Female Reproductive Physiology - Trachte Flashcards
How many chromosomes are in Primary Oocytes?
46
How many chromosomes are in Secondary Oocytes?
23
How many chromosomes are in an Ovum?
23
At what stage is oogenesis arrested in the developing fetus?
Prophase I of Meiosis I
At what stage is oogenesis arrested in during ovulation?
Metaphase II of Meiosis II
Are quiescent eggs in the ovary diploid or haploid?
Diploid
they don’t get to haploid until fertilization
What type (first, second, third) of follicles do primary oocytes reside in?
All three:
Primary oocytes reside in Primary, Secondary and Tertiary Follicles
Where does the majority of progesterone come from?
Corpus luteum (after ovulation)
What degrades the Corpus Luteum?
Prostaglanding F2-alpha
used in agriculture to synchronize cycles of animals
What are the seven basic steps in the Summary of Ovarian Follicular Development?
- At birth all oogonia have developed into primary oocytes which represent the total complement of oocytes available to the female during her reproductive life
- Primary oocytes are surrounded by “follicular cells”= granulosa & thecal cells: collectively called primordial follicles.
- Primordial follicles slowly progress to primary follicles and a large number survive until menopause (~50yrs).
- When primoridal/primary follicles are exhausted: menopause ensues.
- Each cycle a cohort (
When does menopause begin?
When all primordial/primary follicles are exhausted
What are the components of the Mature Hypothalamo-
Pituitary Ovarian Axis?
Hypothalamus => secretes GnRH
Anterior Pituitary => secretes FSH and LH
Ovaries => Granulosa cells stimulated by FSH and produce Inhibin, Theca cells stimulated by LH and produce androgens (converted to estrogen by aromatase in granulosa cells)
Negative Feedback:
Inhibin inhibits FSH (pituitary)
Estrogen inhibits GnRH (hypothalamus) and LH (pituitary)
What is different about the negative feedback inhibition in the Hypothalamo-Pituitary Ovarian Axis during ovulation?
Estrogen is no longer negative feedback => becomes positive feedback (activates release of GnRH and LH)
***Causes LH surge and ovulation!
(Inhibin inhibits FSH from causing more follicle maturation)
What happens to the Hypothalamo-Pituitary Ovarian Axis during Menopause?
No estrogen
High GnRH, FSH, and LH
What happens to the Hypothalamo-Pituitary Ovarian Axis during pregnancy?
Tons of estrogen
Low GnRH, FSH, and LH
***Under control of the placenta (secretes estrogen, progesterone, and bHCG)
What hormone stimulates LH during pregnancy?
beta-hCG
also maintains corpus luteum
What type of receptor does GnRH act on?
G-Protein coupled, Gq
Gq => Activates phospholipase C => DAG => IP3
Why is the secretion of GnRH pulsatile?
So that you do not sensitize the downstream receptors and shut off the axis
(Pulsatile release essential for normal gonadal response, constant release will shut down the system)
What hormone is released by the placenta? What are the effects of it?
In first trimester hCG maintains corpus luteum which keeps progesterone (and estrogen) levels high to maintain pregnancy.
Stimulates LH receptor
In later pregnancy the placenta takes over steroidogenesis and pregnancy maintenance.
What type of receptors do FSH/LH act on?
Gs-protein coupled receptors => adenyly cyclase => increased cAMP
What hormone is made in luteal cells?
Progesterone (via pregnenolone)
What converts testosterone to estradiol?
Aromatase
What receptors does Estrogen acts on?
acts on receptors in cytosol (ER-alpha) => translocate into the nucleus => modulate transcription
What are the physiologic effects of Estrogen?
Facilitate growth of ovarian follicles; increase motility of uterine tubes; increase uterine muscle
Increased libido
Breast duct growth and enlargement (at puberty)
Female secondary sex characteristics
Salt & water retention
What happens with the hormone levels during the follicular phase?
Small increases in the secretion of gonadotropins (LH & FSH) lead to follicular growth, including an increase in the synthesis and secretion of ovarian steroid hormones.
Estrogen becomes positive feedback stimulator in late follicular phase/ovulation.
What happens with the hormone levels during the luteal phase?
Very high levels of Estrogen provoke changes in GnRH secretion pattern to manifest rapid pulses.
This stimulates a surge in LH which induces resumption of meiosis in the dominant follicle as well as ovulation.
Ovulation induces luteinization which is characterized by the formation of the corpus luteum which produces high levels of progesterone and estrogen.
What happens to the hormone levels when the corpus luteum dies?
Decreased Estrogen and Progesterone secretion. Decreased negative feedback inhibition.
Increase in GnRH and FSH/LH secretion.
What happens if you prevent the LH surge?
Prevent ovulation.
Hormonal contraceptives suppress the LH surge.
What controls the uterine phase (i.e. proliferation/menses)?
The ovarian cycle.
Estrogen causes thickening and proliferation of the endometrium.
Progesterone halts further growth of endometrium =>
causes secretion from glands, rather than proliferation of glands.
What produces beta-hCG?
beta-hCG = gonadotropin produced in the chorion that has luteotropic activity (supports the corpus luteum)
What would happen if you remove the ovaries (oophorectomy) at ~ 15 weeks gestation?
does not terminate pregnancy as corpus luteum is not necessary for the production of Progesterone & Estradiol after the first trimester
When does the placenta take over secreting estrogen/progesterone in pregnancy?
The critical transition between uterine dependence on ovarian versus placental steroids occurs at the end of the first trimester, an interval with the greatest likelihood of miscarriage.
What is the importance of higher levels of progesterone compared to estradiol early in pregnancy and then later higher leves of estradiol compared to progesterone in late pregnancy stages?
Progesterone > Estradiol:
- Progesterone causes hyperpolarization of myometrial cells which prevent contractions.
- Decreases adrenergic receptors
- Inhibits oxytocin receptor synthesis
- Inhibits Estrogen receptor synthesis
- Promotes storage of Prostaglandin synthesizing enzymes.
Estradiol > Progesterone:
- Increases Oxytocin receptors
- Promotes uterine contractility
- Cervical “ripening”
- Increases local prostaglandin release from the placenta -which causes myometrial contractions.
- Oxytocin release from the posterior pituitary which stimulates more and stronger myometrial contractions.
What is the importance of prostaglandins in pregnancy?
PGF2 and PGE2 predominate in reproduction
Involved in rupture of the Graafian follicle at ovulation, contraction of myometrium during menstruation
Responsible for the mild Braxton Hicks contractions during pregnancy.
Important in strong uterine contractions during parturition.
Produced in placental unit .
What is the importance of Oxytocin in pregnancy?
Induces smooth muscle contractions in the uterus.
Mechanical stimulation of the cervix at end of gestation causes Oxytocin release.
Forceful uterine contractions during parturition also induces Oxytocin release
What hormones are important in mammogenesis?
Development of epithelial ductal tree
***Estrogen, glucocorticoids, GH (somatropin) dependent
Add progesterone and prolactin and get lobular-alveolar growth
What hormones are important in lactogenesis during mid-late pregnancy?
Lobular-alveolar growth
***Estradiol, glucocorticoids, prolactin, progesterone, and placental lactogen
What hormones are important in post-partum lactogenesis?
Onset of copious milk secretion comes with the fall of progesterone with parturition.
Ensues with parturition
Removal of the placenta (which removes source of progesterone), ***IF retained placenta-no milk secretion!
Prolactin dependent
What hormone is critical for Galactopoiesis: maintenance of lactation?
Prolactin
What hormone is critical for Milk ejection/let down?
Oxytocin
