Folliculogenesis Flashcards
When are primordial germ cells first identifiable in the yolk sac?
3 weeks after conception
What do cells that will become oocytes or sperm cells originate from?
Primordial germ cells
What are the steps in development of primordial germ cells?
Lots of mitosis
Migration to the genital ridge
Genital ridge becomes the gonad
What happens if primordial germ cells enter the ovary?
Known as oocytes
When do oogonia become primary oocytes?
When they stop dividing by mitosis and enter the first stage of meiosis
What is the outer layer of the ovary called and what is it made up of?
The cortex - primary oocytes
In the foetal ovary, what do the cells surrounding the oocyte do and what are they called?
Condense and differentiate into granulosa cells
What do granulosa cells secrete?
The basal layer
What is the whole structure (granulosa cells, oocyte and basal lamina) called?
Primordial follicle
What stage of meiosis are oocytes arrested in?
Metaphase I
What happens to the oocytes at ovulation?
Primary oocyte splits into a secondary oocyte and the first polar body
What’s the difference between a first polar body and a secondary oocyte?
More cytoplasm in the secondary oocyte
What is folliculogenesis?
The growth and development of follicles from the earliest resting stages in the foetus through to ovulation
How often does a cohort of follicles initiate growth?
Every day
What happens as follicles grow?
Granulosa cells multiply and the oocyte secretes another protective acellular layer called the zona pellucida
What happens to the follicle once follicular growth has started?
The second layer of cells differentiate around the basal lamina (the theca) which is then vascularised
Is early follicular growth FSH- dependant?
No
How do we know that early follicular growth is FSH-independant?
Know this bc it still happens in FSH deficient patients or those with FSHR mutations
What are the two main phases of follicle growth?
Pre-antral and antral
What are antrums?
Follicular fluid-filled spaces
As the antrum grows, what do the cells surrounding the oocyte differentiate into?
Cumulus cells
What do pre-ovulatory follicles contain?
Cumulus oophorus complex
Granulosa cells
Vascularised theca laying adjacent to the basal lamina
What is the follicular fluid made up of?
Plasma exudate and secretory products of the oocytes and granulosa cells
What happens as the follicular fluid volume and antrum expands?
The oocyte is displaced to one side
What is follicle initiation?
When a cohort of early follicles leave the resting pool and start growing continuously
What is it called if follicle initiation happens at the same time as FSH release in the menstrual cycle?
Follicle recruitment
Why is the vascularisation of the theca important?
It allows the follicle to be open to external influences and release steroids into circulation
What do theca cells produce?
Androgens
Where are FSH receptors found?
ONLY granulosa cells
Where are LH receptors found?
ONLY theca cells
What does FSH do in granulosa cells?
Drives aromatase to catalyse androstenedione -> estradiol
What does LH drive in theca cells?
Cholesterol -> androgens
Where do the testosterone and androstenedione produced in theca cells travel to and what do they do there?
The granulosa cells, converted into estrone and estradiol
What is the only time you will find LH receptors on granulosa cells and why?
In the dominant follicle because it needs to drive progesterone production
What is the zona pellucida?
A thick glycoprotein shell on the follicle that stops more than one sperm fertilising it
