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 Dihydrotestosterone 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 Dihydrotestosterone 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
some androgenic effects are mediated by conversion to oestrogen.

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 which is why women are more protected from cardiovascular problems than men before reaching menopause
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 (they are thick and viscous so are less easily penetrated by spermatozoa than oestrogen induced watery secretions) 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 and how is it released?

Answer 12

Gonadotrophin Releasing Hormone (GnRH)

it is released in pulses.

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 - have LH receptors and LH stimulates production of TESTOSTERONE (has virilisation effects, development of male physical characteristics) - 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 and where does this happen.

Answer 16

happens in the graffian cells, causes the nearby granulosa cells to grow more and produce more oestrogen.
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

what happens to the other follicles that are not graafian and why/

Answer 17

Most developing follicles will then undergo atresia and only one follicle remains, the Graffian follicle/dominant follicle (this one produces more oestrogen). 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.
The rising oestrogen has a negative feedback on FSH.

Question 18

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

Answer 18

Absence of progesterone Oestrogen concentration must be high enough for a minimum of 36 hours, this positive feedback causes the LH surge

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

Question 24

what are some causes of infertility?

Answer 24

Pituitary failure
Prolactinoma- inhibits LH and FSH (prolactin is released during pregnancy for evolutionary reasons so you don’t get pregnant again)
Testicular failure e.g. mumps, klinefelter syndrome
ovarian failure

Question 25

what is the difference between amenorrhoea and oligomonerrhoea?

Answer 25

Amenorrhoea: absence of menstrual cycles.
Oligomenorrhoea: infrequent menstrual cycle, could be due to absence of LH surge due to insufficient oestrogenic effect at the end of the follicular phase.

Question 26

how do thecal and granulosa cells work?

Answer 26

Thecal cell= LH receptor
Granulosa cell= FSH receptor

thecal cells respond to LH by increasing androgen production and FSH binds to FSH receptor on granulosa cells which activates aromatase which converts androgen to 17b-oestrodiol.

Question 27

describe what happens during ovulation

Answer 27

The LH surge causes the egg to pop.