This document provides an overview of testosterone, including its structure, secretion, effects, and mechanisms of action. Testosterone is the principal male sex hormone. It is secreted primarily by the testes in males and the ovaries in females. Testosterone promotes the development of male secondary sex characteristics, increases muscle and bone mass, and supports male sexual functions and spermatogenesis. It works primarily by binding to androgen receptors in cells or being aromatized into estradiol. Abnormalities in testosterone levels or signaling can result in various medical conditions.

1. Welcome

3. Testosterone Hormone
C19H28O2
By : Ibrahim Mahmoud Gehad Fathy

4. Introduction :
 Testosterone is a steroid hormone from the androgen group and is found in
mammals, reptiles ,birds ,and other vertebrates. In mammals, testosterone
is secreted primarily by the testicles 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.
 On average, in adult males, levels of testosterone are about 7–8 times as
great as in adult females
 but, as the metabolic consumption of testosterone in males is greater, the
daily production is about 20 times greater in men.
 Females are also more sensitive to the hormone !

5. Secretion
 1- From interstitial cells of Leyding between seminiferous tubules
 “ about 20% of testicular mass “
 Small amounts are secreted by adrenal glands

6. Overall Health effects :
 In general, androgens promote protein synthesis and growth of
those tissues with androgen receptors. Testosterone effects can be
classified as anabolic and virlizing
 Anabolic effects include growth of muscle mass and strength,
increased bone density and strength, and stimulation of linear
growth and bone maturation.
 Androgenic effects include maturation of the sex organs,
particularly the penis and the formation of the scrotum in the fetus,
and after birth (usually at puberty) a deepening of the voice,
growth of the beard and axillary hair. Many of these fall into the
category of male secondary sex characteristics.

7. Mechanism of Action :

8. 97% bound to protein in plasma
3 % free
 Two main cellular mechanism of action :
 1- androgen receptor (directly or as DHT)
 Free testosterone (T) is transported into the cytoplasm of target tissue
cells, where it can bind to the androgen receptor, or can be reduced
to 5α-dihydrotestosterone (DHT) by the cytoplasmic enzyme 5-alpha
reductase. DHT binds to the same androgen receptor even more
strongly than testosterone, so that its androgenic potency is about 5
times that of T. The T-receptor or DHT-receptor complex undergoes a
structural change that allows it to move into the cell nucleus and bind
directly to specific nucleotide sequences of the chromosomal DNA. The
areas of binding are called hormone response elements (HREs), and
influence transcriptional activity of certain genes, producing the
androgen effects.

9. 2nd mechanism
 In tissues like :
 Brain
 Bones
 It aromatization into stradiol “ female sex hormone “
 In bone helps in ossification , union of epiphysis
 In brain helps feedback signals in hypothalamus “ LH secr. “

10. Function : A- Sexual Function
 1-During intrauterine life : secreted from genital ridge
 Help in formation of male sex characters as :
 Formation of penis , scrotum , seminal vesicles , prostate , male
genital ducts
 Suppretion of female genital organs
 Influence the descent of testes into scrotum since 2nd month of
pregnancy

11. 2-early infancy : least understood , increases in first weeks then falls again
helps in brain development
3- before and at puberty :
appearance of male secondary sex characters :
- growth of hair over pubis , extension towards umbilicus , on face and
chest , axillary , leg hair
- growth of sex organs : testes , scrotum , penis , prostate
- deepness of voice due to hypertrophy of larynx
- male body type : narrow pelvis and wide shoulders
-males sexual behavior associated with adulthood like desire to opposite
sex
- increase muscle strength
-appearance of adam’s apple
- growth of jaw , braw , chin .
4- in adults
1- spermatogenesis
2- baldness : decrease hair growth at top of the head , provided genetic
background

12. Metabolic effects
 1- increases basal metabolic rate
 2- anabolic to protein : increases muscle bulk and strength
 3- on CHO : increases glycogenolysis and increase glucose uptake
by cells
 4- reduction f ca2+ and po4
 5- union of epiphysis
 6- stimulate erythropoiesis
Degraded by conjugation in liver to excrete in urine or in bile salts

13. Control :
 1- Luteinizing hormone : the hormone secretion is stimulated by LH
 2- GnRH : LH secretion is stimulated by “ GnRH “ from hypothalamus
to the ant. Pituitary
 3- _ve feedback mechanism : mainly by the testosterone on the
hypothalamus and weaker effect on the ant. Pituitary
 Other factors affects secretion : weight loss , zinc deficiency , aging
, dominance challenge , sleep , training , licorice , antiandrogens

15. Abnormalities : a- hypogonadism in
male
 1- during fetal life : when the testes arenot functioning , none of
male characteristics appear , instead female organs are formed
 2- if boy loses his testes before puberty :
 A state of eunichism : infantile sex organs and sex characters
 Slightly tall because of slower union of epiphysis
 3- if a man is castrated after puberty
 - secondary sexual characters aren’t affected
 -decreased sexual desire and sterility
 -accessory sexual organs are gradually dysfunctioned
 -FSH & LH are increased due to –ve feedback mechanism

16. B- adiposogenitial syndrome, Frolich’s
syndrome,hypothalamic eunuchism
 Hypogonadism due to genetic inability of hypothalamus to secrete
normal amount of Gnrh & abnormality of feeding of center of
hypothalamus leads to obesity with eunuchism

18. For fun facts :
1-A mother's testosterone level during pregnancy is correlated with her daughter's sex-typical behavior as
an adult, and the correlation is even stronger than with the daughter's own adult testosterone level.
2-Falling in love decreases men's testosterone levels while increasing women's testosterone levels
3- Fatherhood also decreases testosterone levels in men, suggesting that the resulting emotional
and behavioral changes promote paternal care.
4- men who produce less testosterone are more likely to be in love , married while those produce
more are likely to be divorced .
5-It has been found that when testosterone and endorphins in ejaculated semen meet the cervical
wall after sexual intercourse, females receive a spike in testosterone, endorphin, and oxytocin
levels, and males after orgasm during copulation experience an increase in endorphins and a
marked increase in oxytocin levels.
6-Testosterone levels play a major role in risk-taking during financial decisions.
7-As testosterone affects the entire body (often by enlarging; males have bigger hearts, lungs, liver,
etc.), the brain is also affected by this "sexual" differentiation” as males brains are larger and have
more myelinated fibers

19. The "evolutionary neuroandrogenic theory“: focuses on the hormone testosterone as a
factor influencing aggression and criminality and being evolutionarily beneficial during
certain forms of competition. In most species, males are more aggressive than females.
Castration of males usually has a pacifying effect on their aggressive behavior. In
humans, males engage in crime and especially violent crime more than females.
Testosterone in the presence of a slow-growing cancer is assumed to increase its growth
rate.
Medical uses :reducing infertility, correcting erectile dysfunction, correcting
osteoporosis, encouraging penile enlargement, encouraging height growth,
encouraging bone marrow stimulation and reversing the effects of anemia, and
appetite stimulation.
There are many routes of administration for testosterone. Forms of testosterone for
human administration currently available include injectable (such as testosterone
cypionate or testosterone enanthate in oil), oral, buccal, transdermal skin patches,
transdermal creams, gels.
A number of lawsuits are currently underway against testosterone manufacturers,
alleging a significantly increased rate of stroke and heart attack in elderly men who use
testosterone supplements.

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