Oogenesis and the Ovarian Cycle Flashcards
When does maturation of oocytes begin?
Before birth
Where do germ cells arise from?
The yolk sac
What happens after germ cells have arisen from the yolk sac of the female?
They colonise the gondal cortex and differentiate into oogonia
What happens once germ cells have differentiated into oogonia?
They proliferate rapidly by mitosis, and some enter meisois
What is oogonias entry into meisois 1 stimulated by?
Mesonephric cells
What are mesonephric cells?
Flattened epithelial cells, also called Follicular Cells
What happens to the oogonia in meisosis 1?
They arrest in the diplotene stage (a resting stage) of prophase 1
What causes oogonia to arrest in the diplotene stage of prophase 1?
Due to Oocyte Maturation Inhibitor
What secretes Oocyte Maturation Inhibitor?
Follicular cells
What are the oogonias that are arrested in the diplotene stage now known as?
Primary oocytes
When is the maximum number of germ cells reached?
Mid-gestation
What happens to the number of germ cells at mid-gestation?
Cell death begins, and many oogonia and primary oocytes degenerate
What is the process of degeneration of oogenia and primary oocytes known as?
Atresia
What has happened to the oogonia by the 7th month of gestation?
The majority of oogonia have degenerated
How many primary oogonia survive by the 7th month of gestation?
˜2 million
What has happened all surviving primary oocytes by the 7th month of gestation?
They have entered meisosis I, and are surrounded by a flat layer of epithelial cells- follicular cells
What are the primary oocytes surrounded by follicular cells now called?
Primordial follicles
How long to the primordial follicles remain in meiosis I?
At least until puberty
What happens to most oocytes during childhood?
Most undergo atresia
How many oocytes remain by puberty?
˜40,000
What is the clinical relevance of a woman having all the oocytes she will ever have at birth?
Some may remain arrested for 50 years before further development, increasing the chance of cell damage and thus accounting for the increased risk of foetal chromosomal abnormalities in pregnancies of older women
What happens to oocytes from puberty onwards?
˜15-20 oocytes start to mature each month
What stages do oocytes go through when maturing?
- Pre-antral
- Antral
- Pre-ovulatory
What happens in the pre-antral stage of maturation?
- Primary oocyte grows dramatically, but does not re-start meiosis
- Flat follicular cells become cuboidal Granulosa cells, and proliferate, producing stratified epithelium
What do Granulosa cells do in the pre-antral stage?
Secrete glycoprotein
What is the purpose of the glycoprotein secreted by the Granulosa cells in the pre-antral stage?
It surrounds the oocyte with a Zona Pellicuida
What do surrounding connective tissue (stroma) cells form in the pre-antral stage?
A Theca Folliculi
What does the Theca Follucli consist of?
- An inner Theca Interna
- An outer Theca Externa
What are the characteristics of the Theca Interna?
- Vascular
- Endocrine
What is the Theca Externa?
A fibrous capsule
What do Theca and Granulosa cells collaborate to do?
Secrete oestrogens