sexology

GONADS

The gonads are those specialized organs—the testes in the male and the ovaries in the female—that produce the sex cells (gametes) called sperm and ova (or eggs). The gonads also produce many hormones, which are usually called the sex hormones. This definition is misleading, however, because although these hormones are necessary for proper sexual functioning in the individual, they are also produced by other organs of the body and stimulate activities that are not sexual. Both "male" and "female" sex hormones are produced in each sex, although they appear in different concentrations.

The gonads are homologous organs that develop from undifferentiated gonadal tissue that appears during the developing embryo's fifth or sixth week of intrauterine life. Although the sex of the gonad is fixed at the time of fertilization by the presence of a single gene (the Testes Determining Factor) on the Y chromosome, determination of the gonad cannot be made until about the seventh week, when if it is not determined to be a testis, it is presumed to be an ovary. More precise definition occurs at about the tenth week, when the forerunners of the follicles become visible if the gonad is going to mature into an ovary.

The ovaries are nodular glands that, after puberty, have an uneven surface, are about one and a half inches long, weigh about 3 grams each, and are located one on either side of the uterus. They are held in place by folds and ligaments and are attached to the posterior surface of the uterus. The ovary contains thousands of microscopic ovarian follicles, which produce the ova. A female is born with all the immature ova she will ever produce (about 2 million, 40,000 of which survive to puberty; 400 mature during her reproductive lifetime, and only a few are ever fertilized). At puberty, the ova appear at differing stages of development.

The ovaries also secrete two important classes of hormones, the estrogens and the progestins. Estradiol is the most important of the estrogens and progesterone of the progestins, but in common usage, estrogen and progesterone represent the "female" sex hormones. These hormones control the production of secondary sex characteristics as well as other maturational changes that occur at puberty, but they do not seem to be crucial for differentiation of the female reproductive system before birth. They regulate the menstrual cycle and are necessary for reproduction. Their effect on female sex drive and behavior is unclear. They are essential for maintaining pregnancy. They are also important for menopausal women who may suffer from vaginal dryness and loss of calcium from the bones (osteoporosis). Many of these symptoms can be alleviated by the use of estrogen replacement therapy.

The word "testis" is the root word for "witness". in ancient times, a man would place his hand on his testes to swear that he was telling the truth—hence the word testify. They are two small ovoid glands about two inches long, weighing about 10 to 15 grams each, and suspended in a sac, the scrotum, beneath the penis. The left one usually hangs a bit lower than the right one. Attachments to the scrotum and the spermatic cords hold them in place. A fibrous capsule encases each testicle, extends into the gland, and divides it into about 200 conical lobes. Each lobe contains one to three tiny coiled seminiferous tubules, the combined length of all the tubules in both testes is about one-quarter mile. Interstitial cells (Leydig cells) are packed between the tubules. The tubules of each testis coalesce to form a tightly coded tube enclosed in a fibrous casing (the epididymis). The epididymis measures about 20 feet and lies along the top and side of the testis.

The male does not begin to produce sperm (spermatogenesis), a process that occurs in the seminiferous tubules, until he reaches puberty. Sertoli cells are interspersed among the developing sperm within the tubules and provide physical support and nutrition during their development. These cells also help to regulate the secretion of one of the sex hormones. Billions of sperm cells are produced and stored in the seminiferous tubules and eventually are moved into the epididymis by the contractions of the tubules. There they complete their maturation and become motile by the whiplash movement of their tail.

The androgens, of which testosterone is the most important, are the "male" sex hormones that are produced by the interstitial cells. The androgens are responsible for the embryonic development of the male reproductive system. They regulate the secondary sex characteristics that occur in the male at maturity and stimulate protein anabolism that promotes growth of skeletal muscles and bones. They are linked to the male sex drive, and possibly to male aggressive behavior.

The effects of the removal of the testes (castration) have been known for centuries. Eunuchs were created for sexual pleasure and for use as guards for the harem in many ancient cultures. During the 17th century, when women were not allowed to perform on the stage or sing in church, it was not uncommon to castrate young boys to retain their clear, high voices. They became very important in the choirs of the Roman Catholic Church and stars on the grand-opera scene.