The Biochemistry of Sex Hormones

The Biochemistry of
Sex Hormones
All steroids in the body are formed from acetate, which is a 2-carbon compound. Steroids display a characteristic four-ring system. This steroid carbon skeleton, often referred to as the steroid nucleus, is found in all the steroids described here.

The first step in its conversion to a variety of steroids is the formation of cholesterol, which is a 27-carbon steroid. The formation of cholesterol occurs through a complex, eleven step series of reactions. Cholesterol is by far the most common steroid.  It is found in most animal tissue, with the greatest amount in the tissues of the central nervous system, that being the brain and spinal cord.
With any introduction to the essential nature and importance of cholesterol, it should be noted that the common concern with cholesterol is derived from its excess, whereby it contributes to vascular and heart disease. Cholesterol, in of itself, is absolutely not unhealthy, but essential to life.

The Degradation of Cholesterol
In the next phase, the cholesterol degrades, and in the ensuing process, creates all sex steroids (sex hormones) and corticosteroids.
The variety of steroids created occur from a stepwise degradation of cholesterol: Pregnenolone, progesterone, 17-hydroxypregnenolone, 17-hydroxyprogesterone, and corticosteroids, having 21 carbon atoms, followed by androgens (testosterone and androstenedione), having 19 carbon atoms, and natural estrogens having 18 carbon atoms.

Pregnenolone plays a vital role in the production of all other human sex hormones. It is converted to androgens (male sex hormones), progestins (hormones involved in pregnancy), and estrogens (female sex hormones).
All three of these hormones are in the bloodstream of males and females at all times; the differing concentrations of testosterone, progesterone, and estrogen contribute to the gender characteristics specific to males and females. These hormones are largely produced by the ovaries or the testes, as well as the adrenal glands of both sexes.  As mentioned earlier, the pituitary controls the production of these hormones.
Progesterone is the most important pregnancy hormone. It is produced in the ovaries by the enzymatic oxidation of cholesterol and is responsible for both the successful initiation of a pregnancy and the successful completion of pregnancy. Its initial role is to prepare the uterine mucosa (lining) for reception of a fertilized ovum. When the fertilized ovum is successfully attached to the uterine wall, the progesterone continues to be produced, aiding in the successful development of the fetus and at the same time suppressing further ovulation. The role of steroids in pregnancy had led to research into the uses of these compounds as birth control agents. Initially progesterone itself was studied in this regard, but it was found that the dose required to prevent ovulation is much too large.
Progesterone in turn can be biochemically converted to testosterone, which is found in the testes, and finally to estrone (an estrogen), which incidentally was first isolated from the urine of pregnant women. Both of these steroids play a major role in the development of male and female characteristics. Progesterone can also be converted to cortisone (a corticosteroid found in the adrenal gland), which is responsible for regulating a variety of metabolic processes.
Hormonal Breakdown
The liver plays an important role in hormonal modification and inactivation through its metabolism of both estrogen and testosterone, the latter being largely broken down at its target cells.
Nearly all drugs are modified or degraded in some way in the liver. Oral medications are first absorbed by the gut and transported via portal circulation (a certain amount of blood from the intestine is collected into the portal vein and carried to the liver). At that point, drugs are modified, activated, or inactivated before they enter systemic circulation (the normal blood nourishment that is the major part of the circulatory system). The body's circuitous path to the administration of oral medication lends this process to be described as "requiring a first pass" through the liver versus the rapid access to systemic circulation when drugs are administered parenterally (into the muscle, into a vein, under the skin).
These hormones are effectively handled by the various cells of the body, of particular importance, the cells of the liver, without harm to the individual.  But long term, as well as short term, administration of hormone therapies require careful administration and periodic monitoring to assure good health is maintained. The healthy liver will manage these processes very well.  However, a damaged liver, whether related to substance abuse or infection, does not easily facilitate the necessary breakdown process.

The overall process of hormonal biosynthesis.