Male Sex Hormones Flashcards
what is testosterone?
a potent androgen
where is testosterone synthesised?
within the leydig cells of testes in males and some adrenal cortex cells in both males and females
what is testosterone responsible for?
the development and maintenance of the male secondary sexual characteristics e.g. hair growth
-activate oestrogen receptors
what two other androgens are synthesised in the adrenal cortex in both genders besides testosterone?
- dehydroepiandrosterone (DHEA) - causes early pubic hair growth in boys and girls
- Androstenedione
- both are weak androgens
what is testosterone metabolised to in men?
- dihydrotetosterone with the use of the enzyme 5alpha-reductase (types 1&2)
- this is an active testosterone metabolite
what is testosterone metabolised to in women?
- estradiol with the use of aromatase enzyme.
- estradiol is an active metabolite of testosterone
what does testosterone do in men?
- stimulates testes enlargement and male accessory organ
2. Stimulates development of male secondary sex characteristics
what are the male secondary sex characteristics?
- increased body hair growth
- Enlargement of the larynx and thickening of the vocal cords
- Thickening of the skin
- Muscle growth, widening of shoulders, narrowing of waist
- Thickening and strengthening of bones
how does DHT work?
- binds to cytoplasmic androgen receptors which promotes release of heat shock protein.
- it then migrates to the nucleus where it binds to specific regions of DNA that contain androgen response elements (ARE)
- this drives the expression of genes that determine male phenotype
what is the effect of androgen receptor insensitivity in women?
the women develop normally with very sparse pubic and axillary hair
where are male reproductive hormones released?
- hypothalamus
- anterior pituitary glad
- testes
what is the function of male reproductive hormones?
– Development of sperm cells
– Development of secondary sex characteristics
In both genders the brain controls reproduction through which hormones?
- GnRH (gonadotropin releasing hormone)
2. Pituitary gonadotropins (e.h. FSH and LH)
where is GnRH produced?
by the hypothalamus
what 2 hormones does GnRH drive the release of from the anterior pituitary?
FSH and LH
how does LH work?
Luteinising hormone works to activate leydig cells in seminiferous tubules evoking testosterone release into the bloodstream
how does FSH work?
- acts on Sertoli cells which release androgen binding protein (ABP) into the lumen
- this binds to testosterone leading to its accumulation in seminiferous tubules
- FSH also stimulates inhibin production
what effect does a very high testosterone level have?
it drives spermatogenesis
what does inhibin do to the body?
- mediates the negative feedback to suppress FSH and LH release.
- testosterone also suppresses them
what 3 things does testosterone suppress the production of?
- GnRH
- LH
- FSH
what are exogenous androgens?
the anabolic steroids used by body builders
what is the effect of repeated use of an anabolic steroid?
- causes abnormally high levels of androgen so GnRH, FSH and LH release is suppressed
- this suppresses endogenous testosterone production
- FSH can’t stimulate androgen binding protein (ABP) so spermatogenesis is inhibited
what is abnormally high testosterone metabolised to in anabolic steroid users?
oestrogen
what is the effect of withdrawing from the exogenous anabolic steroid?
causes gynecomastia (an increase in the amount of breast gland tissue in boys or men)
what happens to penile arterioles to cause an erection?
they vasodilate to allow more blood through hence causing an erection
what is the effect of testicular failure?
causes:
- infertility
- hypogonadism (reduction or absence of hormone secretion or other physiological activity of the testes or ovaries)
- and a lack of 2nd sexual characteristics
- can trat 2nd sexual characteristics but not fertility
what is hypogonadotropic hypogonadism?
Infertility + associated hypogonadism and lack of 2nd sexual characteritics
-however, can treat 2nd sexual characteristics and improve fertility
what is primary hypogonadism?
issues with the testes themselves
what is secondary hypogonadism?
issues with the pituitary/hypothalamus
what is the effect of hypogonadism in foetal life?
-causes impaired development of male genitalia
what is the effect of hypogonadism during puberty?
delays puberty and causes longer limbs in relation to the rest of the body
what is the effect of hypogonadism during adult life?
as you age, testosterone levels drop causing erectile dysfunction, infertility, less beard and body hair, development of breast tissue
what are the testosterone replacement therapies available?
- exogenous testosterone given by injection
2. transdermal patches of gels.
