Testosterone is an important male sex hormone produced in the testicles. It regulates sexual development, muscle density, and bone growth. It also ensures that the body makes enough red blood cells. When the brain receives signals that testosterone levels in the blood are low, it triggers a cascade of actions to produce more of the hormone.
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Testosterone production in men
Around 95% of testosterone is made in the testicles with the remaining 5% produced by the adrenal glands.
- When the hypothalamus in the brain detects that testosterone levels are low, it secrets the so-called gonadotropin-releasing hormone.
- At the back of the brain, the pituitary glands are set in action by the release of the gonadotropin-releasing hormone, and produce two other hormones: the follicle-stimulation hormone and the luteinizing hormone.
- Both of these hormones travel to the testicles where the follicle-stimulation hormone initiates sperm production and the luteinizing hormone triggers the Leydig cells to produce testosterone.
- Leydig cells then convert available cholesterol into testosterone.
- The testosterone is released into the bloodstream.
The body has its own feedback mechanisms. When testosterone levels get too low, it ramps up production of the hormone. When levels of the hormone are too high, the body blocks further production of testosterone.
Testosterone production in women
Women produce relatively small quantities of testosterone. But the hormone is nevertheless an important precursor for estrogen and helps to regulate muscle mass, mood, and libido.
In women, testosterone is produced predominantly in the ovaries and adrenal glands. Similar to men, the production of the hormone is set in motion by signalling via the luteinizing hormone.
Both men and women can have abnormally low or high levels of testosterone. In some cases, these conditions may require blood testing and treatment.
- Nassar GN, Leslie SW. Physiology, Testosterone. [Updated 2018 Oct 27]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK526128/
- Rommerts, F. (1990). Testosterone: an overview of biosynthesis, transport, metabolism and action. Testosterone, 1-22. https://doi.org/10.1007/978-3-662-00814-0_1
- Burger, H. (2002). Androgen production in women. Fertility and Sterility, 77: 3-5. https://doi.org/10.1016/s0015-0282(02)02985-0