Anatomy and physiology of the penis
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:
- glans – The head of the penis is called the glans (glans penis). It contains the opening of the urethra (urethral meatus). The skin of the glans is very thin and contains nerves for sexual stimulation. The glans is covered by a loose fold of moveable skin called the foreskin (prepuce). Sometimes the foreskin is surgically removed in an operation called a circumcision.
- shaft – The main body of the penis is called the shaft. It is made up of soft, spongy erectile tissue that contains many blood vessels. The erectile tissue is wrapped in connective tissue and covered with skin. The shaft has 3 chambers:
- The corpora cavernosa (singular: corpus cavernosum) are the 2 upper chambers of the shaft that make up most of the penis.
- The corpus spongiosum is the lower chamber of the shaft that surrounds the urethra.
- root – The base of the penis that is contained within the pelvis is called the root.
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. Semen 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.
The 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).