Testosterone hormone (T) is an important sex hormone and anabolic steroid with important functions such as male reproduction, erection formation and development of secondary sex characteristics. Its deficiency (hypogonadism) causes many problems. In this article, I will give general information about the testosterone hormone and its functions.

What is the testosterone hormone?

Testosterone is an important male sex hormone produced predominantly from the testicles in men. It is responsible for the development of male reproductive organs and male secondary sex characteristics in males. In women, very little is made from the ovaries and converted into other female sex hormones. Pregnant women have higher testosterone levels than non-pregnant women.

Where is testosterone made in the body?

This hormone is mostly made by the testicles in men. It is the main hormone that develops masculine characters in men. It is found in very small amounts in women. In women, a small amount is secreted from the ovaries. In both sexes, male hormone is released from the adrenal glands. Dehydroepiandrosterone (DHEA) hormone made in the adrenal gland turns into testosterone and estrogen hormones in the body. In the prostate gland, the testosterone hormone is converted to dihydro testosterone (DHT) by the enzyme 5-alpha reductase.

The precursor for testosterone production is cholesterol, that is, it is made from cholesterol. However, this does not mean that as the amount of cholesterol increases, testosterone production will also increase. T production is kept under control at certain levels by the hypothalamus and pituitary glands.

How is testosterone production regulated?

The level of male hormone in the body is kept in a certain balance. Hormone levels are higher in the morning hours. The production of the hormone is controlled by two important glands in the central nervous system, called the hypothalamus and the pituitary. Gonadotropin-releasing hormone (GnRH) secreted from the hypothalamus stimulates the pituitary to release luteinizing hormone (LH). The LH hormone also mixes with the blood and stimulates the testis and provides testosterone synthesis. LH hormone stimulates the production of estrogen and progesterone mainly by stimulating the ovaries in women.

As the T hormone produced from the testicles increases in the blood, it affects the hypothalamus and suppresses the secretion of GnRH. In this way, the T hormone in the blood is kept in a certain balance.

In any disease that occurs in the hypothalamus, pituitary and testicles, disruptions in the production of T hormone and abnormalities in blood levels occur. Thyroid hormones and prolactin hormone are also hormones that have effects on T production.

How does testosterone production change with aging?

Testosterone production is at its highest during adolescence and early adulthood. It has the highest value at the age of 20-25 in adults and the lowest at the age of 65-70 years. With aging, T production begins to decrease gradually. After an average of 30-40 years, a decrease of 1% is observed in men. It is necessary to distinguish this decrease, which occurs with aging, from hypogonadism. While the decline in old age is normal, hypogonadism is a disease and there is severe T hormone depletion and treatment is required. In hypogonadism, there is a problem at the level of the testis, hypothalamus, or pituitary.

How is testosterone level measured?

If it is thought that there is an irregularity in the level of testosterone hormone, measurements are made by taking blood. For measurement, blood is taken from the arm vein. Since T hormone production is highest in the morning hours, the ideal is to have blood taken between 7-10 am. Blood T measurement is usually not done alone, but together with FSH and LH measurements. Because T production takes place under the control of these hormones. Briefly, the following three tests are checked in the blood taken for T measurement:

• Total testosterone: Since the production of this hormone is highest in the morning hours, it is important to bleed during these hours.
• FSH begins to test.
• LH test

What does total and free testosterone mean?

The T hormone is present in the blood in two forms: Total testosterone (TT) and free testosterone (free testosterone, Ft).

• Total testosterone: Most of the testosterone in the blood is bound to proteins. These proteins are albumin and sex hormone binding globulins (SHBG).
• Free testosterone: The part of the hormone that is not bound to proteins is known as the free hormone.

In practice, T hormone measurements generally measure the total hormone level. Testosterone that is free and bound to albumin is known as “bioavailable” testosterone (the active, functional part). It is this form of the hormone that can be easily used by the body and is functional. If the total value is low, then the free amount may also be low and therefore the bioavailable level is low.

What are the normal values ​​for testosterone?

It is important that the T hormone is at normal values. Normal values ​​vary with age, lifestyle, dietary habits and general health. Serious problems arise, especially in low (hypogonadism). Normal values ​​should be in the following ranges:

• Adult males: 280-1100 ng/l or (10-35 nm/L)
• Adult women: 15-70 ng/dl or (0.5-2.4 nmol/L)

What are the functions of the testosterone hormone, what does it do?

The T hormone has very important functions in the human body. These tasks can be grouped into two main groups. These are anabolic and androgenic effects. The anabolic effect is associated with muscle and bone development and strengthening. Androgenic effect is related to the development of sex organs and secondary sex characteristics. These tasks arise in different ways at different stages of life. We can examine them in 3 periods:

• During the development of the fetus (during the development of the child in the mother’s womb)
• During adolescence in boys
• In adult males

T tasks during the development of the fetus

The T hormone plays an important role in child development during pregnancy. When pregnancy occurs, it initiates the development of the testicles in fetuses with the male sex associated with the sex on the Y chromosome at 7 weeks of age. The T hormone produced from the testicles also ensures the development of male internal and external reproductive organs throughout development in the uterus.

Duties of T in adolescence in boys

T has important functions during puberty in boys born as boys. We can summarize them as follows:

• •Height growth
• Increased hair growth in different parts of the body and genital areas
• Penis development and growth
• Enlargement of testicles, prostate and other reproductive organs, increased libido (sexual desire, increased sexual desire)
• Male voice development (male voice)
• Duties of T in adult males
• Testosterone has very important functions in adult men. In the absence of T hormone, many functions are impaired in men. We can list these tasks as follows:
• Sperm production
• Erythrocyte production (sends necessary warnings for the production of red blood cells)
• Muscle development and strengthening
• Increase in facial hair (beard and mustache development)
• Bone development and strengthening
• Increased libido (increased sexual desire)
• Well-being
• Mental functions
• Hair loss (male baldness in the forehead area)
• Regulates body fat distribution
• Regulation of erectile functions (related to erection)

T’s functions in adult females

The main task of T in people born and developed as women is on libido. This hormone has a libido-increasing effect in adult women. Most of this hormone produced by the ovaries in women is converted to estradiol. Estradiol is a hormone of primary importance in women. Other hormones that are essential for women are estrogen and progesterone.

In summary: Testosterone is a male sex hormone with anabolic and androgenic effects. It is important for the development of male secondary sex characteristics, reproductive and sexual functions, and the development of reproductive organs. In its deficiency, reproductive system and sexual functions are impaired. Regressions are observed in other secondary sex characters.

Prof. Dr. Emin ÖZBEK

Urology Specialist

Istanbul- TURKEY