Folliculogenesis Flashcards
Formation of Follicles
What has to be achieved to reproduce?
- Differentiation into male or female
- Sexual maturation
- Production, storage and release of sufficient supply of eggs and sperm
- Eggs and Sperm have to meet
- Creation of new embryo with genes from both parents
- To nurture individual
Where do cells that become genetic originate from?
Primordial Germ cells (PGC)
Where are Primordial germ cells (PGCs) first identified?
- First identified in the yolk sac of developing foetus (at 3rd week after conception)
- undergo many cycles of mitosis
- They migrate to the genital ridge in the foetus
- The genital ridge becomes the gonad
- Further differentiation of the PGC into male/female gametes
What happens if the PGCs enter the ovary?
- Germ cells become Oogonia when in the ovary
- Oogonia are the eggprecursors, diploid and multiply by mitosis
- Once mitosis stops and they enter into meiosis, known as primary oocytes
What happens when Germ cells convert to egg cells?
- All the eggs that a woman will ever have are made at this stage
- The mitotic divisions are therefore critical
- Once the Oogonia enter the first stage of meiosis, no more divisions occur and they become primary oocytes
- The primary oocytes remains in the first phase of meiosis until it is ovulated
Where are the primary oocytes packed?
Packed into the outer layer of the Ovary: The cortex
What is so special about the Oocyte?
- It is arguably the most important cell in the body and will remain in the vulnerable 1st meiotic phase for many years
- Therefore each one becomes surrounded by protective layers and cells
What happens to the surrounding cells around the oocyte?
In the foetal ovary
- Surrounding cells condense around the oocyte and differentiate into the Granulosa cells (GC)
- The Granulosa cells then secrete an Acellular layer called the basal lamina (BL)
- The whole structure is called the primordial follicle
Folliculogenesis: the growth of the follicle
What happens as the follicles start to grow?
- Most of the follicles in the ovary are not growing
- After puberty, a cohort of follicles initiate growth each day
- As the follicles start to grow, the Granulosa cells (GC) multiply and oocyte secretes another protective acellular layer called Zona pellucida (ZP)
- Once growth of the follicles has started a second layer of cells then differentiate around the basal lamina (BL): the theca, which is vascularised
What factors control the follicle growth?
- Factors controlling initiation of growth and the early stages are largely unknown
- But Granulosa cells multiply & oocyte enlarges
- FSH drives most of folliculogenesis but early growth is independent of FSH
What happens as the follicles start to grow?
- As the follicle starts to grow, it increases in diameter and Granulosa cells divisions increase
- But gaps begin to form in the Granulosa cell layers
- These gaps consist of fluid filled spaces which form an antrum & are filled with follicular fluid
What are the 2 phases of follicle growth?
Labelled by presence or absence of antrum
What are follicles with an antrum known as?
As Antral or secondary follicles
What are the 6 different follicle classifications?
- Preantral or Primary Follicles
- Antral or secondary Follicle
- Preovulatory or Graafian follicle
