Endo 10 - Gonads 2

Question 1

What is the weak androgen produced by both the adrenals and the gonads?

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) (in the liver, skin, brain, adrenals)
Testosterone —> Dihydrotestosterone (reduction) (in the prostate, testes, skin, brain)
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) 60%
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, secondary sex glands, secondary sex characteristics, stimulates protein synthesis, behavioural effect

Question 6

Define oestrogen.

Answer 6

Any molecule that induces mitosis in the endometrium.
Examples
17beta-oestradiol (main)
oestrone (precursor)

Question 7

What is the main oestrogen in the menstrual cycle?

Answer 7

17 beta oestradiol

Question 8

What are the actions of oestrogens?

Answer 8

Stimulate mitosis in the endometrium
Maturation of follicle
Causes LH surge
Stimulates growth of ductile system in the breast

Increased salt and water reabsorption
Increase HDL
Decreases sebaceous gland secretion
stimulate osteoblasts

Question 9

Define progestogen.

Answer 9

Any molecule that induces secretory changes in the endometrium

Question 10

What are the actions of progestogens?

Answer 10

Stimulates secretory activity in the endometrium and cervix
Stimulates growth of alveolar system in the breast
Decrease renal NaCl absorption (competitive inhibition of aldosterone)
Increase in body temperature

Question 11

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

Answer 11

Sertoli Cells - FSH - secrete inhibin

Leydig Cells - LH - secrete testosterone

Question 12

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

Answer 12

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

Question 13

How do these pathways cause negative feedback?

Answer 13

Decreases the AMPLITUDE of the GnRH pulses.

Question 14

Spermatogenesis requires what to be complete?

Answer 14

Both testosterone and sertoli cells so the LH/testosterone system and the GnRH/FSH system

Question 15

Spermatogenesis requires what to be complete?

Answer 15

Both testosterone and sertoli cells so the LH/testosterone system and the GnRH/FSH system

Question 16

What is the hormone during pregnancy?

Answer 16

Oestriol

Question 17

What is primary/secondary amenorrhea? Oligomenorrhea?

Answer 17

• primary - never had single period
• seconary - periods that stop
• oligom. infrequent cycles

Question 18

List causes of infertility

Answer 18

• pituitary failure
• prolactinoma
• testicular failure
• ovarian failure
• PCOS

Question 19

Rising oestrogen levels has a negative feedback effect on FSH.

Answer 19

True in the follicular phase of the cycle until the negative feedback loop exerted reduces FSH levels - only the Graafian follicle is able to survive without the FSH –> the graafian follicle continues to produce even more oestrogen (in the absence of progesterone) –> this will then create a POSITIVE feedback loop and so the surge in LH and FSH
If fertalisation does not occur, inhibin, progesterone, E2 (=oestrogen) exert a negative feedback on LH and FSH release, causing luteolysis and menstruation