11 puberty, secondary sexual characteristics, menstrual cycle, contraception

Question 1

what are the 6 major hormones, where are they released from?

what type of hormones are they on a molecular level?

Answer 1

• Gonadotrophin releasing hormone (GnRH)- hypothalamus, decapeptide
• FSH- ant pituitary . two glycosylated proteins
• LH- ant pituitary. two glycoslated proteins
• oestradiol- ovary. steroid
• progesterone-ovary. steroid
• testosterone- testis, adrenal gland, ovary. androgen

Question 2

oestrogens=?

Answer 2

oestradiol+ oesterone

Question 3

how does GnRH travel to the anterior pituitary?

Answer 3

via hypothalamo-pituitary portal vessels

Question 4

days 0-14 of menstrual cycle in terms of GnRH, FSH, LH, oestradiol

Answer 4

• surge in GnRH stimulates secretion of FSH and LH-> act on ovary
• FSH act on follicle causing oestradiol to be produced on granulosa cells -> -ve feedback on ant. pituitary (LH also stimulates oestradiol)
• -ve feedback causes drop in LH and FSH in first half of cycle

Question 5

effects of LH and FSH days 0-14

Answer 5

FSH: acts on granulosa cells on follicle to increase synsthesis of oestradiol

LH: act on thecal cells on follicles to produce androgens

Question 6

what is cholesterol used to produce

Answer 6

• androgens
• oestrogens (from androgen)
• glucocorticoids and mineralocorticoids in adrenal cortex

Question 7

what can be used to treat breast cancer

Answer 7

block conversion of testosterone to oestrogens

Question 8

what cells do LH bind to in the synthesis of oestradiol?

what reaction does this cause?

Answer 8

• LH binds to receptors on thecal cells
  
  • cholesterol-> androstendione

Question 9

why must androstendione be produced on thecal cells and not on granulosa cells?

Answer 9

granulosa cells do not have enzymes to produce androstendione

Question 10

what type of activity allows the formation of oestradiol from andostenedione?

Answer 10

aromatase activity when FSH binds to receptors on gransulosa cells

Question 11

which receptors do thecal and granulosa cells contain?

Answer 11

thecal cells only have receptors for LH

granulosa cells have FSH and then switch to LH

Question 12

day 0-14: why do oestradiol levels rise when FSH and LH levels drop?

Answer 12

oestradiol increases proliferation of granulosa cells -> more oestradiol produced -> bind to receptors on granulosa cells

positive feedback

Question 13

ovulation: what do high oestradiol levels cause in late follicular stage? at mid cycle

Answer 13

act on pituitary to release more LH (via GnRH)

at mid cycle -ve feedback becomes positive to allow a short surge of LH

Question 14

what happens to granulosa cells at mid cycle?

Answer 14

• high oestradiol and FSH causes change of action of LH
• stimulate LH receptors on granulosa cells
• increasing progesterone synthesis

Question 15

what is the dominant hormone in the second half of cycle?

how does this come about?

Answer 15

progesterone

presence of high LH and cholesterol converted to progesterone on granulosa cells

Question 16

corpus luteum - what is it formed by?

how is maintained?

what does it secrete?

how many days is the life of CL if not pregnant?

Answer 16

• formed by collapsed follicle
• maintained by LH
• secrete progesterone (maintain endometrium)
• oestradiol levels begin to drop (progesterone inhibits oestradiol synthesis)
• low levels of LH maintain CL. life of CL in non pregnant is 14 days

Question 17

what happens to hormones in days 14-28?

GnRH

FSH and LH

Answer 17

• progesterone causes a decrease in gonadatrophin secretion (suppress GnRH secretion- decrease in oestradiol levels also decrease GnRH)
• FSH and LH levels are low so no new follicles develop

Question 18

death of corpus luteum

Answer 18

• Corpus luteum degenerates (due to production of PGF2a)
• Decrease in progesterone and oestradiol levels
• Increase in FSH and LH levels allow new follicles to mature
• Onset of menstruation

Question 19

Answer 19

Question 20

how does hormonal contraception suppress ovulation?

Answer 20

• Suppress ovulation by negative feedback of progesterone on the pituitary and hypothalamus
• Decrease in GnRH secretion resulting in low FSH and LH levels – no new follicles develop

Question 21

cessation of menstrual cycle in pregnancy

Answer 21

• No menstrual cycle occurs as high levels of progesterone are present.
• Inhibit secretion of pituitary gonadotrophins
• CG secreted by trophoblast cells.

Question 22

what do low concentrations of oestradiol cause on LH before 10 days of menstrual cycle? how does this differ after 10 days?

Answer 22

negative feedback on LH at low conc

positive feedback on LH at high conc after 10 days

Question 23

what happens at ovulation?

Answer 23

oocyte release

recruitment of 5-9 new follicles