Embryology and Hormones Flashcards
Types of sex
chromosomal, gonadal, phenotypic
Mutations in WT-1 gene (Wilms tumor) associated with
Gonadal dysgenesis, Wilms tumor, nephropathy
Mutations in SF-1 (Steroidogenic factor)
Regulates transcription of genes- deletions cause persistent muellarian system in males
SOX-9
Target of SRY; essential for normal testes development, and elevates AMH concentration with SF-1; deletions of mutations cause skeletal and gonadal dysgenesis
SRY region of short arm of Y chr
Produces testes-determining factor
5th week gestational age
Genital ridges overlay mesonephric ducts
6th week gestational age
primordial germ cells migrate from yolk sac to genital ridges (failure of migration results in streak gonads); primitive sex cords continue to proliferate
7th week gestational age
Gonads are undifferentiated and biopotential;
if male- SRY expression leads to differentiation, Sertoli cells make AMF (leading to Muellarian duct regression), seminiferous tubules and Leydig cells form, medullary cords mature into testis cords;
if female- in absence of y chr and SRY, the gonads develop into ovaries; DAX-1 and WNT-1 cause ovary differentiation, medullary cords degenerate in female
8th week gestational age
Lydia cells start to secrete testosterone
AMH
promotes regression of muellerian structures, produced by stroll cells, if not expressed before 8th week- no muellerian regression
Testosterone
promotes development of internal genetaliea, produced by leydig cells, regression if high levels of testosterone not present
Wolffian ducts become
Seminiferous Tubule
Ejaculatory Duct
Epididymis
Ductus Deferens
Female development
If no testes, then no AMH and no testosterone
Muellerian structures
Fallopian tubes
Midline uterus
Upper 1/3 of vagina
Internal genitalia
Testosterone (produced by leydig cells)
External genitalia
DHT (produced by converting T –> DHT; via alpha reductase)
Sertoli cells
secrete AMH/ MIF; lack of Sertoli cells cause internal male and female genitalia and externally male genitalia
DHT
Formed by enzyme 5 alpha reductase; lack of enzyme causes external female genitalia (until puberty when virilization occurs due increased testosterone levels which cross-react with DHT receptors)
Genital tubercle
penis/clitoris & corpus cavernosum-spongiosum/ vestibular bulbs
Urogenital sinus
Bulbourethral glands/ greater vestibular glands and prostate gland/Skenes’ glands
Urogenital folds
ventral shaft of penis/ labia minora
Labioscrotal swelling
scrotum/ labia majora
46, XX DSD (disorders of sexual differentiation)
Most commonly manifest as CAH; girls typically present with genital ambiguity, but have normal ovaries and uterus
46, XY DSD
Complete gonadal dysgenesis resuts in normal female external genitalia, normal female internal genitalia (b/c of lack of AMH and T), streak gonads
Androgen receptor mutation
X-linked; Causes complete androgen insensitivity syndrome (CAIS)- where people have normal external female genitalia, but male internal genitalia (under developed and undescended)
It presents with increased testosterone, estrogen, and LH
21 hydroxylase deficiency
salt-wasting, hyponatremic, hyperkalemia, decreased cortisol, increased androgens- virilized females
(dx: by measuring 17-hydroxyprogesterone levels)
(tx: hydrocortisone to replace glucocorticoids, and fludrocortisone to replaces mineralocorticoids)
11B- hydroxylase deficiency
salt-retaining, hypertensive, hypokalemic, decreased cortisol, increased androgen (virilization in females)
17 alpha-hydroxylase deficiency
salt-retaining, hypertensive, hypokalemic, decreased cortisol, decreased androgen (undervirilized men)
StAR (cholesterol desmolase) deficiency
Decreased aldo, cortisol, and androgens; increased cholesterol
3B-hydroxysteroid dehydrogenase deficiency
Decreased aldo, cortisol, and androgens; build up of pregnenolones and DHEA (DHEA cross reacts with androgen receptors- so girls are over-virilized, guys are under-virilized because of decreased T production)
Blood-testes barrier
tight junctions between Sertoli cells
Testosterone
Local (maintains wolffian ducts and internal male sex organs)
Systemic (converted to DHT with results in development of external genitalia)
Leydig cells- functions
- Synthesize testosterone (by stimulation of LH (acts via Gs))
- Testosterone + FSH stimulate ABP production in Sertoli cells
- Synthesize StAR, SCP (sterol carrier protein and steroid activating protein)- (helps cholesterol get into the cell and make steroids)
- Spermiogenesis
Sertoli cells- functions
- Forms blood-testis barrier via tight junctions
- Produces ABPs (increases testosterone effects)
- Nurture gametes
- FSH receptors (Gs)- produce estrogen via aromatase AND inhibin (inhibits FSH)
- Supports Leydig cells with growth factors and inhibin
StAR protein
Rate limiting step of cholesterol transport
Desmolase
Rate limiting enzyme in testosterone synthesis
LH vs. FSH receptors
LH receptors: Leydig/ Theca
FSH receptors: Sertoli/ Granulosa
Feedback mechanisms: Sertoli cells
Sertoli cells: Respond to FSH –> growth factors to Leydig cells –> increase Leydig proliferation –> increase androgen release –> increase Sertoli actions
Also secretes inhibin –> supresses FSH release
Pulsatile vs. Continuous signal
Pulsatile: pulsatile release of FSH and LH
Continuous: inhibition of FSH and LH
Feedback mechanisms: Leydig cells
Leydig cells: Respond to LH –> Secrete testosterone –> Testosterone –> inhibit release of GnRH and LH
Shared subunits
FSH and LH share alpha subunit with TSH and hCG
hCG does job of FSH and LH early in embryonic development
hCG can cross-react with LH receptor and stimulate Leydig cells to produce testosterone
Testosterone function
- Development of internal male genitalia (Seminiferous Tubules, Epididymis, Ejaculatory duct, Ductus deferens)
- Sperm production
- Growth of external genitalia during puberty (penile growth and development of seminal vesicles)
- Increases male sex drive, behavior, deepening of voice
- Inhibits breast growth
- Stimulates ABP synthesis in Sertoli cells
- Acts on liver to: increase VLDL, increase LDL and decrease HDL
- Feedback on gonadotropin (-)
Dihydrotestosterone (DHT) function
Converted from testosterone via 5 alpha reductase
DHT potency»_space; testosterone
- Sebaceous gland formation
- Male pattern hair growth
- Development of prostate
- Pubertal development of penis and seminal vesicles
- Sperm production
- Male sex drive, behavior
- Feedback on gonadotropins (-)
Estrogen (estradiol) function:
Synthesized from testosterone via aromatase
- Feedback on gonadotropins (-)
- Bone growth (fusion of epiphyseal plates)
- Sperm production
Male puberty changes
- Increase in GH and testosterone
- Growth spurt (usually 11 in)
- Order of events: Adrenarche –> Gonadotropins increase –> Testicular size increases –> Testosterone increases –> Pubic hair development –> Penile growth –> Sperm production –> Growth spurt
Growth hormone effects on bone growth
Testosterone and Estrogen stimulate GH secretion (which increases IGF-1)
In the absence of E and T, GH causes balanced growth and ossification
Testosterone/ Estrogen effects on bone growth
Accelerates bone growth, differentiation (maturation), epiphyseal closure, narrows growth window
High androgen levels can cause accelerated growth, but also accelerated closure and short stature
