Reproductive hormones ans HPG axis

Question 1

What reproductive hormones are produced by the hypothalamus?

Answer 1

GnRH (gonadotropin releasing hormone)

Question 2

What repro hormones are produced by the pituitary gland?

Answer 2

Anterior - Gonadotropins (FSH and LH), prolactin
Posterior - oxytocin

Question 3

What repro hormones are produced from the gonads?

Answer 3

Ovary - oestrogens, progesterone, inhibin, oxytocin, relaxin and some testosterone
Testis - testosterone and other androgens, oestrogen, inhibin

Question 4

What repro hormones are produced from the uterus/placenta?

Answer 4

prostaglandin F2a, progesterone, oestrogen, eCG (equine chorionic gonadotropin)

Question 5

What is the steroid synthesis pathway?

Answer 5

Cholesterol
Pregnenolone
Progesterone
Testosterone
Oestradiol

Question 6

Describe the process of steroid metabolism

Answer 6

Question 7

What are prostaglandins synthesised from?

Answer 7

arachidonic acid

Question 8

What are the function of prostaglandins in reproduction?

Answer 8

PGF2a and PGE2
important in ovulation
parturition
luteolysis

Question 9

Label the vascular connection between the hypothalamus and the pituitary (hypothalamo-hypophyseal-portal system)

Answer 9

Question 10

Describe the function of the hypothalamo-hypophyseal-portal system

Answer 10

Question 11

Describe the HPT axis

Answer 11

The male hypothalamus releases frequent intermittent bursts of GnRH that occur day and night
Pulse of GnRH -> pulse of LH -> pulse of testosterone

Question 12

Describe the control of hormone production in the testes

Answer 12

Leydig cells - LH receptor +ve -> testosterone production
Sertoli cells - FSH receptor +ve - inhibin production (inhibits FSH and LH- negative feedback loop)

Question 13

Label the HPT axis

Answer 13

Question 14

What are the major structures of the ovary?

Answer 14

Follicles
Corpus luteum

Question 15

What is the role of the follicle in the ovary?

Answer 15

oocyte (egg) develops inside
oestradiol secretion - receptivity and conception

Question 16

What is the function of the corpus luteum

Answer 16

Transient endocrine gland
progesterone secretion - pregnancy support

Question 17

Describe the hormonal onset of ovulation

Answer 17

Basal secretion of GnRH until stimulated by increased oestrogen
Large preovulatory surge of GnRH -> ovulation

Question 18

Describe the hypothalamic-pituitary-ovarian axis

Answer 18

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

Question 19

What is the function of luteolysis

Answer 19

In the absence of fertilisation the CL undergoes structural and functional regression leading to decreased progesterone secretion which removes the -ve feedback of GnRH