4/7 Basic Rev of Principles of Repro + Menst Cycle VIDEO Flashcards
The maximum number of oocytes is present when? drops when?
The maximum endowment of oocytes is present at birth and drops with time (at 40-50 y)
Note dropoff in #oocytes from 20 wks gestation to birth!
Spermatogenesis begins when?
Spermatogenesis begins at puberty and continues throughout the lifetime.
If you give an adult woman a constant infusion of GnRH, what would you see in terms of changes to her FSH levels?
Her FSH would rise immediately, but ultimately would fall and be suppressed – due to downregulation of the number of GnRH receptors.
what is the driver of the H-P-A axis? what kind of secretion is required for normal repro function?
The arcuate nucleus and its production of GnRH is the driver of the hypothalamic-pituitary-gonadal axis.
Pulsatile secretion of GnRH is required for normal reproductive function.
At puberty, what part of the HPA axis matures/awakens for proper functioning of reproduction?
“awakening” of the arcuate nucleus (within the hypothalamus)
GnRH: what is it also called? what hormones does it stimulate?
GnRH aka LHRH
Stimulates both LH and FSH from the anterior pituitary
stimulates LH >>> FSH
What does FSH stimulate in the female? male?
Female: FSH stimulates Granulosa Cells in the ovary –> follicular development
Male: FSH stimulates seminiferous tubules
Bottom line: FSH –> germ cell production in both F and M.
What does LH stimulate in the female? male?
Female: LH stimulates the theca cells in the ovary to convert cholesterol to androgens
Male: LH stimulates the Leydig cells to produce testosterone
How do we use GnRH agonists for therapeutic treatment?
Can give a GnRH agonist in order to shut off the HPO circuit.
ex: endometriosis, if we want to decrease the amount of systemic estrogen. Works because the pituitary will be desensitized to GnRH (downreg of GnRH receptors)
If GnRH is suppressed, what happens to levels of LH and FSH?
Pituitary will release NO LH
some FSH (some FSH is secreted regardless of GnRH levels)
A 4 yo boy has an androgen producing tumor. What will happen to his LH levels compared with his pre-tumor levels?
LH will be lower than pre-tumor levels
(Too much testosterone will suppress GnRH production in the hypothalamus due to negative feedback)
The HPG axis is under the primary control of positive or negative feedback?
Negative
For the LH surge and subsequent ovulation, is positive or negative feedback required?
Postive feedback.
If a woman loses all of her follicles (due to radiation or something), will she still have any oocytes? any estrogen production?
She will have neither oocytes or estrogen production
These are linked in one compartment (the follicle) in the female system. Loss of follicle = loss of ability to make estrogen and loss of ability to reproduce
What does the theca cell do? What stimulates it?
In the ovary, Theca cell is stimulated by LH.
Converts cholesterol into androgens
What does the Granulosa cell do? What stimulates it?
In ovary, Granulosa cell aromatizes androgen to estrogen and then to estradiol.
Stimulated by FSH
(remember which is which because F and G are next to each other in the alphabet
FSH –> Granulosa cell
LH –> Theca cell)
where do the proceses of spermatogenesis and androgen production take place?
in the testes
Generally are spermatogenesis and androgen production in the male linked?
What could affect both processes?
Generally these two processes are separate - men can have normal androgen levels alongside abnormal spermatogenesis
Could both be affected with a tumor in the hypothalamus or pituitary, or a genetic cause like Klinefelter’s
In the male, what does FSH do?
In the testis, FSH stimulation of seminiferous tubules (with initiation of spermatogenesis) causes the initial increase of testicular size at puberty (first sign of puberty in males).
In the male, what does LH do?
In testis: LH Stimulation of Leydig Cells causes 10 fold increase in testicular testosterone production (later in puberty).
Leydig cells constitute < 10% of adult testicular mass
Describe the axis which causes spermatogenesis in males.
(Hypothal –> GnRH –> Pituitary ….etc)
(axis on the left)
Describe the axis which causes androgen production in males.
(Hypothal –> GnRH –> Pituitary etc)
(axis on the right)
How long is a normal (ovulatory) menstrual cycle?
How long is the follicular phase?
how long is the luteal phase?
normal/ovulatory cycle = 21-35 d (mean is 29d)
Follicular: variable length
Luteal: ALWAYS 14d +/- 2d
If a woman makes too much estrogen (or makes normal estrogen but no progesteron), what is she at risk for?
If woman makes nothing but estrogen, precursor to endometrial cancer.
Overgrowth of estrogen –> overgrowth of endometrium –> endometrial cancer.
Progesterone is needed to prevent this overgrowth.
Two parts of the menstrual phase? what are they alternatively called?
what event divides them?
Follicular (aka Proliferative)
Luteal (aka Secretory)
Divided by Ovulation
What marks the start of the follicular phase? the end?
Start = onset of menses
End = Ovulation
What marks the start of the luteal phase? the end?
Start = ovulation
End = onset of menses
During the Follicular phase, what generally is going on?
A batch (cohort) of follicles reach the point of maturation where they are Gn-sensitive.
One is selected as dominant - that one will mature and ovulate.
The others undergo atresia/die off.
How is one follicle determined to be the dominant one in its cohort?
There’s competition for FSH that allows a dominant follicle to emerge based on its having more FSH receptors than the others.
The smaller follicles die off due to lack of FSH
After ovulation, what happens to the dominant follicle?
It becomes the Corpus Luteum, lasts for the duration of the cycle.
Secretes progesterone.
What generally is going on during the Luteal phase?
Corpus Luteum (former dominant follicle) is secreting progesterone.
If the Corpus Luteum does not get hCG by day 9 of Luteal phase, it stops producing estrogen and progesterone and dies.
In the context of reproduction, what do these numbers represent?
- 5 days
- 250 (units?)
- 12 hrs
- 40 hrs
- 9 days
- 14 days
- 5 days = time for a dominant follicle to emerge from its cohort
- 250 (units?) = Peak estrogen level: causes LH surge
- 12 hrs = Time between peak estrogen level and LH surge
- 40 hrs = Time from LH surge to follicle rupture and ovulation
- 9 days = if Corpus Luteum is not exposed to hCG within 9 days after ovulation, it will stop producing est and progest and die.
- 14 days = Max time the Corpus Luteum can survive without exposure to hCG. Also length of Luteal phase
During the follicular phase, what is the effect of estrogen on the endometrium?
Estrogen stimulates the production of estrogen and progesterone receptors on the endometrium.
The effect of estrogen on the estr receptors –> proliferation of the endometrium (“Like watering a field of grass”)
What is the dominant hormone during the Luteal phase? what does it do?
Progesterone dominates during Luteal phase.
It limits the number of receptors on the endometrium and thereby halts endometrial growth.
Also causes endometrial cells to become secretory
(creating secretions needed for implantation)
In the absence of a pregnancy, what happens with estrogen and progesterone levels?
what is the result?
No pregnancy –> estrogen and progesterone levels decline
Causes production of Prostaglandins –> arteriolar spasm –> shedding of endometrium –> menstrual period.
Bottom line: withdrawal of progesterone at end of luteal phase –> menses)
What are signs that a cycle is ovulatory?
- cycles lasting 21-35 days are almost always ovulatory
- Breast tenderness, bloating indicates presence of progesterone
- Menstrual cramps - produced by ovulatory endometrium
- Increased basal body temp - during Luteal phase, can rise as much as one degree with ovulation.
(Also rises in first trimester of preg.!!)
Describe theh general behavior of progesterone over the menstrual cycle.
Progesterone: secreted from the Corpus Luteum.
Low during Follicular Phase.
Slow rise and fall during Luteal phase.
General behavior of Estrogen during menstrual cycle?
Estrogen is secreted by the dominant follicle.
Peaks at the end of the Follicular phase (at a level of approx 250). Causes LH surge 12 h later.
With demise of Corpus Luteum, estrogen has its nadir (lowest point), causing FSH to rise mid-Luteal phase.
Rising FSH stimulates a new corhort of follicles, which will secrete estrogen
General behavior of LH during the menstrual cycle?
LH surges 12 h after the Estrogen peak, causing ovulation and the onset of the Luteal phase
General behavior of FSH during the menstrual cycle?
Peaks at same time as LH (but to lesser degree)
with low estrogen at the start of the Follicular phase, FSH levels rise and stimulate estrogen release from the cohort of follicles.
