HPG Axis Flashcards
Describe release of gonadotropin releasing hormone from the hypothalamus before and after puberty
Before- continuous
After - PULSATILE (continuous would result in down-regulation of pituitary receptors)
What does chorionic (hCG) gonadotopin bind
the same receptor as lutenizing hormone (LHCGR)
Sex steroids (hormones) are all derived from what
cholesterol
The 3 families of sex steroids (hormones) are
oestrogens - femalesness
androgens - malesness
progestagens - pregnancy
Components of the HPG axis in women
Hypothalamus > ant pituitary (GnRH)
Ant. pituitary > ovaries (FSH, LH)
Ovaries (oestrogen, progesterone)
+ve/-ve feedback
Components of the HPG axis in men
Hypothalamus > ant pituitary (GnRH)
Ant. pituitary > testis (FSH, LH)
Testis (inhibin, testosterone)
-ve feedback
How long is the menstrual cycle
26-32 days
28 average
Which phase of the ovarian cycle is constant and which phase varies in length between women?
follicular phase varies
luteal phase is 14 days (post-ovulation)
Which day of the menstrual cycle do we measure FSH/LH on
FSH/LH by convention measured on day 2 or 3 so we’re comparing against the same levels
Primary amenorrhea
never had a period
Secondary amenorrhea
had periods previously, but not had one in 6 months
what does FSH do
stimulates development of primary follicles (5-15 per month)
what does LH do
stimulates follicle maturation in preparation for ovulation, ovulation (and all the changes needed for it), and development of the corpus luteum
what does LH do
stimulates follicle maturation in preparation for ovulation, ovulation, and development of the corpus luteum
what does oestrogen do
moderate level have negative feedback onto HPG axis causing FSH level to fall and a dominant follicle to be selected
high level has positive feedback onto HPG axis causing the LH surge (and FSH rise) which triggers ovulation
it also thickens endometrium and thins cervical mucus
what does progesterone do
gives negative feedback onto the HPG axis so LH/FSH secretion is reduced, in pregnancy this halts the cycle and prevents ovulation
Maintains the endometrium in the secretory phase ready to receive an embryo
