Reproductive endocrinology Flashcards
Gonadotropin-releasing hormone (GnRH)
produced in hypothalamus in pulses
stimulates secretion of luteinizing hormone (LH) and follicle stimulating hormone (FSH) by the anterior pituitary
Luteinizing hormone (LH)
Males:promotes synthesis of testosterone by Leydig cells of the testes
negative feedback of testosterone on hypothalamus and pituitary
Females: ovulation
Follicle stimulating hormone (FSH)
stimulates spermatogenesis by Sertoli cells of the testis
sertoli cells produce inhibin –> negative feedback on anterior pituitary
females: act on ovaries, negative feedback through estrogen and progesterone
Testosterone
circulates bound to protein Sex Hormone Binding Globulin (SHBG)
Converted in target tissues to dihydrotestosterone (DHT) by 5a-reductase
DHT
a more potent androgen than testosterone
Androgen resistance
rare genetic disorder due to lack of testosterone receptor or deficiency of 5a-reductase
result: high testosterone level, low DHT
Primary Hypogonadism (m)
testes dysfunction
low serum testosterone, high LH/FSH
causes: Kleinfelters, mumps, varicocele (damaged/blocked testicular vein)
Secondary hypogonadism (m)
pituitary dysfunction
result: low serum LH and FSH, low testosterone
causes: pituitary damage, tumors in pituitary, loss of pulsatility of GnRH
Tertiary hypogonadism (m)
hypothalamus dysfunction
causes: Kalmann- lack of migration of GnRH neurons to hypothalamus during embryonic development
GnRH stimulation test
used to differentiate between secondary and tertiary causes of hypogonadism
secondary: pituitary wont respond properly
tertiary: can respond
Gynecomastia
breast enlargement in men due to estrogen androgen imbalance
common in alcoholic liver disease and general obesity
Androgens from adrenal cortex
androstenedione and DHEA (DHEA-S) in both males and females
Estrogen
sex hormone from the ovaries
secreted mainly as estradiol
most estradiol is bound to SHBG
Progesterone
sex hormone from the ovaries
most progesterone in serum is bound to albumin
3 phases of the 28-day ovulation cycle of the human female
Follicular phase
Ovulatory phase
Luteal phase
Follicular phase
FSH and LH levels start to increase –> estradiol production and follicular development
Ovulatory phase
estradiol threshold is met –> stimulate increase in LH levels through positive feedback –> ovulation
Luteal phase
corpus luteum produces estradiol and progesterone to thicken the uterine lining (endometrium)
day 22: corpus lutem regresses –> fall in estradiol/progesterone –> menstruation
Day one is marked by
first day of menstruation
If pregnancy occurs
estradiol and progesterone do not fall and continue as per positive feedback
Primary hypogonadism (f)
dysfunction of ovaries
result: low serum estradiol, high LH FSH
causes: Turner’s, premature menopause, polycystic ovarian syndrome
Secondary hypogonadism (f)
dysfunctoin at pituitary
result: low serum LH FSH, low estradiol
causes: pituitary damage, tumors
Tertiary hypogonadism (f)
dysfunction at hypothalamus
causes: Kalmann
Hirsutism and virilization
overproduction of androgens –> male pattern of body hair (hirsutism)
masculinization of females from elevated level of androgens (v)
