Flashcards in Lecture 6: The Menstrual Cycle Deck (46)
What is the length of the menstrual cycle?
What is the duration of bleeding?
Less than 8 days
What is the HPO axis?
What is the proliferative phase of the menstrual cycle?
The follicular phase
From day 1 – ovulation
Signficance: this is the VARIABLE region where the length of the time can change
Which phase of the menstrual cycle is variable?
The Follicular/Proliferative phase
What are the hormones that are salient in the HPO (HPG axis)?
1. GnRH (hypothalamus)
4. Estradiol (ovary)
5. Progesterone (ovary)
What is the significance of the increase in frequency/amplitude of mid-cycle GnRH pulsatile secretion?
Favors the LH surge necessary for ovulation
How does the pulsatile secretion of follicular phase compare with luteal phase?
Higher frequency and lower amplitude characterizes follicular phase over luteal phase
Luteal phase is less frequent and high amplitude
What secretes GnRH?
GnRH neurons in the hypothalamus
What are the 3 key points of hypophyseal-anterior pituitary relationship in HPO axis?
Point 1: When appropriately stimulated, hypothalamic neurons secrete either releasing or inhibiting hormones to the capillary plexus
Point 2: GnRH travels through the portal veins to the anterior pituitary where they stimulate or inhibit release of hormones from ant. Pituitary
Point 3: Anterior pituitary hormones are secreted in the SECONDARY capillary plexus
What is the acronym for shit released by anterior pituitary?
What is released by posterior pituitary?
What cells secrete FSH and LH in pituitary?
The Gonadotrope cells
What is the significance of the glycosylated polypeptides?
Alpha and Beta chain are located on the following hormones:
What is the significance of LH and hCG?
Same alpha chain, different beta chain
Consequence: LH and hCG can act on same receptor
Help to regulate/mess up menstrual cycle
What is an oocyte?
Germ cells in the ovary
When do women have all their oocytes?
Has supporting cells (granulosa and theca cells) surrounding them
When do follicles begin to be recruited?
20 weeks in utero
What is are the key checkpoints in a woman’s reproductive life?
6-8 weeks: oogenesis begins
16-18 weeks: 6 million oocytes
Birth = 2 million oocytes
Puberty = 300,000 oocytes
Menopause = 0 oocyte
How are follicles recruited?
They are recruited from the primordial stage to the primary stage
Little is known about the initiation
When are follicles gonadotropin dependent?
At the secondary follicle stage
What is the significance of FSH?
1. Stimulates granulosa cell proliferation
2. Stimulates aromatase activity in granulosa cells
-stimulates conversion of androgens to estrogens
3. Upregulates FSH and LH receptors
How is the follicular phase regulated?
Serum estradiol concentrations peaks 1 day before ovulation
Estrogen results in NEGATIVE feedback on pituitary and hypothalamus
Once estradiol reaches a threshold, estrogen feeback becomes STIMULATORY and results in increase in GnRH pulse frequency
-this leads to LH surge
So estrogen can be both inhibitory and stimulatory
What is the LH surge?
Cause release of oocyte from follicle 36 hours after beginning of LH surge
-leads to luteinization of the granulosa cells with increased production of progesterone
-causes resumption of meiosis of the oocyte and release of 1st polar body
How long does it take for egg to pass from fallopian tube to uterus?
When must fertilization occur?
Within 24 hours of ovulation or ovum degenerates
How are the gonadotropins inhibited during luteal phase?
Progesterone and estrogen inhibits their release
What is the function of estrogen?
1. In the luteal phase, inhibits release of gonadotropins initially, then stimulates LH release for ovulation
2. Promotes reconstruction and growth of the endometrium
3. Glands lined by low columnar epithelium cells
4. MITOSES become PROMINENT
What is the function of progesterone?
1. LIMITS growth, mitosis and DNA synthesis
2. Increased tortuosity of glands
-intensified coiling of spiral vessels
3. Secretion of glycoproteins and peptides into cavity