The Male Reproductive System

A man's fertility and sexual characteristics are dependent on the normal functioning of the male reproductive system.

The testes

The testes are a pair of oval-shaped glands (15-35ml each in volume) that are suspended in the scrotum. The testes are the main male reproductive organ and are crucial for the normal functioning of the male reproductive system. The testes have two related but separate roles: Production of sperm, and production of the male sex hormone, testosterone. There are two separate compartments in the testes that reflect the two major functions. A testis contains a number of small, tightly packed, fine tubes called seminiferous tubules in which sperm are produced. These tubules, visible to the naked eye, are like a thick walled sausage with a fine hollow down the middle. The wall is made up of two types of cells. One being the Sertoli cells which 'nurse' the other cell type which are called germ cells or the precursors of sperm. The germ cells are squeezed between the larger Sertoli cells. Between the tubules lie another cell type, Leydig cells, which produce testosterone.

The location in the scrotum seems important by keeping the testis 2 to 3 degrees below normal body temperature. This is essential for fertility as a cooler temperature is necessary for good sperm production and proper testicular functioning.

The scrotum

The scrotum is a loose pouch of skin that hangs outside the body from the lower abdominal region behind the penis. The testes sit inside the scrotum.

The epididymis

The epididymis is a highly coiled tube (or duct) that lies at the back of the testes and connects the seminiferous tubules in the testis to another single tube called the vas deferens. The epididymis is approximately 5 metres long if outstretched. All sperm must pass through the epididymis when they leave the testis and undergo an important 'maturation' process that allows them to swim and fertilize the egg.

The vas deferens

The vas deferens is the tube that connects the epididymis to the urinary tract (urethra) at the back of the bladder, via the ejaculatory duct. The main function of the vas deferens and ejaculatory duct is to transport the mature sperm and seminal fluid to the urethra.

The ejaculatory duct

The ejaculatory duct is a tube that is formed by the joining of the vas deferens and the duct of the seminal vesicle. The ejaculatory duct empties into the urethra.

The urethra

The urethra (also called the prostatic urethra) is a tube that runs from the bladder to the end of the penis. It carries urine from the bladder to the outside of the body. In men, the urethra also carries semen out of the body. Since the bladder also empties into the urethra, the urinary and reproductive tracts come together. A ring of muscle called the internal sphincter is located at the base of the bladder and when closed, it stops urine and semen leaving the body through the urethra at the same time. At orgasm, this muscle ring closes tightly to stop sperm passing 'backwards' into the bladder.

The prostate gland

The prostate is a small yet important organ (or gland) found only in the male reproductive system. Its main function is to produce a fluid which protects and enriches sperm. Secretions from the prostate contribute to approximately 40% of the fluid volume of the ejaculate however the functions of the substances in the prostatic fluid are not entirely known.

In young men, the prostate is about the size of a walnut (20g) and it enlarges as a man gets older. It is located at the base of the bladder and is wrapped around the urethra, which carries urine from the bladder to the penis. The growth of the prostate is dependent on testosterone (male sex hormone). If the prostate grows too large, it may slow or stop the flow of urine. The location of the prostate near the rectum means that its growth can be checked by a rectal examination performed by a qualified medical practitioner.

The seminal vesicle

The seminal vesicles are two small glands that lie immediately above the prostate gland attached to the vas deferens near the base of the bladder. These glands are very active and produce a fluid that makes up about 50% of the fluid volume of the ejaculate. The fluid produced by the seminal vesicles is rich in fructose (a sugar) that may be important as an energy source for sperm. Several other proteins are also made which are involved in the rapid clotting of the ejaculate.

The penis

The penis is the male organ through which the urethra passes and is necessary for urination and sexual intercourse. When the urethra passes through the penis, it is referred to as the penile urethra. The penis becomes engorged with blood during sexual excitement or stimulation. This is an erection. During ejaculation, the ejaculate emits through the tip of the penis.