Growth, Development, and Function of the Ovarian Follicle Flashcards
The neurovascular components are concentrated in which portion of the Ovary?
Medulla
List the different stages that are involved in the development of Ovarian Follicles. (7)
- Resting Primordial Follicle
- Growing Preantral (Primary/Secondary) Follicle
- Growing Antral (Tertiary) Follicle
- Dominant (preovulatory, graafian) Follicle
- Dominant Follicle within the Periovulatory Period
- Corpus Luteum (of menstruation or of pregnancy)
- Atretic Follicles (degenerate before coming to maturity)
Describe the structure of the Primordial Follicle.
- This is the Ovarian Reserve of Follicles
- Consists of Primary OOCYTE with a SINGLE layer of pregranulosa cells
- Granulosa Cells will provide nutrients to developing oocytes
Which hormone is important for making sure that there are not TOO many Primordial Follicles are developed.
Anti-Mullerian Hormone
What happens to the Primordial Follicles when you smoke?
It will deplete the Ovarian Reserve!
How many Primordial Follicles are going to go through ovulation?
About 450
What is happening with the Gamete in the Primordial Follicle Stage?
Oocyte is arrested in PROPHASE I
Describe the Endocrine function of the Primordial Follicle.
- NO Endocrine Function
- Will release Paracrine Factors
What is the Pleitrophy of the Primary Oocyte?
4N (Diplotene)
Describe the Structure of the Growing Preantral Follicle.
- Cuboidal Granulosa Cells (Primary Follicle)
- Stratified Epithelium around Oocyte (Secondary Follicle)
- Secondary Follicle is going to release paracrine factors that induce differentiation of Thecal Cells
- Secondary Follicle will secrete angiogenic factors that will bring vascular supply to the developing follicle
What is happening with the Gamete in the Growing Preantral Follicle Stage?
- Oocyte begins to grow
- Secretes ZP1, ZP2, and ZP3 that will form the zona pellucida
- Granulosa cells and the oocyte project cellular extensions through the zona pellucida to maintain gap junction contacts
Which type of receptors are Thecal and Granulosa Cells going to express?
Thecal Cells: LH Receptors
Granulosa Cells: FSH Receptors
Describe the Endocrine function of the Preantral Follicle.
DO NOT produce ovarian hormones at this stage
What is the major product of the Thecal Cells? Why?
Androstenedione
Thecal cells do not express high levels of 17B-Hydroxysteroid Dehydrogenase
Describe the structures associated with the Growing Antral Follicles.
- Fluid spaces appear between cells and flow into the antrum
- Mural and Cumulus Granulosa Cells appear
Differentiate between Mural and Cumulus Granulosa Cells.
Mural Granulosa Cells: Form the outer wall of the follicle, Basal Layer is stuck to basal lamina, REMAIN in ovary to differentiate into the CORPUS LUTEUM (will be able to produce progesterone and estrogen)
Cumulus Granulosa Cells (Corona Radiata): Inner cells that surround the Oocyte, Maintains Gap Junctions with Oocyte, RELEASED with the Oocyte during OVULATION (Helpful for the fimbrated end of the oviduct to grab and move the oocyte into the uterine tubes!)
Which hormone is required for normal growth of the Early Antral Follicles and the selection of the Dominant follicle?
FSH
Describe what is happening with the Gamete in the Growing Antral Follicles.
- Oocyte is going to synthesize cell cycle components (CDK1 and Cyclin B)
- Larger Antral Follicles are going to gain meiotic competence but still maintain meiotic arrest until the midcycle LH surge
Describe the Endocrine function in the Growing Antral Follicles.
- Thecal cells are producing High levels of Androstenedione and Testosterone (Much less T)
- FSH stimulates proliferation of granulosa cells and induces expression of AROMATASE
- Androgens are converted into Estradiol-17B by the MURAL Granulosa Cells
- MURAL Granulosa cells are also going to be responsible for producing inhibin B
- LOW levels of estrogen and inhibin will exert negative feedback on FSH secretion
What is the major determinant when deciding the Dominant Follicle?
The Follicle with the MOST FSH Receptors!
What happening with the Gamete in the Dominant Follicle?
- Still arrested in meiosis I (prophase I)
- Stalk of Cumulus cells attaching them to Granulosa Cells becomes thin
Describe the Endocrine function of the Dominant Follicle.
- Thecal Cells are expressing LH receptors and produce estrogens
- Granulosa Cells are expressing FSH receptors
- FSH is going to up-regulate aromatase gene expression and activity
- FSH induces the expression of LH receptors in the mural granulosa cells during the 2nd half of the Follicular Phase
- MURAL granulosa cells that become responsive to both FSH and LH which allows the maintenance of high levels of AROMATASE with declining FSH levels
- LH receptors will also make sure that the granulosa cells will respond to the LH surge!
Define the Periovulatory Period
- Time from onset of LH Surge to Ovulation
- 32-36 Hours
What happens at the end of the Periovulatory Period?
Antral Cavity become continuous with the Peritoneal Cavity!
What is the function of GDF9?
Stimulates Cumulus cells to secrete hyaluronic acid and other EC matrix components that make it easier to capture the oocyte in the OVIDUCT and easier form sperm to locate
Describe what is happening with the Gamete during the Periovulatory Period.
- LH surge induces the release from arrest and completion of meiosis I
- Now stuck in METAPHASE II of meiosis II
Describe the Endocrine Function during the Periovulatory Period.
Estradiol-17B and Over-Production of Progesterone are the two main steroids that are being produce.
Explain how the Corpus Luteum is formed.
- Granulosa Cells become Granulosa Lutein Cells which will fill up with Cholesterol Esters
- These cells will eventually collapse and fill in the ANTRAL cavity
How long does the Corpus Luteum typically Last?
14 days until it is rescued by hCG
Which type of peptide hormones are going to be produced by Granulosa Lutein Cells?
Inhibin A
When the follicle is developing, what structure marks the gonadotropin dependency?
Development of an antrum!
