Sex Hormones Flashcards
(24 cards)
what is the first step in sex hormone formation?
*release of the Gonadotropin releasing hormone (GnRH) from the hypothalamus
*GnRH is released in a PULSATILE fashion
what is the effect of continuous administration of GnRH?
causes a decrease in FSH/LH
where are FSH and LH released from?
from the anterior pituitary gland in response to GnRH
what does LH and FSH do in males?
LH- stimulates leydig cells which causes testosterone synthesis and eventually spermatogenesis
FSH- stimulates sertoli cells which triggers spermatogenesis
what does LH and FSH do in females?
LH- stimulates theca cells which cause androgen synthesis which aids in the production of estrogen
FSH- stimulates granulosa cells which causes aromatase activation which leads to estrogen production
what is the negative feedback loop in puberty?
*Testosterone inhibits Hypothalamic GnRHand pituitary FSH/LH secretion
* Estrogen:
↓ FSH/ ↓ LH, May also ↓GnRH
* High levels increase LH (LH surge)
* Estrogen + Progesterone:
estrogen effect multiplied
* Progesterone alone may ↓GnRH pulse frequency
↓ Anterior pituitary responsiveness to GnRH
what causes puberty?
- It is initiated by hormonal signals from the brain to the gonads (HTH-P-G axis)
- Hypothalamus less sensitive to gonadal steroids
what are some of the androgens?
- Testosterone
- Androstenedione
- Dihydrotestosterone (DHT)
The precursor of all estrogens (oestrogens)
what are the actions of androgens?
*stimulate spermatogenesis
*development of secondary sexual characteristics e.g., increase in height and wight, growth of pubic/ facial hair and body odour
what is the action of Dihydrotestosterone?
- embryogenesis -> Formation of gonads
- DHT produced locally (hair follicles) -> DHT -> Alopecia (androgenetic alopecia)
what is oestradiol?
- Receptors in brain, penis, and testis
- Sexual appetite
- Erection
- Spermatogenesis
what is the effect of the female hormone cycle and what is it controlled by?
*It effects the periodicity of the ovulation
*It is controlled by the hypothalamic-pituitary- gonads axis
what are the phases that the ovaries and endometrium go through in a normal menstrual cycle?
The ovaries go through 3 phases:
1. Follicular.
2. Ovulation.
3. Luteal.
The endometrium goes through 3 phases:
4. Proliferative.
5. Secretory.
6. Menstruation.
what are the three phases in the follicular phase?
Recruitment:
*FSH -> maturation of a cohort of ovarian follicles-> only one reaches maturity
Maturation of the follicle:
* Maturation of primordial follicles into primary follicles
Selection:
*As the follicles mature -> increase estrogen -> decrease FSH“-ve feed back on the pituitary”
*->the follicle with the highest number of FSH receptors will be selected The other follicles “that were recruited” will become atretic (breakdown)
what is the negative/positive feedback on the pituitary in the minstrel cycle?
Negative:
- increase in Estrogen (estradiol) -> - feed back on pituitary-> decrease FSH
Positive:
- increase estradiol (reaching a threshold concentration) -> + feed back on the pituitary -> LH surge ->ovulation
Describe the LH surge
- Lasts for 48 hrs
- Ovulation occurs after 36 hrs
- Accompanied by rapid fall in estrogen level
- Granulosa cells -> luteinization -> progesterone synthesis
- Affects follicular wall -> follicular rupture
What happens in the Luteal Phase?
- Now empty follicle changes to a yellow colour, becomes corpus luteum
- Continues to secrete estrogen, but now beings to release progesterone
- Progesterone further develops uterine lining
- If pregnancy occurs -> Human chorionic gonadotropin (hCG) secretion -> maintain the corpus luteum
Whare is hCG secreted from initially?
Initially secreted by the trophoblast layer of the developing blastocyst
What is the function of hCG?
- hCG behaves like FSH and LH but it is NOT inhibited by a rising level of progesterone.
- hCG prevents the deterioration of the corpusluteum at the end of the fourth week.
- Enables pregnancy to continue.
what happens if no embryo is produced?
*the corpus luteum begins to disintegrate
* Progesterone levels drop, uterine lining detaches, menstruation can begin
* Tissue, blood, unfertilized egg all discharged
* Can take from 3-7 days
what occurs in menstruation?
- Periodic desquamation of the endometrium
- Prostaglandins are maximal in the endometrium just before menses
- Prostaglandins -> constriction of the arterioles->ischemia & desquamation Followed by arteriolar relaxation, bleeding & tissue breakdown
How can hCG be used to detect pregnancy?
Rapid rise of hormone in woman’s urine after 7-10 days
It is a peptide hormone
what are the oral contraceptives?
*combined oral contraception (COC)- contains both estrogen and progesterone
*progesterone only pill (POP)
what mechanism of actions do oral contraceptives use?
estrogen and progesterone inhibit GnRH preventing FSH release, the mid-cycle surge of LH and ovulation. this means that there is no egg to furtilize
