Folliculogenesis Flashcards
What has to be achieved to reproduce?
Our embryo has to differentiate into male and female which then go on to mature sexually.
After sexual maturation, we have to produce, storage and release sex cells. Of those sex cell, we need to produce the right number of chromosome within it.
Said sperm and eggs have to meet so we need to facilitate the transport of the gametes from the male to female reproductive tract so fertilisation can occur.
What is the common ancestry of sperm and egg cells?
Primordial germ cells.
Can be identified as early as three weeks after conception.
How does primordial germ cells become eggs?
Once a PGC reaches the ovaries it becomes oogonia. Oogonia are oocyte precursors.
- they are still in a diploid state
- Once mitosis stops they undergo meiosis and rest at anaphase.
- They remain in this until it dies or it gets fertilised, they are known as primary oocytes after anaphase
How many eggs does a female infant have at birth?
At the peak, you have about 7,000,000 oocytes but this is before birth and at about 16-24 weeks. After this, the number of oocytes just drops to about 1,000,000 after birth. The reason of apoptotic oocytes are unknown.
How long can a primary oocyte remain in its state?
Once an oogonia enters the 1st stage of meiosis no more division occurs and they become primary oocytes.
Primary oocytes can remain in this state up to 52 years.
3 Reason for dead oocytes
Defective oocytes
Follicles are not formed
Defective chromosome rearrangement within the oocyte
Where can you find the primary oocytes?
In the Cortex (outer layer) of the ovary.
They are immature and remain in meiotic arrest for many years.
How are oocytes protected? (Layers of the organelle)
In foetal ovary, the surrounding cells of the oocytes condense and form a layer of granulosa cells which secret an acellular layer - called basal lamina.
What is a primordial follicle?
It is an oocyte surrounded by granulosa cells and then another layer of Acellular layer of basal lamina outside of that.
What is folliculogenesis?
It is the growth and development follicles from the earliest stages as it is laid down in the foetus, through to ovulation.
When does follicular growth starts?
It starts after the activation of HPG axis which is when puberty starts.
You then get a cohort of follicles growing every day.
How does follicle grow?
Follicle growth involves the multiplication of granulosa cells and the growth of the oocyte.
-the growth of oocyte involves replicating mRNA, protein synthesis and just laying down cellular stuff to prepare for early development if successively ovulated.
What does the oocyte secret as it grows during follicular growth?
And does it detract after ovulation?
As the oocyte grow it secret a cellular layer called the zona pellucida.
It is a mark of oocyte growth and it remains attached after ovulation.
Which cells are layer down and differentiated around the basal lamina after follicular growth?
And what is the growing follicle made up of?
The theca is the layer of cell that surrounds the basal lamina which surrounds the granulosa cells which surrounds the zona pellucida which protects the oocyte.
What drives follicle growth?
How do we observe this?
FSH generates folliculogenesis,
We don’t know what initiates it’s or drives the early stages.
We can observe effects of FSH on folliculogenesis via FSH-deficient patient or those with mutations of FSHr
