Sex Hormones

Question 1

what is the first step in sex hormone formation?

Answer 1

*release of the Gonadotropin releasing hormone (GnRH) from the hypothalamus
*GnRH is released in a PULSATILE fashion

Question 2

what is the effect of continuous administration of GnRH?

Answer 2

causes a decrease in FSH/LH

Question 3

where are FSH and LH released from?

Answer 3

from the anterior pituitary gland in response to GnRH

Question 4

what does LH and FSH do in males?

Answer 4

LH- stimulates leydig cells which causes testosterone synthesis and eventually spermatogenesis
FSH- stimulates sertoli cells which triggers spermatogenesis

Question 5

what does LH and FSH do in females?

Answer 5

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

Question 6

what is the negative feedback loop in puberty?

Answer 6

*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

Question 7

what causes puberty?

Answer 7

• It is initiated by hormonal signals from the brain to the gonads (HTH-P-G axis)
• Hypothalamus less sensitive to gonadal steroids

Question 8

what are some of the androgens?

Answer 8

• Testosterone
• Androstenedione
• Dihydrotestosterone (DHT)
  The precursor of all estrogens (oestrogens)

Question 9

what are the actions of androgens?

Answer 9

*stimulate spermatogenesis
*development of secondary sexual characteristics e.g., increase in height and wight, growth of pubic/ facial hair and body odour

Question 10

what is the action of Dihydrotestosterone?

Answer 10

• embryogenesis -> Formation of gonads
• DHT produced locally (hair follicles) -> DHT -> Alopecia (androgenetic alopecia)

Question 11

what is oestradiol?

Answer 11

• Receptors in brain, penis, and testis
• Sexual appetite
• Erection
• Spermatogenesis

Question 12

what is the effect of the female hormone cycle and what is it controlled by?

Answer 12

*It effects the periodicity of the ovulation
*It is controlled by the hypothalamic-pituitary- gonads axis

Question 13

what are the phases that the ovaries and endometrium go through in a normal menstrual cycle?

Answer 13

The ovaries go through 3 phases:
1. Follicular.
2. Ovulation.
3. Luteal.
The endometrium goes through 3 phases:
4. Proliferative.
5. Secretory.
6. Menstruation.

Question 14

what are the three phases in the follicular phase?

Answer 14

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)

Question 15

what is the negative/positive feedback on the pituitary in the minstrel cycle?

Answer 15

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

Question 16

Describe the LH surge

Answer 16

• 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

Question 17

What happens in the Luteal Phase?

Answer 17

• 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

Question 18

Whare is hCG secreted from initially?

Answer 18

Initially secreted by the trophoblast layer of the developing blastocyst

Question 19

What is the function of hCG?

Answer 19

• 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.

Question 20

what happens if no embryo is produced?

Answer 20

*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

Question 21

what occurs in menstruation?

Answer 21

• 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

Question 22

How can hCG be used to detect pregnancy?

Answer 22

Rapid rise of hormone in woman’s urine after 7-10 days
It is a peptide hormone

Question 23

what are the oral contraceptives?

Answer 23

*combined oral contraception (COC)- contains both estrogen and progesterone
*progesterone only pill (POP)

Question 24

what mechanism of actions do oral contraceptives use?

Answer 24

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