Male and female reproductive endocrinology Flashcards
Outline the hormonal regulation of sperm production
Hypothalamus - secretion of gonadotrophin releasing hormone (GnRH) into pituitary gland
This stimulates the adenohypophysis to secrete LH and FSH
LH stimulates Leydig cells, in the testes, telling them to produce testosterone.
Testosterone and FSH act on testes to produce sperm
Explain the role of negative feedback and inhibition in sperm production
Sperm production has a negative feedback effect on the anterior pituitary and the hypothalamus causing them to secrete less hormone.
- Inhibition of GnRH, LH, & FSH by testosterone and inhibin
State the effects of testosterone in male foetal development and during puberty
- Secreted in male embryo from testes: causes development of male fetal anatomy
Puberty
- Acne
- Bone growth (via estradiol)
- Sperm production
- Muscle development
- Maturation of genitalia
- Male pattern pubic hair
- Enlargement of larynx
- Increased aggression and libido
How does the production/concentration of testosterone vary during a males lifetime?
Concentration of testosterone in plasma increases significantly during puberty
Production slowly decreases post-40
What, if any, effects does testosterone have in females?
The lack of testosterone in females leads to the development of female anatomy in utero
Same in embryo XY
Outline the hormonal regulation of ovulation
Hypothalamus - secretion of gonadotrophin releasing hormone (GnRH) into pituitary gland
Stimulates adenohypophysis to secrete LH and FSH
LH and FSH stimulates ovaries leading to ovulation (and secretion of oestrogens and progesterone)
Explain the role of negative feedback and inhibition in ovulation
Stimulation of ovaries inhibits the anterior pituitary gland
Ovulation (oestrogen and progesterone) inhibit the anterior pituitary and hypothalamus
State the effects of oestrogen in females
Causes ovulation and menstruation
- Subcutaneous fat deposition
- Female pattern pubic hair
- Maturation of genitalia
- Widening of pelvis
- Breast development
- Fair complexion
- Female psyche
- Bone growth
How does the production of oestrogen vary during a females lifetime?
What is mean age of menopause? Consequence?
Oestrogen secretion post puberty is cyclical, until menopause
On average, women stop producing oestrogen at age 52. This means that they lose the negative feedback causing FSH and LH concentration to increase post-menopause
How is it possible to determine menstrual cycle duration at foetal age?
- Secretion of GnRH is pulsatile and the frequency of secretion determines FSH or LH secretion.
- In foetus, hypothalamus shows pulsatility
- If exposed to testosterone, the pulsatility is disrupted
How long is an average menstrual cycle?
Outline the hormonal changes that occur during 1 menstrual cycle
28 days (bleeding occurs in the first 10 days)
- FSH increases from day 0, plato’s a little around day 7 (1.0mmol/L) and decreases. There is a smaller, sharper peak around day 14
- Oestradiol increase from day 0 to 2.0mmol/L , and decreases by day 14. There is a second rise (peak= 1.5mmol/L) of similar duration
- Progesterone remains low (0.5mmol/L) and rises after day 14 to 50mmol/L. It drops by day 28 to a concentration above all other hormones (10mmol/L)
- LH remains low and spikes at day 14
How does the base oestradiol level vary between women?
Big variation in base level
Some women have few days of month when [testosterone] > [oestrogen]
Why is the LH spike relevant in the menstrual cycle?
It causes oestradiol and progesterone to increase for approximately 7 days
Causes expulsion of ovum
If the bleeding time varies, which part of the menstrual cycle remains constant?
Day 14-28
Consider the menstrual cycle
What happens to the ovarian follicle?
Increases in size gradually until day 14 where the egg is expelled (ovulation occurs 14 days before menstruation)
Follicle size decreases and becomes yellow
Consider the menstrual cycle
What happens to the endometrium?
The lining gradually increases in size. After day 14, it enters the secretory phase which is caused by progesterone. This phase keeps the ovum warm, safe and receiving nutrients.
From approximately day 26, the endometrium collapses due to reduction in progesterone (even a small drop will cause this). Progesterone causes blood vessel constriction causing surrounding cells to die leading to atrophy of the tissue (due to anoxia)
- This causes bleeding
- After 18 hours, the blood vessels dilate allowing for the dead cells to be washed away. This also leads to blood clots
- These undergo fibrinolysis and eventually menstruation (liquified clots and shedded endometrium)
Consider the menstrual cycle
What happens to the cross sectional area of the cervix?
What is the maximum size?
Day 0- large, allows menstrual flow (caused by prostaglandins causing dilation)
Decreases but begins to get bigger by day 14 (it is maximally dilated during ovulation)
Decreases after day 14
3mm
Consider the menstrual cycle
What happens to the cervical mucus
Progesterone causes mucus viscosity to increase, sperm cant swim in, bacteria cant enter (difficult to get pregnant after day 16)
Mucus thickest at day 12 and 16
Consider the menstrual cycle
What happens to body temperature?
Woman is warmest ( 36.8) day after ovulation
Discuss the use of aspirin during menstruation
Atrophy of the endometrium (caused by anoxia) causes the release of prostaglandins which stimulates pain causing cells and uterine contractions (period cramps)
Aspirin is an NSAID and inhibit prostaglandins
State the relationship between day 3 [inhibin-B] and chances of pregnancy
Women with low day 3 serum [inhibin-B] demonstrate a power response to ovulation induction and are less likely to concieve a clinical pregnancy though ART relative to women with increased day 3 [inhibin-B]
