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W. Bushong, Ph.D., LMFT Richard A. Martin, Jr., M.D., FACEP Kimberly L. Westwood, CPE, CCE et al. |
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Specialists in the Medical & Psychological Aspects of Transgender Health Care |
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The Biochemistry of Gender Since we are concerned with hormonal reassignment, defining the term, hormone, is an appropriate place to begin. Hormones are substances, usually a peptide or steroid, produced by one tissue and conveyed by the bloodstream to another to affect physiological activity, such as growth or metabolism. We will be focusing on steroids, in particular, since many steroids are biologically active hormones. This class includes the sex hormones testosterone, estrogen, and progesterone, previously mentioned. Also found in this class are corticosteroids such as cortisone, several forms of vitamin D, cholesterol, and the bile acids. Also included in this somewhat broad class are anabolic steroids which have been linked to abuse by bodybuilders and athletes in an attempt to increase muscle mass and strength. Steroids have a common molecular structure based on four joined carbon rings with hydrogen molecules attached. Steroids differ from one another only in the additional atoms attached to the central structure. The production of hormones are the responsibility of a system of specialized glands referred to as the endocrine system. Numerous steroids are secreted by endocrine glands (ovaries, testes, adrenal glands) and are deposited directly into the blood stream, whereby the blood carries secreted hormones throughout the body. But only target cells (i.e., cell that possess the appropriate receptor) within a tissue/organ are affected by hormonal action. In normal physiology, a domino effect of targeting (and conversion into other substances) play pivotal roles in the function of our organs, and ultimately the physical characteristics we possess. Examples include the function of the uterus in the female, which is influenced by the estrogen and progesterone produced by the ovaries, her chief source of sex hormone production. And these hormone glands, the ovaries, were in turn influenced by her pituitary gland (the master gland located at the base of the brain). The target organ might not be what we normally consider an organ, such as the hair follicle. The tiny hair manufacturing organs produce facial, body, and scalp hair. Facial hair growth, in men and women, is a result of androgen production. The term androgen refers to any hormone or substance that creates male-like symptoms or physical changes. The testes (testicles) of the male and the adrenal glands found in both sexes contribute to androgen production. With the matter of facial hair, testosterone is the hormone that leaves the bloodstream where it acts on its target organ, in this case, the hair follicle. Naturally, there are other targets besides the hair follicle. Ultimately, the hormone is metabolized, usually by the liver, after which it is excreted in the urine. But facial hair growth, while not so simple, is a good example of hormonal conversion. Here the androgenizing (masculinizing or virilizing) effect occurs from the conversion of testosterone to DHT (dehydrotestosterone) by the 5-alpha-reductase enzyme. This conversion occurs in the hair follicle itself. DHT is the principal androgen acting on the hair follicle. In other words, DHT not testosterone is directly responsible for beard growth, excess body hair and balding. Clearly hormones are responsible for a wide variety of human function including our growth and development, reproduction, and of particular importance in this context, our gender characteristics.
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