The testicles, or testes – the terms are synonymous, are the male sex glands and correspond to the ovaries in the female. Like small chicken eggs in size and shape, they develop up near the kidneys while the child is still in the womb. Just before birth they descend through openings in the lower part of the front of the abdomen to their permanent position suspended between the thighs behind the penis in a pouch of skin called the scrotum. Like the ovaries, the testicles have two functions – to produce male sex cells, or sperm, and to manufacture male hormones.
The reason why the testicles are located outside the body is that sperm production requires a slightly lower temperature (by about 3-5 degrees) than that maintained by the rest of the body. The correct temperature is so important that if it is varied even slightly (eg. by the wearing of tight pants), the production of sperm may temporarily cease. The scrotum provides its own temperature control, contracting to keep the testicles warm in cold weather and relaxing when the temperature rises.
Each testicle is made up of millions of tiny, coiled tubes in which sperm (spermatozoa) are continuously manufactured. Inside each testicle are 150 metres of tiny coiled up tubes. Over a period of 70 days stem cells in the testicle multiply thousands of times as they move down the tube to generate millions of sperm. About 300 million sperm are produced every day. Once manufactured, the sperm mature in a network of tubes called the epididymis, situated at the back of the testicle. After about 2-4 weeks when they acquire the ability to propel themselves, they are transferred through a duct called the vas deferens, extending upwards into the body from the epididymis, looping beside the bladder until they reach the seminal vesicles, which are two small pouches just behind the prostate gland. Here the sperm are stored until they are either ejaculated or eventually die and are reabsorbed into the body.
The testicles also produce the male hormone, testosterone, which at puberty gives rise to the development of the recognisable male characteristics, such as a deep voice, the growth of facial and bodily hair, and the development of the male genitals.
Unlike women, men’s ability to reproduce does not come to a definite end in mid-life. The production of sperm and testosterone starts to decrease as early as 20 years of age, but it merely continues to decline rather than ceasing completely. Even men in their seventies can produce sperm, and a few (about 10%) can continue into their eighties.
Occasionally one or both testicles fail to descend fully as they should in a young child, in which case they will not function properly.
It is normal for the testicles to hang unevenly. In most men the left testicle hangs lower than the right, but in some dominantly left handed men the reverse arrangement applies.