Endo 10 - Gonads 2 Flashcards
What is the weak androgen produced by both the adrenals and the gonads?
Androstenedione
What two reactions can testosterone follow and what do they produce?
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.
How is testosterone and DHT transported in the blood?
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
How is testosterone and DHT transported in the seminiferous tubules?
Bound to androgen binding globulin (ABG)
What are the effects of androgens in the foetus and in adults?
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
Define oestrogen.
Any molecule that induces mitosis in the endometrium.
Examples
17beta-oestradiol (main)
oestrone (precursor)
What is the main oestrogen in the menstrual cycle?
17 beta oestradiol
What are the actions of oestrogens?
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
Define progestogen.
Any molecule that induces secretory changes in the endometrium
What are the actions of progestogens?
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
Which cells in the testes have receptors for FSH and LH?
Sertoli Cells - FSH - secrete inhibin
Leydig Cells - LH - secrete testosterone
Describe the negative feedback from the testes to hypothalamo-pituitary axis
Sertoli Cells - produce INHIBIN - negative feedback effect on hypothalamus and pituitary
Leydig Cells - produce TESTOSTERONE - negative feedback effect on hypothalamus and pituitary
How do these pathways cause negative feedback?
Decreases the AMPLITUDE of the GnRH pulses.
Spermatogenesis requires what to be complete?
Both testosterone and sertoli cells so the LH/testosterone system and the GnRH/FSH system
Spermatogenesis requires what to be complete?
Both testosterone and sertoli cells so the LH/testosterone system and the GnRH/FSH system
What is the hormone during pregnancy?
Oestriol
What is primary/secondary amenorrhea? Oligomenorrhea?
- primary - never had single period
- seconary - periods that stop
- oligom. infrequent cycles
List causes of infertility
- pituitary failure
- prolactinoma
- testicular failure
- ovarian failure
- PCOS
Rising oestrogen levels has a negative feedback effect on FSH.
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
