Testosterone is generally regarded as a ‘male hormone’ belonging to the androgen family, that stimulates the development of sexual traits and maintains a stable environment for sperm production. The hormone derives its name from ancient Greek terminologies ‘andros’ (man) and ‘gen’ (to produce), even though it’s normally regarded as the male hormone, testosterone is also found in the female hormone system. The production of testosterone is primarily made by the testes; ovaries and adrenal cortex also contributes in its production. Apart from sexual functions, testosterone also plays a major role in preserving other body functions, which includes- metabolism, cardiovascular activities, bone and muscle development etc.. Here in this article we will discuss the synthesis of testosterone.

Synthesis of Testosterone

The hormone testosterone is one of the essential parts of the hormone system of our body. As testosterone is grouped with steroids, its synthesis is also done with the steroidogenesis process. The synthesis of testosterone is generally segregated in two processes
Biosynthesis- This step involves the molecular and biochemical mechanisms responsible for the synthesis of testosterone.
Regulation: Regulation is majorly concerned with  the hormonal control, it depicts the significant link that must exist between regulatory glands and production glands to fabricate testosterone.

Biosynthesis

The biosynthesis of testosterone are primarily made from cholesterol. This complex mechanism includes a series of genes and biochemical compounds. The steps of biosynthesis are described stepwise below-

  • The preliminary step with which the biosynthesis of testosterone starts involves a cholesterol side chain cleavage gene (CYP11A) that provides oxidative cleavage of the choleterol’s sidechain. This gene is a member of cytochrome P450 oxidase, which localizes to mitochondrial inner membrane and catalyzes the conversion of cholesterol to pregnelone.
  • In the following step, another enzyme of cytochrome P450oxidase family localized in the endoplasmic reticulum, CYP17A1 (monoosygenase) removes two extra carbon atoms and yields multiple C19 steroids. Moreover, the pregnalone that is formed in the previous step gets oxidized to form androstenedione/progesterone by the catalyzing effect of 3-β-HSD (hydroxysteroid dehydrogenase)
  • The terminal step of this process is a rate limiting step,  the keto group in 17th carbon position of androstenedione is reduced by 17-beta hydrosysteroid dehydrogenase (17-β-HSD) to finally produce testosterone.

This is the summary of the complex biochemical process that occurs in our body to produce testosterone

The Leydig cells testicles contribute the major portion in testosterone production. The production of testosterone is also contributed by the thecal cells in the woman’s ovaries, by the placental cells, also by the cells present in the adrenal cortex and skin of both males and females, though the amount is minimal.

Regulation

The process of synthesizing testosterone is regulated by a delicate network of endocrine hormones. The process that the testicles utilize in order to produce testosterone appears similar to Rube Goldberg contraption. By the following steps the regulatory network for the testosterone synthesis id described-

  • Brain is the control center for every action in our body, likewise this regulatory network also starts with the brain. When the gland hypothalamus detects the need of testosterone by our body or any drop in testosterone levels, the hormone gonadotropin releasing hormone is secreted by the gland. The hormone GRH (gonadotropin-releasing hormone) travels to pituitary gland; another regulatory gland present in the back of our brain.
  • When the pituitary gland perceives the presence of GRH (gonadotropin-releasing hormone), it starts secreting two other stimulating hormone:  luteinzing hormone (LH) and follicle-stimulating hormone (FSH). The Follicle stimulating hormone (FSH) and luteinizing hormone (LH) after being released into the bloodstream travel to the testicles.
  • When the Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH) travels through the bloodstream and comes in contact with the pair of testicles, two events gets kicked off. The Follicle Stimulating Hormone (FSH) stimulates the production of sperm, while the Luteinizing Hormone (LH) influences the Leydig cells that are present in the testicles to produce more testosterone.
  • Now, after getting stimulated by the Luteinizing Hormone (LH) a whole series of complex events are orchestrated in the testicles, the Leydig cells present in the testicles start the conversion of cholesterol into testosterone. Though it may sound surprising, the key ingredient that is required for the synthesis of testosterone is cholesterol. The Leydig cells utilize the free cholesterol that floats in our blood, that comes from our heavy diet (especially meat, eggs etc.) to meet the testosterone requirement. If the cholesterol levels are not adequate, the testicles play the part of producing cholesterol, which turn into testosterone by the Leydig cells. But this may pose a serious threat, as the functioning capacity of the Leydig cells gets inhibited if the production of testosterone is majorly based on cholesterol produced by our testicles. For this reason a balanced diet of all necessary ingredients is essential.

Once Testosterone production is complete, it’s released into the bloodstream. Immediately after getting released into bloodstream, most of the testosterone gets attached to sex hormone binding globulin (SHBG) and albumin and becomes biologically inactive. Only a small percentage that remains unbound circulates throughout the body and maintains the body functions, this is generally referred to as free testosterone. With the production of required testosterone, hypothalamus detects the levels and with co-operation of pituitary gland stops the testosterone production by halting the production of Luteinizing hormone (LH).

This is how testosterone production is regulated by the endocrine hormone system, it is depicted pictorially below:
How is testosterone made in body

Summary

Testosterone, the male hormone that takes part in most of the significant body functions is secreted by the glands present in our body. The complex procedure behind the synthesis portrays its importance. Deficiencies and abnormalities regarding the testosterone levels or disease related to testosterone basically have its roots tied to this process. Further scientific breakthroughs are required to study this procedure to its very core and develop radical solutions.

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