Menstrual Cycle and Ovulation (Creamer) Flashcards
What are the two organs primarily involved in the menstrual cycle
Ovaries & Uterus
What are the stages of development of the ovarian follicle
- Follicular phase
- Ovulatory phase
- Luteal phase
What state is the gamete in as a primordial follicle
Primary oocyte arrested in Prohase I
What surrounds a primordial follicle
Single layer of preganulosa cells
What does a primary follicle consist of
Growing primary oocyte surrounded by a single layer of cuboidal shaped granulosa cells & early zona pellucida (ZP1-ZP4)
What makes up a secondary follicle
Growing primary oocyte surrounded by zona pellucida, 3-6 layers of cuboidal granulosa cells & thecal cells
What is the function of the zona pellucida
Provides a binding site for sperm durng fertilization
What receptors do granulosa and thecal cells express on their surface?
How do they grow before they start producing ovarian hormones?
Granulosa - FSH receptors
Thecal - LH receptors
They depend on paracrine factors from the oocyte and surrounding cells for growth
What is the dense mass of granulosa cells that surrounds the oocyte after the formation of the antrum
Cumulus oophorus/corona radiata
During antral development what are the two populations of granulosa cells that are formed
- Mural/stratum granulosa (outer wall of follicle that become highly steroidogenic)
- Corona radiata/cumulus oophorus (released during ovulation with oocyte)
At what stage does the follicle become responsive to gonadotropins
Devlopment of the antrum
What hormone do thecal cells respond to & what is the response
LH
Androgen synthesis from acetate and cholesterol (primarily androstenedione)
What hormone do granulosa cells respond to & what is the response
FSH
Converts androgens (androstenedione) from thecal cells to estrogen
Why do granulosa cells upregulate LH receptors before ovulation
LH triggers granulosa cells to secrete more inhibin which inhibits FSH secretion. Decreased FSH allows for the establishment of the dominant follicle.
What makes an oocyte competent to finish meiosis I at ovulation?
During the antral phase, the follicles become large which allows the oocyte to synthesize sufficient amounts of cell cycle components (CDK-1 and cyclin B) but they stay arrested until the large LH surge
How is meiotic arrest achieved even though the large antral follciles gain meiotic competence
Maintenance of elevated cAMP levels keeps the follicle arrested in Prophase I
How is the dominant follicle selected?
Mural granulosa cells produce low levels of estrogen and inhibin which will decrease FSH levels. Largest follicle with the most FSH receptors becomes the dominant follicle.
The dominant follicle becomes a large preovulatory follicle known as Graffian follicle
What is the periovulatory period
Time between LH surge and ovulation ~32-36 hours
What are the effects of luteinization on theca and granulosa cells
- During the LH surge both thecal and granulosa cells have LH receptors.
- Inhibition of aromatase expression and estrogen production
- Low levels of LH promotes progesterone production
What structural changes are seen with an LH surge?
OVULATION
1) Breakdown of follicle wall, tunica albuginea, and surface epithelium
2) Cumulus-oocyte detaches and floats in antrum
3) Basal lamina degraded
4) Oocyte continues into meiosis (arrests in metaphase II)
What is the corpus luteum?
temporary structure in ovaries
- Produces progesterone and moderate levels of estradiol and inhibin
- Remains of ovarian follicle that released a mature ovum during during ovulation
- Often yellow due to carotenoid pigments
What is corpus albicans?
Regressed form of the corpus luteum.
- No fertilization occurs: corpus luteum is broken down by macrophages
- Fibroblasts lay down type collagen
- Remains may persist as a scar on the surface of the ovary
How does the corpus luteum stay viable?
If fertilization occurs, hCG rescues corpus luteum and will be viable for duration of pregnancy
What is the function of the corpus luteum in pregnancy?
Produces increasing amount of progesterone
- Transforms uterine lining into supportive structure important for implantation
- Low levels of LH
- Secrete inhibin A to suppress FSH
