Gonads 2

Question 1

Name the weak androgen that is produced both in the adrenal glands and in the testes.

Answer 1

Androstenedione

Question 2

What two reactions can testosterone follow and what do they produce?

Answer 2

Testosterone —> Oestrogen (aromatisation - by the action of aromatase)
Testosterone —> Dihydrotestosterone (reduction)
Dihydrotestosterone is a more potent androgen that binds to the same androgen receptors as testosterone.

Question 3

How is testosterone and DHT transported in the blood?

Answer 3

Mainly bound to sex hormone binding globulin (SHBG)
Some of it is bound to albumin
A small amount is free and bioactive
This is in dynamic equilibrium

Question 4

How is testosterone and DHT transported in the seminiferous tubules?

Answer 4

Bound to androgen binding globulin (ABG)

Question 5

What are the effects of androgens in the foetus and in adults?

Answer 5

Development of male internal and external genitalia
Stimulates general growth
Adult - spermatogenesis, pubertal growth spurt, stimulates protein synthesis

Question 6

Define oestrogen.

Answer 6

Any molecule that induces mitosis in the endometrium.

Question 7

What is the main oestrogen in the menstrual cycle?

Answer 7

17 beta oestradiol

Question 8

What is the main oestrogen in pregnancy?

Answer 8

Oestriol

Question 9

What are the actions of oestrogens?

Answer 9

Stimulate mitosis in the endometrium 
Increased salt and water reabsorption
Increase HDL
Causes LH surge
Stimulates growth of ductile system in the breast 
Decreases sebaceous gland secretion

Question 10

Define progestogen.

Answer 10

Any molecule that induces secretory changes in the endometrium

Question 11

What are the actions of progestogens?

Answer 11

Stimulates secretory activity in the endometrium and cervix
Decrease renal NaCl absorption
Growth of alveolar system in breast
Increase in body temperature

Question 12

What hypothalamic hormone stimulates FSH and LH release from the pituitary gland?

Answer 12

Gonadotrophin Releasing Hormone (GnRH)

Question 13

Which cells in the testes have receptors for FSH and LH?

Answer 13

Sertoli Cells - FSH

Leydig Cells - LH

Question 14

Describe the negative feedback from the testes to hypothalamo-pituitary axis.

Answer 14

Sertoli Cells - produce INHIBIN - negative feedback effect on hypothalamus and pituitary
Leydig Cells - produce TESTOSTERONE - negative feedback effect on hypothalamus and pituitary

Question 15

How do these pathways cause negative feedback?

Answer 15

Decreases the AMPLITUDE of the GnRH pulses.

Question 16

Describe the local positive feedback loop in the ovaries.

Answer 16

FSH stimulate aromatase and increase conversion of androgens to 17 beta oestradiol.
Oestrogen then leaves the granulosa cell and binds to oestrogen receptors on the SAME granulosa cell and further stimulates production of oestrogen.

Question 17

Rising oestrogen levels has a negative feedback effect on FSH.

Answer 17

Most developing follicles will then undergo atresia and only one follicle remains, the Graffian follicle. What enables this follicle to survive the negative feedback on FSH?
The Graffian follicle is no longer FSH-dependent and can survive with it’s own local production of oestrogen.
The other cells are FSH-dependent and so undergo atresia when the FSH is removed.

Question 18

What conditions must be in place for the rising oestrogen concentration switch from negative feedback to positive feedback on gonadotrophins?

Answer 18

Absence of progesterone

Oestrogen concentration must be high enough for a minimum of 36 hours

Question 19

The oestrogen levels in the luteal phase are as high as the levels that triggered ovulation in the follicular phase so why is there no LH surge in the luteal phase?

Answer 19

Presence of progesterone

Question 20

If fertilisation occurs, high levels of oestrogen and progesterone is needed. What molecule is produced to mimic LH and stimulate further oestrogen and progesterone production?

Answer 20

Human Chorionic Gonadotrophin

Question 21

If fertilisation does not occur, what happens?

Answer 21

Oestradiol, Progesterone and Inhibin have negative feedback effect on FSH and LH leading to luteolysis and menstruation.

Question 22

What is the difference between primary and secondary amenorrhoea?

Answer 22

Primary - never had a period

Secondary - used to have period but then they stopped

Question 23

Define infertility.

Answer 23

Woman - inability to get pregnant

Man - inability to impregnate