The main constituent of the testis, lined by Sertoli cells and containing the developing sperm cells. Lying between the tubules are the interstitial or Leydig cells.

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.

Cells of the testis lying between the testicular tubules in which sperm are formed (hence their other name, interstitial cells), and responsible for the production of the male sex hormone testosterone under the influence of luteinising hormone.

Tiny ducts (about 20 in number) connecting the testicular tubules with the epididymis.

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.

Cells in the testis lining the testicular tubules that nurture the developing sperm cells; responsible in fetal life for the production of anti-Mullerian hormone, which stops the male fetus from developing fallopian tubes, a uterus and a vagina. A source of estradiol in men.

The product of the spermatocyte in the testis when it has completed meiosis (by which the number of chromosomes is halved, so it's in the haploid state), and also enclosed in the testicular tubules by the Sertoli cells. Early spermatids are round-shaped, whereas late spermatids closely resemble mature spermatozoa.

The sperm cell equivalent to the oocyte stage of the egg. Further development in the testicular tubules results in a spermatid.

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.

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 stage of development of the maturing sperm cell, as it leaves the tubules of the testis the testicular tubules, to mature in the epididymis. Composed of a head (including the acrosome), a midpiece loaded with mitochondria to provide energy, and a tail, or flagellum, for propulsion. Packed into the head of the spermatozoon is a haploid number of chromosomes (there are normally 23, including either an X-chromosome or a Y-chromosome).

(TESE) Dissection into the testis itself, in men with azoospermia due to maturation arrest, to recover (by 'teasing out') immature sperm cells from the (often small) fraction of testicular tubules there which still contain such cells. The sperm cells are used for in vitro fertilisation using intracytoplasmic sperm insertion (ICSI).