Structural Biochemistry/Testosterone

Testosterone is the primary male hormone created from cholesterol. Although it has significantly presence in males, it is created in the ovaries in female as well. As aging occurs, the amount of testosterone is decreased in the body. The decrease in testosterone leads to the decrease of bone density.

Testosterone is a steroid hormone from the androgen group. In mammals, testosterone is primarily secreted in the testes of males and the ovaries of females, although small amounts are also secreted by the adrenal glands. It is the principal male sex hormone and an anabolic steroid. Testosterone is evolutionarily conserved through most vertebrates, although fish makes a slightly different form called 11-ketotestosterone. In men, testosterone plays a key role in the development of male reproductive tissues such as the testis and prostate as well as promoting secondary sexual characteristics such as increased muscle and bone mass and hair growth. In addition, testosterone is essential for health and well-being as well as preventing osteoporosis. On average, an adult human male body produces about ten times more testosterone than an adult human female body. Females are from a behavioral perspective (rather than from an anatomical or biological perspective), more sensitive to the hormone. However, the overall ranges for male and female are very wide, such that the ranges actually overlap at the low end and high end respectively.

Physiological Effects
Androgens promote protein synthesis and cell growth in tissues that contain androgen receptors. Testosterone affects the cell in two different ways: virilizing and anabolic. Anabolic effects increases bone density, bone maturation, and increase in muscle mass and strength. Androgenic effects are maturation of the sex organs, particularly in the size of the penis and the forming of the scrotum in the fetus and after birth, usually during puberty which deepens the voice, growth of hair.

Prenatal Effects
The prenatal androgen occur in 2 different stages. First is the genital virilization which is the midline fusion, scrotal thining, rugation, and phallic enlargement. The second is the development of prostate and seminal vesciles. In the second trimester androgen levels are associated with gender characterization. This period has also known to affect the femininity or masculinity of the fetus and how it can be further predicted to have feminine or masculine behaviors. During pregnancy a mother's testosterone levels the behavior more than the fetusus testosterone level.

Pre-peripubertal Effects
Pre-peripubertal Effects are the first effects that are observed when androgen levels are raised. This usually occurs at the end of childhood and is seen in both girls and boys.
 * Axillary Hair
 * Growth Spurt or accelerated bone maturation
 * Facial Hair
 * Body odour
 * Acne or increase oiliness on skin
 * The appearance of pubic hair

Pubertal Effects
Pubertal effects happen when androgen levels are usually higher than normal.
 * Appearance of Adams apple
 * Broader shoulders as the rib cage expands
 * Deeper voice
 * Remodeling of facial bone contours
 * Increased in muscle mass and strength
 * Leg hair
 * Chest Hair and perianal hair
 * Pubic hair extends to the thighs
 * Increased lido and erection or clitoral engorgement
 * clitoromegaly
 * enlargement of the sebaceous glands
 * Acne
 * Axillary hair
 * Complete bone maturation

Biological Uses

 * Testosterone regulates the thromboxane receptors and platelets.
 * It also maintains muscle trophism
 * Also regulates acute hypothalamic pituitary adrenal axis (HPA) response
 * Testosterone is also necessary for normal sperm growth
 * Activates genes in sertoli cells
 * Promotes differentiation of spermatogonia

Reference: Berg, Jeremy M.; Tymoczko, John L.; Stryer, Lubert. Biochemistry. 7th ed. New York, 2012.