Male Reproductive System

The organs of the male reproductive system are specialized for the following functions:

• To produce, maintain and transport sperm (the male reproductive cells) and protective fluid (semen)
• To discharge sperm within the female reproductive tract
• To produce and secrete male sex hormones

The male reproductive anatomy includes internal and external structures.

What are the external reproductive structures?

Most of the male reproductive system is located outside of the man’s body. The external structures of the male reproductive system are the penis, the scrotum and the testicles.

Penis — The penis is the male organ for sexual intercourse. It has three parts: the root, which attaches to the wall of the abdomen; the body, or shaft; and the glans, which is the cone-shaped end of the penis. The glans, which also is called the head of the penis, is covered with a loose layer of skin called foreskin. (This skin is sometimes removed in a procedure called circumcision.) The opening of the urethra, the tube that transports semen and urine, is at the tip of the glans penis. The penis also contains a number of sensitive nerve endings.

The body of the penis is cylindrical in shape and consists of three internal chambers. These chambers are made up of special, sponge-like erectile tissue. This tissue contains thousands of large spaces that fill with blood when the man is sexually aroused. As the penis fills with blood, it becomes rigid and erect, which allows for penetration during sexual intercourse. The skin of the penis is loose and elastic to accommodate changes in penis size during an erection.

Semen, which contains sperm, is expelled (ejaculated) through the end of the penis when the man reaches sexual climax (orgasm). When the penis is erect, the flow of urine is blocked from the urethra, allowing only semen to be ejaculated at orgasm.

Scrotum — The scrotum is the loose pouch-like sac of skin that hangs behind the penis. It contains the testicles (also called testes), as well as many nerves and blood vessels. The scrotum has a protective function and acts as a climate control system for the testes. For normal sperm development, the testes must be at a temperature slightly cooler than the body temperature. Special muscles in the wall of the scrotum allow it to contract and relax, moving the testicles closer to the body for warmth and protection or farther away from the body to cool the temperature.

Testicles (testes) — The testes are oval organs about the size of large olives that lie in the scrotum, secured at either end by a structure called the spermatic cord. Most men have two testes. The testes are responsible for making testosterone, the primary male sex hormone, and for generating sperm. Within the testes are coiled masses of tubes called seminiferous tubules. These tubules are responsible for producing the sperm cells through a process called spermatogenesis.

Epididymis — The epididymis is a long, coiled tube that rests on the backside of each testicle. It functions in the transport and storage of the sperm cells that are produced in the testes. It also is the job of the epididymis to bring the sperm to maturity, since the sperm that emerge from the testes are immature and incapable of fertilization. During sexual arousal, contractions force the sperm into the vas deferens.

What are the internal reproductive organs?

The internal organs of the male reproductive system, also called accessory organs, include the following:

• Vas deferens — The vas deferens is a long, muscular tube that travels from the epididymis into the pelvic cavity, to just behind the bladder. The vas deferens transports mature sperm to the urethra in preparation for ejaculation.
• Ejaculatory ducts — These are formed by the fusion of the vas deferens and the seminal vesicles. The ejaculatory ducts empty into the urethra.
• Urethra — The urethra is the tube that carries urine from the bladder to outside of the body. In males, it has the additional function of expelling (ejaculating) semen when the man reaches orgasm. When the penis is erect during sex, the flow of urine is blocked from the urethra, allowing only semen to be ejaculated at orgasm.
• Seminal vesicles — The seminal vesicles are sac-like pouches that attach to the vas deferens near the base of the bladder. The seminal vesicles produce a sugar-rich fluid (fructose) that provides sperm with a source of energy and helps with the sperms’ motility (ability to move). The fluid of the seminal vesicles makes up most of the volume of a man’s ejaculatory fluid, or ejaculate.
• Prostate gland — The prostate gland is a walnut-sized structure that is located below the urinary bladder in front of the rectum. The prostate gland contributes additional fluid to the ejaculate. Prostate fluids also help to nourish the sperm. The urethra, which carries the ejaculate to be expelled during orgasm, runs through the center of the prostate gland.
• Bulbourethral glands — The bulbourethral glands, or Cowper’s glands, are pea-sized structures located on the sides of the urethra just below the prostate gland. These glands produce a clear, slippery fluid that empties directly into the urethra. This fluid serves to lubricate the urethra and to neutralize any acidity that may be present due to residual drops of urine in the urethra.

How does the male reproductive system function?
The entire male reproductive system is dependent on hormones, which are chemicals that stimulate or regulate the activity of cells or organs. The primary hormones involved in the functioning of the male reproductive system are follicle-stimulating hormone (FSH), luteinizing hormone (LH) and testosterone.

FSH and LH are produced by the pituitary gland located at the base of the brain. FSH is necessary for sperm production (spermatogenesis), and LH stimulates the production of testosterone, which is necessary to continue the process of spermatogenesis. Testosterone also is important in the development of male characteristics, including muscle mass and strength, fat distribution, bone mass and sex drive.

Does a man go through menopause?

Menopause is a term used to describe the end of a woman's normal menstrual function. Female menopause is characterized by changes in hormone production. The testes, unlike the ovaries, do not lose the ability to make hormones. If a man is healthy, he may be able to make sperm well into his 80s or longer.

On the other hand, subtle changes in the function of the testes may occur as early as 45 to 50 years of age, and more dramatically after the age of 70. For many men, hormone production may remain normal into old age, while others may have declining hormone production earlier on, sometimes as a result of an illness, such as diabetes.

Whether waning testicular function contributes to such symptoms as fatigue, weakness, depression or impotence often remains uncertain.

Can "male menopause" be treated?

If testosterone levels are low, hormone replacement therapy may help relieve symptoms, such as the loss of interest in sex, depression and fatigue. However, replacing male hormones can worsen prostate cancer and, perhaps, atherosclerosis (hardening of the arteries).