Hormonal Disorders in Men – Primary Male Hormones

Hormones play a vital role not only in our metabolism, they are also vital for fertility, and aging. However, whenever there’s a mention of testosterone, there’s always the association of a risk-taking behavior, aggression, libido, and bad decision making.

Far from that, male hormones are essential for proper functioning of the body and there’s more to them than just testosterone. A whole gamut of androgens, and other hormones are responsible for muscle growth, hair growth, the transition to puberty, and fertility. Any disruptions in these hormonal levels lead to conditions like decreased libido, and sexual dysfunction.

What are these male hormones and how do they work?

Hormones controlling the male reproductive system, and secondary sexual characteristics work in a complex sequence. This is called a feedback circuit that works between the hypothalamus, pituitary glands, and the testes in tandem with the nervous system. It is a system called the hypothalamic-pituitary-gonad axis.

There are some hormones that trigger the release of other hormones. These are called the tropic hormones. Tropic hormones stimulate the release of other hormones and the other hormones act on different organs of the body creating responses like production of sperms and change in emotions.

Sequential production of male hormones:

Hormone Area of Production Target Organ
Gonadotropin-Releasing Hormone Hypothalamus Anterior Pituitary Gland
Follicle-Stimulating Hormone Anterior Pituitary Hormone Testes for production of sperm (spermatogenesis)
Luteinizing Hormone Anterior Pituitary Hormone Interstitial cells of testes for production of testosterone
Testosterone Testes Entire circulatory system
Inhibin Testes Testes to regulate maturation and health of sperms

How are male hormones produced?

Gonadotropin-releasing hormone

This is released in the hypothalamus of the brain. Hypothalamus is located just above the pituitary gland and is connected to it. Since the hypothalamus produces hormones that control the gonads, the hormone is called gonadotropin-releasing hormone (GnRH). Gonadotropin-releasing hormone is produced by specialized nerve cells in the hypothalamus.

Functions of gonadotropin-releasing hormone include stimulation of production of follicle-stimulating hormone and luteinizing hormone. Though gonadotropin-releasing hormone levels are low in childhood, with the approach of puberty, the levels increase leading to sexual maturation.

However, the levels of gonadotropin-releasing hormone, follicle-stimulating hormone, and luteinizing hormone are regulated by the levels of testosterone. This is an amazing balance mechanism in order to avoid excess or low levels of GnRH.

Gonadotropin-releasing hormone levels increase in cases of pituitary tumors. Levels reduce in children with genetic disorders like Kallmann’s syndrome. This condition leads to no pubertal development. In adult men who have already reached sexual maturity, trauma/damage can lead to low levels of gonadotropin-releasing hormone. This leads to a loss of sperm production and thus infertility.

Follicle-stimulating hormone

This is stimulated by GnRH and is produced in the anterior pituitary gland. It is produced along with luteinizing hormone. Follicle-stimulating hormone is vital for sexual maturation in both men and women. In men, follicle-stimulating hormone acts on specific cells of the testes (Sertoli cells). This action stimulates the production of sperms and is called spermatogenesis.

Though GnRH stimulates the release of follicle-stimulating hormone, other hormones present in the testes (testosterone and inhibin) regulate the levels of follicle-stimulating hormone and vice versa.

Once the anterior pituitary gland releases the follicle-stimulating hormone, it travels through the bloodstream and enters the testes. Here, the follicle-stimulating hormone stimulates the production of testosterone. However, when the levels of testosterone increases, nerves sense this and send messages to reduce the levels of GnRH so that levels of follicle-stimulating hormone is reduced. When testosterone levels decrease, there is a negative feedback effect and the levels of GnRH increases.

Follicle-stimulating hormone levels increase or decrease due to certain malfunctions or disease conditions of the testes. Levels rise when the testes cannot make enough testosterone. This leads to feedback control (communication) loss and high levels of follicle-stimulating hormone. This condition is called as hypergonadotropic-hypogonadism. This condition is caused due to testicular failure and is commonly seen in Klinefelter’s syndrome.

Reduced levels of follicle-stimulating hormone can lead to no/delayed puberty, and infertility.

Luteinizing hormone

This hormone like follicle-stimulating hormone is stimulated by GnRH and is produced in the anterior pituitary glands. It travels in the bloodstream and reaches the testes. Here, it stimulates the Leydig cells in order to produce testosterone and assists in sperm production.

As in the follicle-stimulating hormone, a feedback mechanism exists for the levels of luteinizing hormone. When hormones produced in the testes decrease, the levels of GnRH increase stimulating the production of luteinizing hormone. On the other hand, when hormones produced in the testes increase, the levels of GnRH decrease so that the level of luteinizing hormone reduces. This is a negative feedback. This inter-regulation of luteinizing hormone is important for fertility.

Higher levels of luteinizing hormone is an indicator of infertility. Lower levels of luteinizing hormone also leads to infertility as it cannot support the production of testosterone.

Testosterone

This is produced by the action of both follicle-stimulating hormone and luteinizing hormone. Testosterone is responsible for the development of reproductive organs and sperm production in men. Though testosterone has many other functions apart from sexual development, it is a vital hormone for enhancement of libido, and fertility. Testosterone is responsible for changes that occur during puberty in boys.

In order to facilitate the feedback mechanism where the levels of follicle-stimulating hormone and luteinizing hormone are regulated, testosterone is converted into an androgen dihydrotestosterone. Testosterone levels are regulated by the hypothalamus and pituitary gland. When the levels of testosterone increase/decrease, the feedback mechanism gets triggered and levels are balanced.

Testosterone levels increase more often in women than in men. In men, along with age, there is a gradual decline in the levels of testosterone. Testosterone deficiency can occur in the womb wherein male children do not develop male characteristics. Some children might have lower levels of testosterone during puberty leading to slower development of sexual characteristics. Adult men are also susceptible to lower testosterone levels leading to infertility, low libido, and other complications.

Inhibin

This hormone is released in the Sertoli cells of the testes. Inhibin is a vital hormone in maintaining reproductive health and fertility. This hormone is produced in response to follicle-stimulating hormone and works by reducing the levels of follicle-stimulating hormone. Inhibin works in contrast to activin (a hormone that increases the level of follicle-stimulating hormone). Inhibin occurs as inhibin A and inhibin B. Lower levels of Inhibin B is a marker for male infertility. Inhibin is vital for sperm production and sperm count.

 

 

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