculatory duct. Here, fluids from the prostate and seminal vesicles (small sacs that hold semen) combine with the sperm to form semen, a thick, yellowish-white fluid. The average discharge of semen, called ejaculate, contains approximately 300 million sperm.