Session 2 - Control of reproductive processes

Question 1

What are the glycoprotein hormones that the ant pit secretes? What cell type produces each hormone?

Answer 1

FSH – produced by gonadotrophs
LH - produced by gonadotrophs
TSH - produced by thyrotrophs

Question 2

What are the polypeptide hormones that the ant pit secretes? What cell type produces each hormone?

Answer 2

GH - produced by somatotrophs
ACTH - produced by Corticotrophs
Prolactin - produced by lactotrophs

Question 3

What are the hormones that the post pit produces?

Answer 3

ADH
Oxytocin (important for reproduction)

Question 4

How is gonadotrophin secretion controlled by the hypothalamus? What is the releasing hormone of FSH and LH?

Answer 4

• Anterior pituitary secretion controlled by hypothalamus via releasing hormones
• These travel in hypophyseal portal circulation
• Releasing hormones released by neurosecretory neurons.
• Arterial blood arrives in hypothalamus, picks up releasing hormones and moves onto into hypophyseal portal circulation to the anterior pituitary (therefore don’t need to secrete much hormone as it doesn’t get diluted due to direct blood supply).
• Releasing hormone is GnRH

Question 5

what is the nature of FSH and LH release?

Answer 5

puslatile - once an hour

Question 6

What are the actions of FSH and LH?

Answer 6

steroidogenesis, gonadal growth, gametogenesis

Question 7

What influences GnRH secretion?

Answer 7

• Feedback from gonads - inhibited by steroids
• Environmental effects, body weight

Question 8

What is the action of GnRH in males? What is the action of FSH and LH? What is inhibin secretion rate related to? What else can affect the production of testosterone?

Answer 8

• Testosterone reduced GnRH secretion
• Spermatogenesis occurs continuously and male must be ready for action at any time. Therefore, hormone levels constant in medium and long term, achieved by –ve feedback
• FSH binds to Sertoli cells
• LH binds to Leydig cells:
  
  • Promotes testosterone release and spermatogenesis
• Inhibin secretion related to rate of spermatogenesis.
• Testosterone is higher in mornings due to circadian rhythms and can be affected by environmental stimuli

Question 9

What happens to GnRH under:

a) moderate amounts of oestrogen secretion
b) high amounts of oestrogen alone?
c) progesterone?

Answer 9

a) Moderate amounts – reduce GnRH secretion, reduces amount of GnRH per pulse
b) High amounts ALONE – Promote GnRH secretion, promotes LH surge

c) Prevents positive feedback of high oestrogen
Increases inhibitory effects of moderate oestrogen
Reduces frequency of GnRH pulses

Question 10

What does inhibin do in both sexes? What is inhibin secretion related to?

Answer 10

Inhibin from gonad reduces FSH secretion
Inhibin secretion related to developing gametes - More developed gametes release more inhibin

Question 11

What are the 3 phases of the menstrual cycle?

Answer 11

Follicular, ovulation, luteal

Question 12

What is the action of FSH and Lhg in the follicular phase? What does oestrogen stimulate during this phase?

Answer 12

FSH binds to granulosa cells
LH binds to thecal cells (of theca interna)
Stimulates development of follicle

Oestrogen in this phase stimulates:

Fallopian tube function
Thickening of endometrium
Growth and motility of myometrium
Thin alkaline cervical mucus
Vaginal changes
Calcium metabolism

Question 13

What is the action of LH pre-ovulation?

Answer 13

• LH surge stimulates ovulation.
• LH surge weakens theca externa and allow ovum to burst through

Question 14

What is the action of LH during the luteal phase? What about progesterone? How do progesterone only contraceptives function?

Answer 14

LH maintains corpus luteum

Progesterone in this stage acts on oestrogen primed cells:

Further thickening of endometrium
Thickening of myometrium
Thick, acid cervical mucus – barrier against sperm and bacteria between uterus and vagina. This is how progesterone only contraceptives work.

Changes in mammary tissue

Question 15

At the beginning of the menstrual cycle, what are the levels of progesterone and oestrogen? What happens here?

Answer 15

Low progesterone and oestrogen

FSH levels rise:

• Binds to granulosa cells
• Theca interna develops
• Secretes oestrogen stimulated by LH
• Secretes inhibin

Question 16

What happens in the mid follicular stage?

Answer 16

• Oestrogen levels rising
• Inhibin levels rising – inhibit FSH, no new follicles can develop
• Oestrogen exerts +ve feedback at hypothalamus and pituitary
• LH levels rise but not FSH

Question 17

What happens in the pre-ovulatory phase?

Answer 17

LH surge. Precise timing may be influenced by environmental factors

Question 18

What happens after ovulation?

Answer 18

Corpus luteum spontaneously forms:

• Begins to secrete progesterone and oestrogen
• Maintains suppression of FSH
• LH also suppressed because +ve feedback inhibited by progesterone

Question 19

How long does the luteal phase last? What happens during it?

Answer 19

• Corpus luteum grows and secretes more steroids
• After 14 days it dies

Question 20

What happens if there is no pregnancy after the luteal phase?

Answer 20

• Death of corpus luteum
• Rapid fall in steroid levels
• Stimulates menstruation
• Relieves inhibition of FSH

Question 21

What happens after the luteal phase if there is a preganancy?

Answer 21

If pregnancy occurs, HCG released by placenta preserves corpus luteum. Corpus luteum secretes increasing amounts of steroids but placenta soon secretes even more and after 12 weeks corpus luteum no longer supports pregnancy.

Question 22

Why does the menstrual cycle vary in length? How many days is it from ovulation to menses?

Answer 22

Variation in timing of ovulation. From ovulation to menses always takes 14 days

Question 23

What happens to hormone levels after menopause and why?

Answer 23

Ovary secretes less oestrogen so levels of FSH, LH and GnRH rise.

FSH increases more than LH because there is no inhibin secreted from ovary.

Question 24

How does prolactin suppress fertility?

Answer 24

Supresses FSH and GnRH