Development of a sperm cell, in the tubules of the testes (the testicular tubules), from spermatogonium and spermatocyte to spermatozoon (the last part of this process, from spermatid to spermatozoon, is called spermiogenesis). The process of spermatogenesis takes 56 days. At any one location in a tubule there are cells at four different stages of maturity, so mature sperm are released from a particular location into the lumen of the testicular tubules every 14 days. A systematic interruption of spermatogenesis results in azoospermia and is called maturation arrest.

A complete absence of sperm (spermatozoa) in the semen. Detectable only by performing a sperm count, as semen looks the same whether it contains sperm or not. Due either to an obstruction (usually in the epididymis or vas deferens), and called obstructive azoospermia, or to failure of sperm to form or to mature in the testis (called maturation arrest). See also spermatogenesis and testicular sperm extraction (TESE).

(FSH) The hormone, or gonadotropin, produced by the pituitary gland that in women stimulates the tertiary follicle to grow; in men it stimulates spermatogenesis. Obtained from human sources in a mixture with luteinising hormone (LH) as (1) human menopausal gonadotropin (hMG), extracted from the urine of women who have been through the menopause (Humegon, Metrodin and Pergonal); and (2) human pituitary gonadotropin (hPG), from human pituitary glands removed at autopsies (now obsolete). Today, pure FSH is made synthetically with gene technology (recombinant FSH), such as Gonal-F and Puregon.

Any hormone that switches on the function of the gonads. There are two main families of gonadotropins: (a) the gonadotropin that stimulates the growth of the follicle, or follicle stimulating hormone (FSH); and (b) those that cause ovulation from the mature follicle and stimulate the corpus luteum that results to develop and to produce progesterone, namely luteinising hormone (LH) and human chorionic gonadotropin (hCG). FSH will cause growing follicles to produce the estrogen estradiol, provided that a small amount of LH (or hCG) is present. FSH and LH are produced in the pituitary gland, whereas hCG comes from the placenta in pregnancy. In men, FSH stimulates the Sertoli cells of the testicular tubules, and hence drives spermatogenesis; LH and hCG stimulate the Leydig cells to produce testosterone.

A protein hormone produced in women by developing follicles as well as by the corpus luteum, and in men by the testis in the presence of spermatogenesis, and acting on the pituitary gland to inhibit the production of follicle stimulating hormone. In women, falling levels occur as the number of developing follicles reduces to low numbers leading up to menopause, thus causing the elevation of serum FSH and shortening of the follicular phase that characterises the premenopause. In men, appreciable levels of serum inhibin B, a subclass of the inhibin family, predicts the presence of at least a small amount of sperm production.

The form of the sperm cell (or male gamete) at the first stage of spermatogenesis, by which spermatogonia enter meiosis to start to reduce the number of chromosomes for the more mature sperm cells (the spermatozoa) that will eventuate.

The form of the sperm cell in the second stage of spermatogenesis (through which the sperm cells are formed in the testes), produced from primary spermatocytes in the first cell division of meiosis, and giving rise to spermatids, which have just half the normal cell's complement of chromosomes, through the second division of meiosis; enveloped by Sertoli cells in the testicular tubules.

The replicating phase of the sperm cell in the testis, equivalent to the oogonium in the ovaries, but, unlike the oogonia, spermatogonia normally persist until old age. Located among the supporting cells (Sertoli cells) in the testicular tubules. Divides by the process of mitosis until it begins to undergo meiosis by changing into the primary spermatocyte, the first step in the process of sperm cell formation, or spermatogenesis. Plural: spermatogonia.

The final part of the formation of a mature sperm cell, in which the round, early spermatid (already with a haploid number of chromosomes) loses its round shape to acquire the features of the mature, elongated spermatozoon. Contrast with spermatogenesis, which encompasses spermiogenesis as it's completed.