Reproductive hormones ans HPG axis Flashcards
What reproductive hormones are produced by the hypothalamus?
GnRH (gonadotropin releasing hormone)
What repro hormones are produced by the pituitary gland?
Anterior - Gonadotropins (FSH and LH), prolactin
Posterior - oxytocin
What repro hormones are produced from the gonads?
Ovary - oestrogens, progesterone, inhibin, oxytocin, relaxin and some testosterone
Testis - testosterone and other androgens, oestrogen, inhibin
What repro hormones are produced from the uterus/placenta?
prostaglandin F2a, progesterone, oestrogen, eCG (equine chorionic gonadotropin)
What is the steroid synthesis pathway?
Cholesterol
Pregnenolone
Progesterone
Testosterone
Oestradiol
Describe the process of steroid metabolism
What are prostaglandins synthesised from?
arachidonic acid
What are the function of prostaglandins in reproduction?
PGF2a and PGE2
important in ovulation
parturition
luteolysis
Label the vascular connection between the hypothalamus and the pituitary (hypothalamo-hypophyseal-portal system)
Describe the function of the hypothalamo-hypophyseal-portal system
Describe the HPT axis
The male hypothalamus releases frequent intermittent bursts of GnRH that occur day and night
Pulse of GnRH -> pulse of LH -> pulse of testosterone
Describe the control of hormone production in the testes
Leydig cells - LH receptor +ve -> testosterone production
Sertoli cells - FSH receptor +ve - inhibin production (inhibits FSH and LH- negative feedback loop)
Label the HPT axis
What are the major structures of the ovary?
Follicles
Corpus luteum
What is the role of the follicle in the ovary?
oocyte (egg) develops inside
oestradiol secretion - receptivity and conception
What is the function of the corpus luteum
Transient endocrine gland
progesterone secretion - pregnancy support
Describe the hormonal onset of ovulation
Basal secretion of GnRH until stimulated by increased oestrogen
Large preovulatory surge of GnRH -> ovulation
Describe the hypothalamic-pituitary-ovarian axis
Follicular phase:
- for most of this phase low eostradiol (E2) has a negative feedback role
- approaching ovulation there is a critical switch and rising E2 become +ve leading to an LH surge and ovulation
- inhibin specifically inhibits FSH
Luteal phase:
- Corpus luteum produces progesterone which has a negative effect on GnRH neurones to prevent oestrus
What is the function of luteolysis
In the absence of fertilisation the CL undergoes structural and functional regression leading to decreased progesterone secretion which removes the -ve feedback of GnRH
