L14 oestrogen and others

Question 1

Regulation of the Hypothalamic-Pituitary-Ovarian axis

Answer 1

Regulation of the hypothalamic-pituitary unit is a complex process involving both negative and positive feedback mechanisms in the female

Question 2

The axis diagram

Answer 2

On slides

Question 3

Axis diagram poor but +feedback to ovulation

Answer 3

Hypothemus
↓GnRH
Anterior pituitary
↓FSH/LH
Estrogen←Ovary→Progesterone

Estro -> anterior
Pro -> Anterior and hypo as negative

Question 4

Natural estrogens

Answer 4

• 17b-Estradiol is an 18-carbon steroid hormone synthesized mainly by maturing follicle in 1st half of cycle
• Ligation and dimerisation of E receptors in nuclues and activates ER-gene expression
  *

Question 5

Natural progestogens

Answer 5

• Progesterone, is a 21-carbon steroid secreted mainly by the corpus luteum in 2nd half of cycle
• Activation of receptors, dimerisation, nuclear translocation
• Gene expression

Question 6

Actions of E2 in menstral cycle

Answer 6

• modulates FSH & LH release
• stimulates endometrial proliferation and growth; breast growth
• increases expression of progesterone receptors
• stimulates copious, watery secretions from cervix

Question 7

Actions of P4 in the menstrual cycle

Answer 7

• modulates FSH & LH release
• stimulates cyclical growth of uterus and breasts
• reduces uterine excitability
• produces secretion of less abundant, thicker mucus from cervix (sperm hostile)
• reduces proliferative effect of E2 in endometrium in late luteal phase (inhibits implantation)

Question 8

E2 and P4 in fertility, conception and pregnancy

Answer 8

• E2 and P4 stimulate growth of the endometrium in preparation for implantation
• If no conception after ovulation, P4 induces changes in cervical mucous that prevents sperm motility; levels decline as corpus luteum regresses and –ve feedback wanes
• If conception and implantation occur, elevated levels of P4 (and E2) are maintained by developing placenta and pituitary FSH/LH suppression continues
• P4 required for embryo survival and to prevent immune rejection (P4 used to prevent recurrent early pregnancy loss)
• Elevated P4 levels need to be maintained throughout pregnancy (via placental production) to maintain embryo viability and uterine quiescence. Levels drop after delivery.
• E2 is less important for maintaining pregnancy, although is important in labour and delivery

Question 9

Oral contraceptive mimic the ≈____ environement of prenancy shutting down the ovulatory cycle and preventing ovulation and ____ and implantation

Answer 9

Endocrine
fertilisation