Boosting Brain Health [ABC: 5-23-2011]Subscribe for daily health news. Like/Dislike, Favorite, Comment, Embed on Blog, Facebook Share, and Tweet this video. Get the word out on this video. - Tuesday May 24 2011 12:00 am http://en.wikipedia.org/wiki/Testosterone Testosterone is a steroid hormone from the androgen group and is found in mammals, reptiles, birds, and other vertebrates. 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. 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, bone mass and the growth of body-hair. In addition, testosterone is essential for health and well-being as well as the prevention of osteoporosis. On average, an adult human male body produces about ten times more testosterone than an adult human female body, but females are more sensitive to the hormone. Testosterone is conserved through most vertebrates, although fish make a slightly different form called 11-ketotestosterone. Its counterpart in insects is ecdysone. These ubiquitous steroids suggest that sex hormones have an ancient evolutionary history. In general, androgens promote protein synthesis and growth of those tissues with androgen receptors. Testosterone effects can be classified as virilizing and anabolic, although the distinction is somewhat artificial, as many of the effects can be considered both. Testosterone is anabolic, meaning it builds up bone and muscle mass. Testosterone effects can also be classified by the age of usual occurrence. For postnatal effects in both males and females, these are mostly dependent on the levels and duration of circulating free testosterone. the prenatal androgen effects occur between 4 and 6 weeks of the gestation. Early infancy androgen effects are the least understood. In the first weeks of life for male infants, testosterone levels rise. The levels remain in a pubertal range for a few months, but usually reach the barely detectable levels of childhood by 4--6 months of age. The function of this rise in humans is unknown. It has been speculated that 'brain masculinization' is occurring since no significant changes have been identified in other parts of the body. Surprisingly, the male brain is masculinized by testosterone being aromatized into estrogen, which crosses the blood-brain barrier and enters the male brain, whereas female fetuses have alpha-fetoprotein which binds up the estrogen so that female brains are not affected. Pre- Peripubertal effects are the first observable effects of rising androgen levels at the end of childhood, occurring in both boys and girls. Pubertal effects begin to occur when androgen has been higher than normal adult female levels for months or years. In males, these are usual late pubertal effects, and occur in women after prolonged periods of heightened levels of free testosterone in the blood. Adult testosterone effects are more clearly demonstrable in males than in females, but are likely important to both sexes. Some of these effects may decline as testosterone levels decrease in the later decades of adult life. As testosterone affects the entire body (often by enlarging; men have bigger hearts, lungs, liver, etc. ), the brain is also affected by this 'sexual' differentiation; the enzyme aromatase converts testosterone into estradiol that is responsible for masculinization of the brain in male mice. In humans, masculinization of the fetal brain appears, by observation of gender preference in patients with congenital diseases of androgen formation or androgen receptor function, to be associated with functional androgen receptors. There are some differences between a male and female brain (possibly the result of different testosterone levels), one of them being size: the male human brain is, on average, larger. In a Danish study from 2003, men were found to have a total myelinated fiber length of 176,000 km at the age of 20, whereas in women the total length was 149,000 km. However, women have more dendri code pour embarquer la vidéo : >>> http://www.youtube.com/embed/Fs8yf1I69iM <<< |