HPG Axis Flashcards
What does HPG stand for?
Hypothalamic pituitary gonadal
What hormones released from the hypothalamus act on the anterior pituitary?
CRH TRH GHRH Somatostatin GnRH PRH Dopamine
Which hormones are released from the anterior pituitary?
FSH LH ACTH TSH GH Prolactin
What is the action of somatostatin?
Inhibits GH release
What is the action of dopamine?
Inhibits prolactin secretion
What are the alternative names for the anterior pituitary?
Pars distalis
Adrenohypophysis
What are the alternative names for the posterior pituitary?
Pars nervosa
Neurohypophysis
What connects the anterior pituitary to the hypothalamus?
Superior hypophyseal artery
What type of molecule is GnRH?
Peptide
10 amino acids in length - small
How often is GnRH released?
Every 1 - 3 hours, pulsatile
GnRH stimulates the release of …
FSH and LH
Which cells in the AP release FSH and LH?
Gonadotrophs
In the male, which cells do FSH and LH act on?
FSH - Sertoli cells
LH - Leydig cells
What happens when Sertoli cells are stimulated?
Spermatogenesis occurs (testosterone from Leydig cells needed) Inhibin released - negative feedback on hypothalamus and AP
What happens when Leydig cells are stimulated?
Testosterone released
Some kept locally to help with spermatogenesis
Negative feedback on AP and hypothalamus
What is the role of inhibin?
Inhibin released when spermatogenesis increases
Selectively inhibits FSH release to reduce spermatogenesis
What is the role of androgen binding hormone?
Binds some testosterone to keep within the tubules
When are testosterone levels the highest?
Early morning
In the female, which cells do FSH and LH act upon?
Theca cells - LH
Granulosa cells - FSH and LH
Moderate amounts of oestrogen have what effect?
Negative feedback on AP and hypothalamus
What happens when we have high concs of oestrogen in the absence of progesterone?
Positive feedback
Increased GnRH secretion
LH surge (for ovulation)
Describe the hormone levels during menses
Moderate oestrogen
LH and FSH kept low
How do oestrogen and progesterone differ in decreased GnRH?
Oestrogen reduce amount per pulse
Progesterone decreases frequency of pulses
