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What is testosterone?

Updated Tuesday, 19th March 2019

Find out more about the so-called sex hormone testosterone.

What makes a man male? Testosterone!

Testosterone is the male sex hormone. In males, testosterone production begins before birth, influencing the development of the male genitals, the brain, kidneys, muscles and liver.


Mini lecture

What is testosterone?

Claire Rostron:

Testosterone is a chemical substance known as a hormone and it can have quite wideranging effects through the body and that’s because it’s released into the bloodstream and therefore it can go around the body in the blood circulation and affect a wide range of organs. Testosterone is made in males in Leydig cells in the testes. There’s also a small amount made in the ovaries in females, and in both sexes is made in the adrenal glands which sit on top of the kidneys.

Now, the release of testosterone is controlled by a group of structures called the hypothalamic-pituitary-adrenal axis, and these include the hypothalamus in the brain, the pituitary gland at the base of the brain, and the adrenal glands on top of the kidneys. The release of testosterone generally occurs in two quite big surges in the body and these happen at around seven weeks of fetal development, and that’s associated with the development of the male genitalia, and it happens again at around age twelve and that’s associated with puberty. So as well as those physical characteristics, the release of testosterone is also associated with larger body bills, increased muscle mass and more and more bodily hair. But it’s also associated with some interesting psychological characteristics as well, and these include, greater aggression, more dominant behaviour, but also really interesting behaviour known as risk-taking.

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In childhood, testosterone levels are low, with production increasing rapidly at puberty. Secreted from the cells of Leydig in the testes, it controls the development of secondary sexual characteristics.

In teenage boys testosterone creates a deeper voice, a larger skeleton, body hair, developing reproductive organs and "male" patterns of behaviour.

Testosterone increases muscle bulk as it encourages protein formation and induces the retention of nitrogen. Testosterone controls sperm production, sexual drive and sexual performance throughout a man’s life.

But to define it purely in terms of sex would be misleading - it’s also a major regulator of sugar, fat and proteins in the human metabolism.

Women also produce testosterone, in lower levels, and as well as affecting their sex drive, it helps with energy levels and general sense of well-being.

Testosterone [Image: Linden Tea under CC-BY-NC-ND licence] Creative commons image Icon LindenTea via Flickr under Creative-Commons license Testosterone in a bottle.
The testosterone molecule’s structure is C19H28O2. It’s a member of the steroid compounds, of which the cholesterol molecule is also a member.

In fact, the testosterone molecule is a shortened version of the cholesterol molecule (without the hydrocarbon tail of cholesterol).






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