Early Embryology Flashcards
What are oogoniums?
Diploid (2n) stem cells.
What happens to oogoniums during pre-puberty?
They are converted into primordial follicles (which are arrested in prophase I)
What stimulates primordial follicles to develop into primary follicles?
Localized androgens at puberty
Describe a primary follicle.
Contains a primary oocyte, frozen in prophase I, surrounded by a single layer of granulosa cells.
What hormone stimulates the conversion of a primary follicle to an early secondary follicle?
Follicle-stimulating hormone (FSH).
What does FSH stimulate in the primary follicle?
Proliferation of granulosa cells and formation of the zona pellucida around the oocyte.
How is oestrogen produced by LH and FSH?
LH stimulates theca cells to convert cholesterol into androgens, which are converted into oestrogen in granulosa cells by FSH stimulation.
Describe an early secondary follicle.
Contains a primary oocyte with a zona pellucida, arrested in prophase I, surrounded by multiple layers of granulosa cells.
What additional development occurs in the late secondary follicle?
Formation of pockets of follicular fluid containing hyaluronic acid.
Describe the transformation from the late secondary follicle to the Graafian follicle.
FSH stimulates granulosa cells to produce more follicular fluid, merging pockets into a single cavity called the antrum.
Describe a Graafian follicle.
Contains a secondary oocyte arrested in metaphase II, with an antrum filled with follicular fluid and surrounded by the corona radiata.
What is the corona radiata?
Cells directly wrapping around the secondary oocyte
What are the overall products of the follicular phase (days 1-14)?
- Mitosis of granulosa cells
- oestrogen production
- follicular fluid
- transformation of the primary oocyte into a secondary oocyte.
What happens during the early follicular phase regarding hormone regulation?
Oestrogen provides negative feedback, inhibiting GnRH, FSH, and LH release, leading to a drop in oestrogen.
What is the LH surge and when does it occur?
A surge in LH levels around days 13-14, triggered by rising oestrogen, leading to increased GnRH and LH release.
What is the result of the LH surge on the Graafian follicle?
Increases follicular fluid production and activates proteases, leading to ovulation and release of the secondary oocyte.
What does the secondary oocyte retain after ovulation?
Zona pellucida and corona radiata.
What is the corpus hemorrhagicum?
The structure formed from the Graafian follicle filled with blood post-ovulation.
What does the corpus luteum do?
Releases progesterone and inhibits further FSH release, supported by LH.
What occurs during the luteal phase (days 15-28)?
The corpus luteum is formed, primarily involving LH, and progesterone is released to maintain the uterine lining.
