Discussing the menstrual cycle stages and changes before and after ovulation.
Events described as pre-ovulatory (before ovulation) and post-ovulatory (after ovulation).
Importance of ovary and changes in follicle development, and changes in the uterus.
Follicular Development
Starting with primordial follicles which develop into primary follicles.
Primary oocyte in follicles is arrested in diplotene stage (prophase I of meiosis).
Single layer of small cells called follicular cells surrounds the oocyte.
From Primary to Secondary Follicle
Primordial follicle develops into primary follicle.
Secondary follicle forms as multiple layers of granulosa cells surround the oocyte.
Formation of glycoprotein layer called zona pellucida between oocyte and granulosa cells.
Theca cells form outside the granulosa cells.
Formation of Tertiary Follicle
Secondary follicle evolves into tertiary (vesicular) follicle with an antrum cavity filled with fluid.
Granulosa cells support the oocyte and produce estrogen from androgen (from theca cells).
Formation of cumulus oophorus (group of cells suspending the oocyte) and increase in theca cells around the follicle.
Hormonal Control and Regulation
FSH (Follicle-Stimulating Hormone): Initiates development of the follicles.
LH (Luteinizing Hormone): Works with FSH for follicular growth and maturation.
Estrogen: Produced by granulosa cells, essential for the proliferation of endometrium in the uterus.
Inhibin: Produced by granulosa cells, negatively regulates FSH levels.
Pre-Ovulation Events
Follicular phase includes the development of follicles from primary to Graafian follicle generally from day 6 to day 14 in the cycle.
Increased estrogen produced by developing follicles leads to a negative feedback on FSH and LH initially.
Dramatic change near ovulation causes a surge in LH (known as LH surge) due to positive feedback from high estrogen levels.
LH surge results in completion of meiosis-I in the oocyte and start of meiosis-II, leading to the formation of a secondary oocyte and the first polar body.
Endometrial Changes
Estrogen stimulates the regeneration and proliferation of endometrium which thinned during menstrual flow.
This phase is termed as proliferative phase of the menstrual cycle.
Ovulatory and Luteal Phases
Post-ovulation changes will be detailed in the next lecture.
LH surge triggers ovulation, the release of the secondary oocyte from the Graafian follicle.
Post-ovulation follicle transforms into corpus luteum, producing progesterone for the maintenance of the endometrium.
Conclusion
Understanding of follicle development, hormonal changes, and preparation of the uterus in the menstrual cycle.
Next session to explore post-ovulatory events and the role of corpus luteum.