Male Hormones – FSH, LH and Inhibin
The journey of the hormones related to the male reproductive system begins in the brain. As discussed in our previous blog, the Hypothalamus (HPG axis) plays a major role in sending the signal to the pituitary gland to produce hormones. We all are very familiar with the pituitary gland as it is the Master Gland of the body which produces and controls many hormones throughout the body. The pituitary gland has two parts viz anterior and posterior lobes. We are going to focus on anterior pituitary lobe, as it is responsible for the production of the hormones related to the male reproductive system.
The Hypothalamus produces the GnRH Gonadotropin hormone into the blood vessels, which in turn stimulates the anterior pituitary gland to produce two important hormones called Follicle Stimulating hormone (FSH) and Luteinizing hormone (LH), each of which have separate functions. FSH and LH travel to the testicles via blood vessels and enters into the bloodstream.
FSH (Follicle Stimulating Hormone) regulates the growth, development, pubertal maturation and reproductive functions of the body. FSH works together with the Luteinizing hormone (LH) to produce testosterone, which plays a major role in the development of the male reproductive organs such as testes and prostate gland and the external sexual characteristics of men such as increased muscle and bone mass and secondary sexual characteristics.
Normal Levels of FSH and LH
Hormone levels can be diagnosed by a simple blood test. The normal range of the FSH in adult males is 1.5 – 12.4 mIU/mL and for LH is 1.7-8.6 mIU/mL.
Increase in the FSH level indicates that the testicles are not functioning well. There are various reasons for the malfunctioning of the testes.
If the levels of FSH are low, it could be due to a problem with the pituitary gland although this is less common in occurence.
Similarly, when LH levels are high in men, it means the improper functioning of the testes and if the levels are low, something is wrong with either hypothalamus or the pituitary gland.
Increase in the FSH levels indicates that the normal feedback from the gonad (testes) is absent which may lead to unrestricted pituitary FSH production, results in an indication of sub-fertility or infertility. In men, high FSH levels are due to the primary testicular failure (meaning the ability of the testicles to produce the sperm and the male hormone testosterone). This may be the result of either the developmental defects in testicular growth or injury. It is also an indication of the Klinefelter syndrome (presence of two or more XX Chromosome) or a genetic disorder.
LH targets the Leydig cells in the seminiferous tubules and produces testosterone whereas FSH targets the Sertoli cells in the seminiferous tubules and produces protein called Androgen Binding Protein (ABP) which binds to the androgen receptor and produces the androgen testosterone and also the other hormone called Inhibin.
When testosterone levels rise beyond the normal levels, there is a negative feedback mechanism to inhibit both FSH and LH to slow down the production of testosterone. In such cases, FSH will be controlled by the hormone inhibin by sending a negative feedback signal to the pituitary gland whereas LH sends a signal to the pituitary gland and to hypothalamus as well to stop testosterone production.
This inhibin hormone inhibits the release of the hormones and slows down the process of spermatogenesis, so when the sperm count reaches the minimum count, the sertoli cells stops the action of inhibin, so that the sperm count starts to increase automatically. This is how the regulation of the hormones takes place in the human body related to male reproductive system.
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