Reproductive Endocrinology in the Male Flashcards Preview

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Flashcards in Reproductive Endocrinology in the Male Deck (11)
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1

Role of Leydig (interstitial) cells

  • Produce androgens when stimulated by LH
    • 95% of Testosterone
  • T synergizes with FSH to stimulate formation of ABP in Sertoli cells
  • Synthesis of StAR, SCP, SAP
    • Help cholesterol get into cell and make steroids
  • Required for spermiogenesis
  • Have LH receptors (Gs)

2

Role of Sertoli (supporting) cells

  • Form blood-testis barrier via tight junctions
  • Produces androgen binding protein (ABP) 
    • Dramatically increases effectiveness of testosterone
  • Nurture gametes (47 spermatozoa/Sertoli cell)
  • Have FSH receptors (Gs)
    • Produces estrogens from T via aromatase
    • Produces inhibin and other growth factors
  • Support Leydig cells with growth factors + inhibin

3

HPT axis

  • GnRH stimulates production of FSH and LH from pituitary
  • LH acts on Leydig cells
    • Increased testosterone
    • Increased StAR, SCP, and SAP
  • FSH acts on Sertoli cells
    • Increased androgen binding protein (ABP)
    • Increased aromatase
    • Increased growth factors
    • Increased spermatogenesis
    • Increased inhibin

4

Role of HPG axis

  • Males: pulsatile GnRH release leads to pulsatile releases of FSH and LH
  • Females: FSH and LH secretion based on menstrual cycle
  • Androgens inhibit release of GnRH, LH
  • Sertoli cells release:
    • Growth factors to Leydig cells --> increased Leydig cell proliferation --> increased androgen release --> increase Sertoli actions
    • Inhibin which suppresses FSH
  • FSH and LH share an a-subunit with TSH and hCG
    • hCG does jobs of FSH and LH early in embryonic development (< 14 weeks)
    • B subunits of FSH and LH responsible for individual activities of these hormones
    • hCG also responsible for embryonic testosterone formation

5

Forms to which testosterone is converted

  • Testosterone itself
  • Dihydrotestosterone
    • via 5a-reductase
  • Estrogen
    • via aromatase

6

Locations of receptors of testosterone forms

  • Testosterone
    • Androgen receptor
      • Muscles, reproductive organs
  • Dihydrotestosterone
    • Androgen receptor, with higher affinity
      • External genitalia, sebaceous glands, hair follicles
  • Estrogen
    • Estrogen receptor
      • Bone, adipose tissue, brain

7

Functions of testosterone

  • Pubertal development of penis
  • Pubertal development of seminal vesicles
  • Sperm production
  • Causes male voice to deepen
  • Imprint male sex drive, behavior
  • Intrauterine differentiation
  • Contributes to
    • Increased abdominal visceral fat
    • Increased muscle mass
    • Increased RBCs
    • Long bone growth
  • Acts at liver to
    • Increase VLDL
    • Increase LDL
    • Decrease HDL
  • Inhibition of breast growth
  • Negative feedback on gonadotropins, GnRH
  • Stimulation of ABP synthesis in Sertoli cells

8

Functions of DHT

  • Sebaceous gland formation
  • Male pattern hair growth
  • Development of prostate
  • Pubertal development of penis
  • Pubertal development of seminal vesicles
  • Sperm production
  • Feedback on gonadotropins
  • Imprint male sex drive, behavior

9

Functions of estrogen in the male

  • Negative feedback on gonadotropins, GnRH
  • Bone growth
  • Sperm production

10

Changes that take place in male at puberty

  • Increased GH and testosterone
  • Growth spurt usually 11 inches
  • Boys get taller than girls, higher muscle mass, higher skeletal and lean body mass, more muscle cells, less body fat 

11

Roles of GH and sex steroids in bone growth

  • T and E2 stimulate GH secretion and growth
    • Increases IGF-1
    • In absence of androgens, GH causes balanced growth and ossification
  • Testosterone accelerates bone growth, differentiation (maturation), promotes epiphyseal closure, narrows growth window
    • Accomplishes this through estrogen action - aromatase is in bone so T2 --> E2 responsible for these actions
    • High levels of androgens cause accelerated growth, but also accelerated closure and short stature overall