The penis is part of the male reproductive system and urinary system. The main structures of the male reproductive system are the testicles, epididymis, seminal vesicles, prostate and penis. The internal parts of the male reproductive system are located in the lower pelvic cavity between the hip bones. The penis hangs in front of the pouch of skin (scrotum) that contains the testicles.
The penis is rod-shaped and is divided into 3 parts:
Inside the penis is a thin tube called the urethra. The urethra extends from the base of the bladder to the tip of the penis.
The penis is part of the urinary system. It contains the urethra, which carries urine from the bladder to the outside of the body.
The penis is also a male sex organ. During an erection, nerves signal the blood vessels inside the erectile tissue of the penis to fill with blood. When the blood flow increases, the spongy tissue expands and causes the penis to stiffen and enlarge. This allows the penis to be inserted into the vagina during sexual intercourse. SemenSemenThe fluid released from the penis during orgasm that contains sperm from the testicles and fluid from the prostate and seminal vesicles (a pair of pouch-like structures close to the prostate). passes into the urethra and out the tip of the penis when a man ejaculates. Semen is the fluid that contains sperm. After a man ejaculates, the blood flows back into the body and the penis becomes soft again.