3. Male and female reproductive endocrinology Flashcards
Testosterone
androgen which is secreted in response to LH secretion
Stimulates testes to cause sperm production
FSH also acts on testes to cause sperm production
What regulates testosterone secretion
In order for sperm production to occur there must be testosterone, and in order for testorone to be secreted there must be LH
Testosterone negative feedbacks to inhibit LH and FSH secretion
Inhibin also causes therapeutic feedback, but isn’t used therapeutically in males
Embryology reproductive endocrinology
In male embryo, testes secrete testosterone which causes development of male feotal/embryonic development
In the female, oestrogens have no effect and there is no testosterone, so females develop female anatomy
Default situation is female anatomy
Testosterone in puberty
Massive increase in testosterone secretion in puberty
Causes male secondary sexual characteristics
Once puberty starts, testosterone levels are maintained until about 40 when they decrease, but never stop
secondary sexual characteristics remain in males until they die
Secondary characteristics as a result of testosterone
Increased aggression and libido* - effects of testosterone on the brain
Enlargement of the larynx - voice breaks
Male pattern pubic hair - also facial hair, chest hair
Maturation of genitalia
Muscle development - due to anabolic steroids
Sperm production
Bone growth* - long bone growth - arms and legs
Acne - increased sebaceous gland activity
*some effects of testosterone require conversion to oestradiol by aromatase
Female reproductive endocrinology
GnRH causes LH and FSH release
LH and FSH cause ovulation - oestrogens and progesterone released
Progesterone and oestrogen negative feedback of GnRH
Oestrogens (e.g. oestradiol) to do with ovulation
Progesterone acts for and behalf of pregnancy
Progestogens are progesterone like hormones
Oestrogens negative feedback on FSH
Progesterone negative feedback on LH
In foetus, lack of male hormones (testosterone) results in female characteristics
In puberty, lack of male hormones result in secondary sexual characteristics. Usually around 11-12 until 17-18
Female secondary sexual characteristics
Bone Growth - long bone growth so increase in stature
Female psyche - more likely to have more caring type personality
Fair complexion
Breast Development
Widening of the pelvis
Maturation of genitalia
Female pattern pubic hair - no facial or chest hair growth
Subcutaneous fat deposition - instead of muscle growth caused by androgens
Ovulation and menstruation
Hormones during menstrual cycle
GnRH causes secretion of FSH and LH which cause oestrogen and progesterone secretion
First half of menstrual cycle is oestrogen dominant
Second half of menstrual cycle is progesterone dominant
GnRH secretion in females
In females, GnRH secretion is pulsatile and not constant, and the frequency of that pulsatile secretion determines whether you have FSH secretion or LH secretion.
It depends on number of GnRH secreted per day. This pulsatility depends on the part of the month, can be slow at one part or quick at another.
Slow production causes FSH production and rapid causes LH production.
In a female foetus with XX chromosome, the pulsatility of the hypothalamus is there before the baby is born. This means that duration of menstrual cycle is built into the feotus.
If a female feotus is exposed to testosterone or androgens, she loses the pulsatility of the GRH release, and becomes like a male
Menopause
At age 52 women stop secreting eostrogen etc and undergo loss of secondary sexual characteristics. Not a depletion, a endocrine event Bone Growth Female psyche Fair complexion Breast Development Widening of the pelvis Maturation of genitalia Female pattern pubic hair Subcutaneous fat deposition Ovulation and menstruation
Ovulation
Average length of ovulation is 7 days
Increase in FSH concentration
In response to increased FSH, oestrogen concentrations also start to rise
Oestrogens exert negative feedback over FSH, so FSH levels dip and so do oestradiol levels
on about day 12 of the menstrual cycle, get a LH surge, and a little FSH surge (which has no function and may be accidental and accompanies the LH surge)
LH surge during menstrual cycle
The signal for the LH surge requires 36 hours of elevated oestradiol, which positively feedbacks the LH
LH causes progesterone secretion plus some oestradiol secretion.
This LH surge is sufficient to generate progesterone and eostradiol for about 7 days, then start to tail off by the end of the month.
What hormone can pop up midcycle in some women?
For some women, small amount of testosterones become dominant midcycle because oestradiol and progesterone dip so much.
Results in acne mid-cycle.
FSH and egg maturation
FSH causes follicle to mature and as it does, it secretes oestrogens.
During that maturation, the ovum moves to the edge of the follicle and the LH surge causes ovulation. LH surge causes egg to be expelled.
Takes two days for LH to produce its effect. Under influence of LH the remaining cells of the empty follicle turn yellow and secrete loads of progesterone and a bit of oestradiol.
LH is only promoting secretion for 7 days after this secretion falls to 0. second half of cycle is constant, and ovulation occurs 14 days before the first day of the menstrual cycle.
Oestradiol
Oestradiol has a thickening effect on the endometrium
When progesterone acts on the endometrium, it causes it to secrete nutrients. When the ovum is ready, it can grow in the endometrium which is warm, thick and nutritious.
Assuming that ovulation does not result in conception, then after 7 days the secretory phase decreases, and the endometrium which has grown because of oestrogen and progesterone, will start to collapse. Any drop in progesterone (regardless of amount) will trigger collapse of the endometrium.
