Hormones: Testosterone

Testosterone is a hormone which is responsible for many of the physical characteristics specific to adult males.It plays a key role in reproduction and the maintenance of bone and muscle strength.


Alternative names for testosterone

Testo (brand name for testosterone formulations); 4-androsten-17β-ol-3-one.


What is testosterone?

Testosterone is produced by the gonads (by the Leydig cells in testes in men and by the ovaries in women), although small quantities are also produced by the adrenal glands in both sexes. It is an androgen, meaning that it stimulates the development of male characteristics.

Present in much greater levels in men than women, testosterone initiates the development of the male internal and external reproductive organs during foetal development and is essential for the production of sperm in adult life. This hormone also signals the body to make new blood cells, ensures that muscles and bones stay strong during and after puberty and enhances libido both in men and women. Testosterone is linked to many of the changes seen in boys during puberty (including an increase in height, body and pubic hair growth, enlargement of the penis, testes and prostate gland and changes in sexual and aggressive behaviour). It also regulates the secretion of luteinising hormone and follicle stimulating hormone. To effect these changes, testosterone is often converted into another androgen called dihydrotestosterone.

In women, testosterone is produced by the ovaries and adrenal glands. The majority of testosterone produced in the ovary is converted to the principle female sex hormone, oestradiol.

How is testosterone controlled?

The regulation of testosterone production is tightly controlled to maintain normal levels in blood, although levels are usually highest in the morning and fall after that. The hypothalamus and the pituitary gland are important in controlling the amount of testosterone produced by the testes. In response to gonadotrophin-releasing hormone from the hypothalamus, the pituitary gland produces luteinising hormone which travels in the bloodstream to the gonads and stimulates the production and release of testosterone.

As blood levels of testosterone increase, this feeds back to suppress the production of gonadotrophin-releasing hormone from the hypothalamus which, in turn, suppresses production of luteinising hormone by the pituitary gland. Levels of testosterone begin to fall as a result, so negative feedback decreases and the hypothalamus resumes secretion of gonadotrophin-releasing hormone.

What happens if I have too much testosterone?

The effect excess testosterone has on the body depends on both age and sex. It is unlikely that adult men will develop a disorder in which they produce too much testosterone and it is often difficult to spot that an adult male has too much testosterone. More obviously, young children with too much testosterone may enter a false growth spurt and show signs of early puberty and young girls may experience abnormal changes to their genitalia. In both males and females, too much testosterone can lead to precocious puberty and result in infertility.

In women, high blood levels of testosterone may also be an indicator of polycystic ovary syndrome. Women with this condition may notice increased acne, body and facial hair (called hirsutism), balding at the front of the hairline, increased muscle bulk and a deepening voice.

There are also several conditions that cause the body to produce too much testosterone. These include androgen resistance, congenital adrenal hyperplasia and ovarian cancer.

The use of anabolic steroids (manufactured androgenic hormones) can lead to a perceived high level of testosterone by the hypothalamus, resulting in reduced luteinising hormone secretion from the pituitary gland and, in turn, a decrease in the amount of testosterone produced within the testes, while artificial testosterone levels remain high.  In men, prolonged exposure to anabolic steroids results in infertility, a decreased sex drive, shrinking of the testes and breast development. Liver damage may result from its prolonged attempts to detoxify the anabolic steroids. Behavioural changes (such as increased irritability) may also be observed. Undesirable reactions also occur in women who take anabolic steroids regularly, as a high concentration of testosterone, either natural or manufactured, can cause masculinisation (virilisation) of women.

What happens if I have too little testosterone?

If testosterone deficiency occurs during foetal development, then masculinisation of the foetus will fail to occur normally and this may give rise to disorders of sex development. If testosterone deficiency occurs during puberty, a boy’s growth may slow and no growth spurt will be seen. The child may also fail to develop full sexual characteristics (hypogonadism) associated with men undergoing puberty, including development of pubic hair, growth of the penis and testes and deepening of the voice. Around the time of puberty, boys with too little testosterone may also have less than normal strength and endurance, and their arms and legs may continue to grow out of proportion with the rest of their body.

In adult men, low testosterone may lead to a reduction in muscle bulk, loss of body hair and a wrinkled ‘parchment-like’ appearance of the skin. Testosterone levels in men decline naturally as they age. In the media, this is sometimes referred to as the male menopause (andropause).

Low testosterone levels can cause mood disturbances, increased body fat, loss of muscle tone, inadequate erections and poor sexual performance, osteoporosis, difficulty with concentration, memory loss and sleep difficulties. Current research suggests that this effect occurs in only a small group of ageing men. However, there is a lot of research currently in progress to find out more about the effects of testosterone in older men and also whether the use of testosterone replacement therapy would have any benefits.

Comments

Post a Comment

Popular posts from this blog

How does cerebral hypoxia cause euphoria?

The mechanism by which the conscious feeling of euphoria is felt is still unknown. Due to the multiple methods by which euphoria can occur it is likely a 'natural' state of the brain that can be triggered either naturally or unnaturally. It is also likely that it occurs in the same brain regions responsible for mood. https://en.wikipedia.org/wiki/Reward_system You'll note that many of the structures connected to the reward system are glutamatergic interneurons. This means that excess glutamate can trigger the reward system to produce euphoric feelings. In cerebral hypoxia the lack of oxygen results in a lack of energy for the cell. Mainly this results in the switching off of the sodium / potassium pump. A nerve cell fires by moving sodium outside the cell and potassium inside the cell to create concentration gradients, that are then reversed during an action potential. If the pump does not have oxygen then this mechanism stops. This results in an increase in e...
Read more

Negative Health Effects of Artificial Blue Light at Night And What You Can Do About It

Image
Nighttime  blue light  exposure can derange the  circadian rhythm . It is a culprit behind many modern chronic health issues, including  obesity , metabolic syndrome, and cancer. On the other hand,  blue light  exposure during the day is very beneficial. Read this post to learn how to hack your  blue light  exposure for your benefit. What is Blue Light? Light is  electromagnetic radiation  of a variety of wavelengths within the electromagnetic spectrum. There is both visible and non-visible light. Non-visible light includes ultraviolet ( UV ) and  infrared  light, while visible light includes the whole spectrum of the rainbow, including blue light. Within the visible light spectrum, each wavelength is represented by a color. Of all the colors of the visible light spectrum, blue light (wavelength 446 – 477 nm) has the strongest impact on physiology and  circadian rhythm  because our pigments react to this w...
Read more

Cannabinoids, like those found in marijuana, occur naturally in human breast milk

Woven into the fabric of the human body is an intricate system of proteins known as cannabinoid receptors that are specifically designed to process cannabinoids such as tetrahydrocannabinol (THC), one of the primary active components of marijuana. And it turns out, based on the findings of several major scientific studies, that human breast milk naturally contains many of the same cannabinoids found in marijuana, which are actually extremely vital for proper human development. Cell membranes in the body are naturally equipped with these cannabinoid receptors which, when activated by cannabinoids and various other nutritive substances, protect cells against viruses, harmful bacteria, cancer, and other malignancies. And human breast milk is an abundant source of endocannabinoids, a specific type of neuromodulatory lipid that basically teaches a newborn child how to eat by stimulating the suckling process. If it were not for these cannabinoids in breast milk, newborn children would not k...
Read more