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What are oogonia?
Developing germ cells which divide by mitosis.
What are primary oocytes?
Larger germ cells that are ready to undergo meiosis
What are granulosa (follicular) cells?
Cells with form a barrier around an oocyte, protecting and feeding it
What is a primordial follicle?
An ooctye surrounded by a layer of follicular cells
How many primordial follicles does one have at birth?
What is atresia?
Process of degrading and dying primordial follicles
What is menarche?
- 40 000 remaining primordial follicles
- beginning of sexual maturity
What is menopause?
0 eggs remaining
What are the four hormones involved in endocrine control of the menstrual cycle?
- Peptide hormones: follicle-stimulating hormone, luteinizing hormone
- Steroid hormones: estrogen and progesterone
What are the two divisions of the menstrual cycle?
Ovarian cycle and uterine cycle
Describe the structure of the ovary.
- Surface- simple cuboidal epithelium continuous with lining of the peritoneal cavity
- Tunica albuginea- white appearing ECM devoid of blood vessels and cells
- Cortex- outer layer of ovary containing ovarian follicles
- Medulla- inner layer in which blood vessels enter and leave
What changes occur during days 1-14 of the ovarian cycle?
- Follicular phase (development of follicle under the influence of FSH)
- Primordial follicle to primary follicle- cells change from squamous to cuboidal epithelium
- Zona pellucida forms between the oocyte and the follicular cells
- Granulosa cells divide into several layers and begin to produce estrogen
- Surrounding CT differentiates into 2 layers; theca interna and theca externa
- With increasing FSH levels, the primary follicle becomes a secondary follicle and then a Graafian follicle
What is the zona pellucida?
- ECM between granulosa cells and oocytes
- contains extensions from both the oocyte and granulosa cells- holds them together
What are the theca interna cells?
- differentiated fibroblasts
- produce androstenediaone, a precursor to estrogen
What are theca externa cells?
- differentiated fibroblasts
- have contractile functions which aid in the expulsion of the egg
How is estrogen produced in the ovary?
The granulosa cells pick up the androstendione produced by the theca interna cells and convert it into estrogen. They then secrete it in large amounts.
What is a secondary follicle?
Follicle containing 'lakes' full of estrogen
What is a Graafian follicle?
Intracellular spaces merge to form one large space aka the antrum. The antrum contains estrogen and hyaluronic acid. Formation of the antrum pushes the oocyte off to one side where it sits on a group of granulosa cells calles the cumulus oophorus.
What is the cumulus oophorus?
A group of granulosa cells supporting the oocyte in a Graafian follicle.
What is the corona radiata?
The layers of granulosa cells actually surrounding the oocyte in a Graafian follicle. No different from the cumulus oophorus.
What is the function of hyaluronic acid in a follicle?
- Exists in the antrum of a Graafian follicle
- It is viscous and helps to protect the oocyte.
What changes occur during ovulation?
- The high estrogen level has negative feedback on FSH and positive feedback on LH produced the LH surge.
- The LH surge influences the follicle to finish the 1st meiotic division and enter the 2nd division, stopping at metaphase (primary oocyte to secondary oocyte).
- The secondary oocyte doesn't progress any further unless fertilization occurs.
- Ovulation occurs under the influence of LH and the contractile function of the theca externa.
What changes occur during days 14-28 of the ovarian cycle?
- Luteal phase
- High levels of LH influence the production of the corpus luteum which is made up of theca lutein cells (produve mainly estrogen) and granulosa lutein cells (produce mainly progesterone) as well as an external corpus luteum.
- It eventually degrades into the corpus albicans (remaining ECM).
- If fertilization doesn't occur, LH turns off and FSH is produced again.
What happens if fertilization occurs?
The egg will produce human chorionic gonadotrophin (HCG) which takes over the function of LH, continuing the stimulation of production of estrogen and progesterone. It continues this role for about 3 months until the placenta has formed.
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