Folliculogenesis In The Human Ovary
What is Folliculogenesis?
Folliculogenesis is a process by which a follicle grow through several stages and development .This follicles are located in the cortex of ovary and it contain oocyte.
The development of follicles is more complex ,involves many integration of receiving signals from several organ system.
The process of folliculogenesis will come to an end by two forms ,one by atresia and other will get matured.
Stages Of Folliculogenesis
Different stages of Follicles
- Primordial Follicle
- Primary Follicle
- Secondary Follicle
- Early tertiary Follicle
- Late tertiary Follicle
- Graafian Follicle
- Corpus luteum
It is the first stage of follicular development and it has a layer of pre-granulosa cells.
Primodial follicles starts to produce in the third month of gestation and about 4to5 million of primordial follicles are formed.
Many of the follicle dies during fifth month of gestation due to atresia.
It has the immature oocyte in it.
Its count will decreases ,it has 25,000-1.5million during puberty and get decreased by 1000 in menopause.
Its average size will be 0.03-0.05mm in diameter.
In this stage the follicle has the flat cells (i.e. pre- granulosa cells)that surrounded by the oocyte, now become cubic(die) shaped granulosa cells.
Along with the follicles, the oocyte also get develop in their size.
In this stage the paracrine pathway is activated (i.e. communication between the follicle and oocyte.).
Size of the follicles in this stage will be 0.1mm in diameter.
Primary follicle starts to develop the receptors of FSH, but it is gonadotropin independent till the antral stage.
Zona pellucida which is composed of glycoprotein will starts to form.
In this stage the granulosa cells surrounds the oocyte in several stages from 6-7 layers .
Following the granulosa cells ,the presumptive theca cells are formed.
The basal lamina undergo differentiation and becomes theca interna ,capillary net and theca externa.
In this stage the oocyte is surrounded by zona pellucida and layer of granulosa cells.
EARLY TERTIARY FOLLICLE:
This stage is also known as pre-antral follicle stage.
The granulosa cells and theca cells will continue to develop by several stages.
In this stage, the granulosa cell will acquire the FSH receptor. Thus, from this stage the follicular development will become gonadotropin dependent.
In this stage the size of follicles will be around 0.2-5mm under five classes I,II,III,IV,V of division.
In this stage the antrum starts to form.
LATE TERTIARY FOLLICLE:
This stage is also known as antral follicle stage.
Follicular cavity has the follicular fluids knowns as antrum, due to this antral fluid the oocyte is located by the sides of the follicle.
The development of the follicle is now dependent on FSH and LH.
In this stage , the selection and dominance stage of the follicle is established.
The follicle which has the ability to complete their developmental stages is known as dominant follicle.
The size of follicles is about 10mm-20mm from classes VI-VIII of division.
Graafian follicle is also known as pre-ovulatory follicle is a fully developed follicle and oocyte, then the ovulation process will occur.
The granulosa cells surrounds the oocyte forms the cumulus oophorous or cumulus.
When the gonadotropin attain the peak ,the cumulus oophorus will produce the hyaluronic acid.
Due to this acid, the cumulus will increase in their size and get a mucus consistency. This process is known as mucification of the cumulus and it is important for ovulation process.
After the ovulation(i.e. the oocyte released from the ovary), the follicles which left over in ovary will become corpus luteum.
It useful to produce estrogen and enhance the amount of progesterone, which helps in ovulation.
In the pregnancy woman the corpus luteum will present upto fourth month.
If the pregnancy have not occurred it will get degenerated.
In the whole perspective, the whole folliculogenesis from primordial follicle to preovulatory follicle comes under the ootidogenesis of oogenesis.
Until the preovulatory stage, the follicle has a oocyte that is arrested in prophase I until the puberty.
At the late preovulatory stage, the oocyte continuous the meiosis and secondary oocyte get arrested in metaphase II till the fertilization occur.
Classification of Folliculogenesis:
BASED ON DEVELOPMENT:
BASED ON HORMONES:
Gonadotropin independent phase
Late gonadotropin dependent phase