reproduction/sex steroid axis: physiology and biochem

Question 1

what gonadotrophic hormones does the pituitary gland secrete?

Answer 1

• FSH

- LH

Question 2

what hormone produced by the hypothalamus triggers the pituitary to secrete LH/FSH?

Answer 2

GnRH

Question 3

what is the role of FSH in males?

Answer 3

-causes the testes to produce sperm (spermatogenesis)

Question 4

what is the role of FSH in females?

Answer 4

-causes the growth of the ovarian follicles (oogenesis) and it causes the ovary to secrete oestrogen

Question 5

what is the role of LH in males?

Answer 5

-causes the testes to secrete testosterone

Question 6

what is the role of LH in females?

Answer 6

-causes ovulation and it causes progesterone to be produced by the Corpus Luteum

Question 7

what synthesizes and releases GnRH in the hypothalamus?

Answer 7

GnRH neurons within the hypothalamus

Question 8

what is GnRH responsible for?

Answer 8

the release of LH and FSH

Question 9

in what manner is GnRH released?

Answer 9

-a pulsatile manner

Question 10

how is GnRH released in females compared to males?

Answer 10

• in males GnRH is secreted in pulses at a constant frequency
• in females the frequency of the pulses vary during menstrual cycle

Question 11

what do high frequency GnRH pulses stimulate?

Answer 11

-LH

Question 12

what do low frequency GnRH pulses stimulate?

Answer 12

-FSH

Question 13

what effect does estrogen have on GnHR pulses?

Answer 13

-once oestrogen reaches a certain threshold then it will increase the GnRH pulsatility driving the release of LH

Question 14

what effect does progesterone have on GnRH pulses?

Answer 14

-it decreases them

Question 15

what hormones regulate GnRH pulsatility?

Answer 15

-oestrogen and progesterone

Question 16

do GnRH producing neurons contain estrogen and progesterone receptor?

Answer 16

no- the receptors for estrogen and progesterone are found on kisspeptin neurons which then influence GnRH neurons

Question 17

what are the 2 phases of the menstrual cycle?

Answer 17

• follicular phase

- luteal phase

Question 18

how long is the average menstrual cycle?

Answer 18

28 days

Question 19

what day does ovulation occur in the menstrual cycle?

Answer 19

14

Question 20

what occurs in the follicular phase?

Answer 20

-follicular growth

Question 21

what occurs in the luteal phase?

Answer 21

-the corpus luteum is formed under the influence of LH

Question 22

what phase of the menstrual cycle is more variable?

Answer 22

follicular phase

Question 23

describe the affect of hormones on the menstrual cycle?

Answer 23

• FSH stimulates growth of ovarian follicles, increasing oestrogen levels
• rising oestrogen levels exert negative feedback regulation to temporarily lower FSH
• once oestrogen reaches a certain concentration it exerts a positive feedback resulting in an increase in FSH and a surge of LH
• LH surge leads to ovulation and regulates the formation of the corpus luteum and progesterone production/secretion
• increasing progesterone increases the frequency of the GnRH pulses and so decreases LH levels

Question 24

what effect does FSH have on the follicular cells?

Answer 24

-increases the number of follicular cells and accumulation of follicular fluid both resulting in an increase in diameter and overall size of the follicle

Question 25

what effect does oestrogen have on the endometrium?

Answer 25

causes it to thicken

Question 26

what part of the follicle is highlighted blue?

Answer 26

antrum

Question 27

what part of the follicle is highlighted blue?

Answer 27

oocyte

Question 28

what part of the follicle is highlighted blue?

Answer 28

zona pellucida

Question 29

what part of the follicle is highlighted blue?

Answer 29

zona granulosa

Question 30

what part of the follicle is highlighted blue?

Answer 30

theca interna

Question 31

how is oestrogen produced in the follicles?

Answer 31

- LH allows cholesterol to be converted into androgens in the Theca cells - FSH then converts androgen into estrogen in the granulosa cell

Question 32

True or False follicle growth is always controlled by FSH

Answer 32

False In early stages follicles are gonadotrophic independant and so do not require FSH In later stages follicles are gonadotrophic dependant and so require FSH

Question 33

when does ovulation occur after LH surge?

Answer 33

34-36 hours after

Question 34

what hormone stimulates the formation of the corpus luteum?

Answer 34

LH

Question 35

how does LH cause an increase in progesterone production?

Answer 35

-LH stimulates enzymes involved in conversion of cholesterol to progesterone

Question 36

what is the effect of estrogen on vaginal pH?

Answer 36

-reduces vaginal pH through increase in lactic acid production

Question 37

what effect does estrogen have on viscosity of cervical mucus?

Answer 37

-it decreases viscosity of cervical mucus to facilitate sperm penetration

Question 38

what role does progesterone have on pregnancy?

Answer 38

-it maintains pregnancy

Question 39

what effect does progesterone have on the endometrium?

Answer 39

-it maintains the thickness of the endometrium

Question 40

what effect does progesterone have on mucus?

Answer 40

-it is responsible for infertile thick mucus to prevent sperm transport and help prevent infection

Question 41

what effect does progesterone have on myometrium?

Answer 41

-relaxes the myometrium

Question 42

how long does spermatogenic process take place?

Answer 42

70 days

Question 43

what is most of testosterone taken up by?

Answer 43

-Sertoli cells (90%)

Question 44

what role does testosterone play during spermatogenesis?

Answer 44

- maintains the integrity of the blood testes barrier | - releases mature spermatozoa from Sertoli cells by influencing peritubular myoid cells