Zusammenfassung der Ressource
Male Reproductive Hormones
- Structure of the Testis
- Seminiferous Tubule
- Main structural unit
- Each tubule ~60cm but tightly coiled
- Made of Sertoli cells and germ cells (spermatogonia)
- 600 million germ cells per testis during puberty
- Germ cells migrate from the basement membrane to
the tubule lumen, developing into sperm as they go
- Spermatogonium
- Primary spermatocyte
- Mitosis
- Early spermatids
- Late spermatids
- Sertoli cells engulf remaining cytoplasm from late
spermatids as they leave - leaves residual bodies
- Leydig cells lie between the tubules
- Blood-testis barrier
- Formed by tight junctions between Sertoli cells
- Maintains internal environment of testis
- Keeps high concentration of hormones
- Protects against toxins
- Breaching of the barrier can cause infertility
- Autoimmunity against sperm components
- Function of the Testis
- Spermatogenesis
- Production of male sex hormones - androgens
- Androgen Production
- Steroidogenesis takes place in Leydig cells
- Main androgen is testosterone
- Testosterone production
- Cholesterol
- Pregnenolone (via cholesterol-side chain cleavage by P450scc)
- Progesterone (via 3-beta-hydroxysteroid dehydrogenase)
- 17-alpha-OH-progesterone (via 17-alpha-hydolyase)
- Androstenedione (via 17, 20 lyase)
- Testosterone
- Oestradiol (via CYP19 aromatase)
- 17-alpha-OH-pregnenolone (via 17-alpha-hydroxylase)
- DHEA (via 17,20 lyase)
- Androstenedione (via 3-bet-hydroxysteroid dehydrogenase)
- (via 17-beta-hydroxysteroid dehydrogenase)
- 5-alpha-dihydrotestosterone - 5alphaDHT (via 5-alpha-reductase)
- Converted in peripheral tissues
- Exerts many of the hormonal actions of testosterone
- 17-alpha-OH-progesterone (3-beta-hydroxysteroid dehydrogenase)
- Under hormonal control by the hypothalamo-pituitary-testicular axis
- Acts as a paracrine regulator of spermatogenesis (non-genomic action)
- Acts as a hormone and hormone precursor
- Hormonal Control of Testicular Function
- Controlled by the hypothalamo-pituitary-testicular axis
- Gonadotrophin releasing hormone (GnRH)
released by the hypothalamus in a pulsatile way
- Stimulates release of LH and FSH (only if pulsatile)
- LH (luteinising hormone) regulates Leydig cell function
- Testosterone is released
- Acts on Sertoli cells
- Spermatogenesis
- Hormone functions
- Inhibits LH and GnRH - negative feedback
- FSH (follicle stimulating hormone)
regulates Sertoli cell function
- Sertoli cell inhibits FSH
- Spermatogenesis
- Spermatogenesis occurs at a low
rate in the absence of FSH
- Spermatogenesis is totally dependent on
the high intra-testicular testosterone level
- Sertoli cells produce an androgen binding protein
which retains testosterone in the testicular fluid
- Actions of LH
- AC binds to sigma region of LH, converting ATP to cAMP
- Activation of Protein kinase A
- Activation of StAR (steriodigenic acute regulatory protein)
- Delivers free cholesterol to P450scc
(cholesterol side-chain cleavage enzyme)
- Testosterone production
- Increased cholesterol ester hydrolase
- Increased cholesterol ester
- Increased free cholesterol
- Nuclear effects - increased CYP
(cytochrome P450) gene expression
- Androgens in Blood
- Diurnal variation - testosterone is highest in the morning
- Circulates are bound to sex-hormone binding globulin (SHBG)
- Only 2% are unbound
- Converted to DHT or oestradiol
- Act through the androgen receptor - binds
DHT and testosterone with equal affinity
- Bound receptor binds to androgen response element
on DNA with co-activators and initiates transcription
- Androgen Receptor
- Gene is located on the X-chromosome
- Mutations are X-linked - mother has
50% chance of passing it onto a son
- Androgen insensitivity syndrome is a
spectrum of disorders affecting men
- Androgen Action in Men
- Intra-uterine
- Development of male phenotype
- Development of penis, scrotum, prostate etc.
- Testicular descent into scrotum
- Before descent, testicles are suspended near
kidneys by cranial suspensory ligaments
- Gubernaculum connects skin to epididymis
- Ligament degrades once testis descend
and gubernaculum connects skin to testis
- Inguinal canal contains the vas deferens
- Programming of male behaviour
- Puberty
- Development of male secondary sex characteristics
- Hypertrophy of larynx
- Development of seminal vesicles,
prostate and initiation of sperm production
- Increased muscle mass
- Increased skin thickness and sebum formation
- Development of pubic and axillary hair
- Fusion of epiphyseal plates in long bones
- Adults
- Reproductive effects - maintenance of spermatogenesis,
secondary sex characteristics (beard growth), libido and
feedback inhibition of GnRH secretion
- Metabolic effects - increasing circulating LDL/VLDL
and decreasing HDL, increasing metabolic rate, red
blood cell number, muscle mass and bone density
- Symptoms of deficiency
- Depression, fatigue, loss of libido
- Little facial hair growth, scant body hair
- Muscle weakness, loss of muscle definition
- Small testicles
- Anabolic Androgen Steroid Abuse
- Increased aggression - road rage
- Increased muscle mass
- Acne
- Testicular atrophy and/or infertility
- Liver cancer (if taken orally)
- Oestrogens in Men
- Oestradiol mediates many of the actions of testosterone
- Negative feedback at the hypothalamus and pituitary,
effects on the brain including libido and effects on the bone
- Aromatose is highly expressed in adipose
tissue - fat men are more feminine
- I love you so much little sex bunny <3 xxxxxx