Molecular Science, Biology, Health, and Pathophysiology of testosterone
Testosterone. The amazing “male” sex hormone develops sexual characteristics in males and generates sexual drive (libido). It is mostly associated with men and rightfully so because it is the primary male sex hormone BUT females have it too!
Apart from its sexual functions, it is responsible for good cognitive, physiological and physical health in males and females.
Introduction
Testosterone is the primary sex hormone in males. It was discovered in May 1995 by Ernst Laquer, a Dutch scientist working with the Organon Group (1). The hormone is responsible for the development of testes and penis, sperm production, libido (sex drive), and facial and pubic hair, among other functions. The pituitary gland in the brain is responsible for controlling the production of testosterone in the testes. (2)
Chemical composition
Cholesterol is used to synthesize testosterone. This does not necessarily mean that a high level of cholesterol will produce more testosterone. The pituitary gland controls the production of testosterone. (2)
Major functions
i. Development of the testes and penis
Testosterones influence the growth of the penis. This is possibly due to the expansion of the extracellular supportive tissue. (3)
The growth of the testes is mostly due to the expansion and growth of germ cells in the seminiferous tubule. This is triggered by androgens (testosterone). (4)
ii. Sperm production
Sperms are produced in the testicles. Germ cells in seminiferous tubules of the testicles are turned into sperm by hormones such as testosterone. The germ cells divide and change shape until they are tadpole-shaped. (5)
Follicle-stimulating hormone (FSH) and Luteinizing hormone (LH) are produced by the pituitary gland. FSH is responsible for spermatogenesis (sperm production). LH is the stimulant for testosterone production. Testosterone is essential to continue sperm production. (6)
iii. Libido (sex drive)
Sex drive and testosterone have a strong relation in men at the population level. Low testosterone levels have been shown to reduce libido in aging men. (7)
Testosterone’s role in promoting libido may be aided by the increased release of dopamine (reward hormone). (8)
iv. Facial and pubic hair
During puberty, hair on the pubic area and facial hair start to grow. This is a sign that the male child is developing into an adult. Hair grows under the armpit and may grow on the chest. Hair on arms and legs may thicken. Low levels of testosterone may cause loss of body hair. (9)
v. Voice depth
During puberty, the voice of boys cracks up. This is because their voice is increasing in-depth due to the hormonal activities in their body. High testosterone level is associated with a deep voice in men. (10)
vi. Muscle growth and strength
Testosterone has a vital role in stimulating muscle growth. Testosterone stimulates the increase of muscle protein synthesis, which increases muscle mass. (11)
It is also important for muscle strength, body composition and physical functions. (12)
vii. Bone growth and strength
Androgens (testosterone) protect the bone, hence enhancing its strength. They regulate the production of bone-resorbing cells, playing a vital role in bone growth. (13) (14)
Physiological Processing
The hypothalamus gland secretes GnRH, which travels to the anterior pituitary, which secretes FSH and LH. These hormones travel through the blood and act as receptors in the gonads. LH is responsible for stimulating testosterone production. Testosterone regulates its production using negative feedback. It signals back to the hypothalamus and anterior pituitary to suppress secretion and absorption of GnRH, respectively.
Leydig cells in the testes turn cholesterol into testosterone. Initially, LH regulates this process. Dehydroepiandrosterone (DHEA) and androstenedione act as intermediaries in this process.
Androstenedione is converted to testosterone by an enzyme called 17-beta-hydroxysteroid dehydrogenase. The majority of testosterone is bound to plasma proteins i.e., albumin and sex-hormone-binding-globulin. This majority is surplus supply for the body. The small amount of testosterone in the bloodstream act at the level of tissues, bones, muscles and prostate gland.
Dehydroepiandrosterone is produced at the cellular level by converting testosterone. It binds to the cell receptors and regulates protein expression. (15)
Emotional aspects of testosterones
Just like many other hormones, testosterone improves your energy and are responsible for your emotions. It is not only responsible for sex drive but also for intimacy in a relationship.
Low levels of androgen cause low libido. Low levels of estrogens can cause vaginal dryness, night sweats and hot flashes.
It is recommended to check hormone levels if any of these symptoms occur. Because this is one of the reasons that relationships don’t work. (16)
Testosterone in puberty
Testosterones play an essential role in development and growth. Puberty is when the body experiences a growth spurt and sexual characteristics start to appear.
The boys’ muscles mass increases, gain height, shoulder and chest widen. They experience frequent erections, and they start to ejaculate. Facial and pubic hair growth and their voices deepen.
Testosterone in Females
In females, testosterone is produced in the ovaries. Unlike males, they are quickly converted into estrogens.
Testosterones have various functions in the female body:
i. It maintains healthy bones and helps in bone growth.
ii. It minimizes the risk of breast cancer & maintains healthy breasts. (17) It helps increase fertility by developing follicles, which hold and release eggs during ovulation. (18)
iii. Some studies show a correlation between libido and testosterone levels in females, but the evidence is weak. (19) Excess of testosterone in females can lead to irregular mensural cycles and, in some cases, stop menstruation altogether.
iv. Increased hormone levels may cause the natural lubrication of the vagina to decrease. It may also reduce the resilience of the vaginal tissues. This results in tears in the vaginal tissues. (20)
Abnormal testosterone levels
Testosterone deficiency can cause low sex drive, low energy and depression. It can cause bone fragility, a decrease in muscle mass and strength. Dry skin and male pattern baldness may be symptoms of low testosterone levels.
Excess of testosterone can also result in health problems. Excess sweating and acne may indicate spiked T levels. Abnormally high testosterone levels may lead to abnormal blood pressure. Excess body hair and male pattern baldness on the scalp may be due to too much testosterone. Irritability, anxiety, depression and abnormal libido are symptoms of high testosterone levels.
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