Testosterone

Testosterone is a steroid hormone involved in reproductive development, sexual function, muscle and bone maintenance, and other processes in people of all sexes. It is produced mainly by the testes and, in smaller amounts, by the ovaries and adrenal glands.

Hypothalamic–pituitary–gonadal axis: A hormonal signaling system linking the hypothalamus, pituitary gland, and gonads to regulate reproductive function. It controls testicular testosterone production through feedback among the brain, pituitary, and gonads.
Androgen: A class of hormones that promotes or maintains male-typical reproductive development and other physiological traits. Testosterone is the principal circulating androgen in many human contexts.
Testosterone replacement therapy: Medical treatment that supplies testosterone to people with confirmed deficiency or for other specified indications. It aims to restore hormone levels or produce desired physiological effects under clinical monitoring.
Spermatogenesis: The process by which sperm cells develop from germ cells in the testes. Testosterone within the testes is necessary for normal sperm production.
Testosterone deficiency in aging men: A clinical question concerning low testosterone in older men and its relation to symptoms and health outcomes. Age-related level changes do not alone establish whether treatment is beneficial.
Luteinizing hormone: A pituitary hormone that stimulates gonadal hormone production and ovulation. In the testes, it stimulates Leydig cells to produce testosterone.
Steroid hormone: A hormone derived from cholesterol that can cross cell membranes and bind intracellular receptors. Testosterone’s steroid structure shapes how it travels and signals in the body.
Hypogonadism: A condition in which the gonads produce insufficient sex hormones, sometimes with impaired reproductive function. Low testosterone can result from disorders affecting the testes or their hormonal control.
Erythropoiesis: The production of red blood cells, primarily in bone marrow. Testosterone can stimulate red-cell production, which helps explain treatment-related rises in hematocrit.
Testosterone and cardiovascular disease: Research on associations between testosterone levels or treatment and cardiovascular outcomes. Evidence about cardiovascular effects of testosterone therapy has required careful study and interpretation.

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