Sex hormones and oral contraceptives (L18) Flashcards
what is the hypothalamic-pituitary-ovarian axis/tract?
part of the endocrine system
GRH released from the hypothalamus and acts on the anterior pituitary which releases FSH and LH
surge in LH causes ovulation
physiological effects of oestrogen on the endometrium
sensitises LH releasing cells in the pituitary - encourages them to release LH
proliferation of the endometrium
inhibits FSH so regulates cycle
physiological effects of progesterone on the endometrium
renders the endometrium suitable for implanting of a fertilised ovum
maintains endometrium
inhibits further release of GRH, FSH and LH so regulate cycle and ovulation
negative feedback regulation of the hypothalamic-pituitary-ovarian axis
leads to inhibition of GRH, FSH and LH
ensures only 1 egg is released at a time
what are the 2 options after ovulation
fertilisation
no fertilisation
what happens if there is no fertilisation after ovulation?
corpus lute regresses
progesterone levels drop
endometrium cannot be maintained so menstruation occurs
lack of progesterone means clamp on GRH, FSH and LH secretion is released - cycle can start again
follicle development occurs again
what happens if there is fertilisation after ovulation?
fertilised ovum is implanted and secretes human chorionic gonadotrophin (HCG) which stimulates the corpus lute to continue secreting progesterone
maintains endometrium and pregnancy
inhibits further secretion of GRH, LSH, and LH preventing further follicle development
what do GRH, FSH and LH do?
required to induce follicle formation and ovulation
what does oestrogen do?
required to induce proliferation of endometrium
what does progesterone do?
required to maintain pregnancy
required to feedback on hypothalamus and pituitary to inhibit further follicle formation
what are the important targets in regulating ovulation and pregnancy?
GRH, FSH and LH
oestrogen
progesterone
feedback control on hypothalamus and pituitary
GRH, FSH and LH as targets in regulating ovulation and pregnancy
block them with a selective antagonist
inhibits follicle and corpus lute formation and prevents ovulation
however:
• blocking them results in loss of oestrogen and progesterone
• oestrogen required in normal female physiology - without it causes pharmacological menopause
GRH agonists are used to aid fertility
oestrogen as a target in regulating ovulation and pregnancy
oestrogen antagonist useful in preventing proliferation of the endometrium
however, oestrogen required in normal female physiology
oesterogen antagonists used to treat a number of oestrogen dependent cancers
progesterone as a target in regulating ovulation and pregnancy
progesterone antagonists useful in terminating pregnancy
mifepristone, a progesterone antagonist, is used as a morning after pill
feedback onto hypothalamus and pituitary as a target in regulating ovulation and pregnancy
by progesterone
oral contraceptives target the negative feedback system clamping the secretion of GRH, FSH and LH
how do oral contraceptives work?
they trick the hypothalamus into thinking the woman is pregnant
what are the 2 types of oral contraceptives?
combined pill - oestrogen and progesterone
mini pill - progesterone only
the combined pill
oestrogen inhibits secretion of FSH via negative feedback
• this prevents development of new follicle
progesterone inhibits secretion of LH preventing ovulation and makes cervical mucus less suitable for passage of sperm
taken for 21 days then 7 pill free period to have withdrawal bleeding
progesterone only pill
mainly effective due to effect on cervical mucus
doesn’t actually block ovulation
taken continuously
less reliable
side effects of oral contraceptives
- weight gain
- water retention
- mild nausea
- skin changes
- amenorrhoea
what is amenorrhoea?
lack of menstrual period in a woman of reproductive age
more severe side effects of oral contraceptives
vascular
• DVT
• myocardial infarction (heart attack) increased
• stroke increased
GI
• jaundice
mental
• depression
cancer
• may increase or may decrease
why does breast feeding have a contraceptive affect?
baby sucking causes hypothermic nuclei to secrete prolactin releasing factor (PRF) which causes anterior pituitary to release prolactin
regulation of milk production by prolactin
prolactin is the only anterior pituitary hormone than only acts to negatively feedback
inhibits release of GRH and FSH and everything else downstream
breast feeding has a natural contraceptive effect of 6 months
other methods of contraception other than oral contraceptives
male contraception
non-hormonal contraceptives - IUD/coil
condom
