Testosterone is a vital hormone that is responsible for the development of male physical characteristics. In men, testosterone is primarily produced in the testes, but several parts of the body have to work together to ensure that testosterone is produced correctly and the body remains healthy.
In this guide, we’re going to look at how testosterone is produced in men, starting with the brain but then moving onto the testes as well the other parts of the body.
The hypothalamus is the part of the brain responsible for homeostasis, or the internal balance of the body. This includes the production of hormones for the endocrine system, as well as linking the endocrine system to the nervous system. It is the hypothalamus that initially triggers the release or inhibition of hormones. In the case of testosterone, it is the hypothalamus that tells the pituitary gland it must release hormones to stimulate testosterone production. To do this, the hypothalamus releases gonadotrophin-releasing hormone.
The two different hormones released by the pituitary gland serve different purposes on reaching the testes. FSH is responsible for sperm production, whilst LH specifically stimulates the production of testosterone. It does this by influencing a special type of cell called a Leydig cell. When Leydig cells are activated, they begin to convert cholesterol into testosterone.
Most cholesterol reaches the bloodstream through diet, particularly in foodstuffs such as bacon and eggs. Cholesterol can be produced by the testes if there is not enough in the bloodstream, but this is less effective and can inhibit the Leydig cells. It is cholesterol absorbed from the bloodstream that is most important for testosterone production.
There is a small amount of testosterone produced by the adrenal glands, only about 5%. The other 95% in men comes from the testes. In women, the majority of their (lower level of) testosterone comes from the ovaries, though again some is produced in the adrenal glands.
Many of the hormones that control the endocrine system have their origins in the pituitary gland (a pea-sized gland found at the base of the brain). As well as the testes, the adrenal glands and thyroid gland are at least partially controlled by the pituitary gland. The hypothalamus gives the instruction, but then the pituitary gland actually releases or inhibits the hormones.
When the hypothalamus tells the pituitary gland that the testes need to produce more testosterone, the pituitary gland begins releasing other hormones, known as gonadotrophic substances. These include follicle-stimulating hormone (FSH) and luteinising hormone (LH). LH, in particular, will compel the testes to produce more testosterone. If the level of testosterone rises by too much, the hypothalamus will tell the pituitary gland to stop producing LH.
Newly produced testosterone is sent from the testes to the bloodstream to be carried where it is needed. Some will become inert when it attaches to various proteins, whilst a small amount will freely travel to areas of the body where masculine characteristics develop. If the hypothalamus decides that testosterone in the blood has achieved an appropriate level, it will reduce its production of gonadotrophin-releasing hormone, which in turn will cause the pituitary gland to reduce its production of LH. This production and reduction forms an ongoing cycle.
Sometimes, the body will not produce the correct amount of testosterone. Excess testosterone can cause early puberty in younger children, sometimes leading to infertility. Conditions that cause excess testosterone production include congenital adrenal hyperplasia, androgen resistance and ovarian cancer. Use of anabolic steroids can also interfere with testosterone levels.
Low testosterone can delay puberty, as well as having a negative effect on muscle mass, bone density, body fat, libido and mood. It is known as hypogonadism. Some reduction in testosterone production is normal as a man ages.