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53016
Male Reproductive Hormones
Description
Endocrinology Mind Map on Male Reproductive Hormones, created by maisie_oj on 22/04/2013.
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endocrinology
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Resource summary
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
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