Folliculogenesis Flashcards
What has to be achieved to reproduce?
- Differentiation into male or female
- Sexual maturation
- Production, storage + release of sufficient eggs + sperm
- Correct number of chromosomes in eggs + sperm (haploid)
- Eggs + sperm have to meet ie. gamete transport
- Creation of new individual with genes from both parents
- To nurture individual until capable of independent life
What are primordial germ cells?
Cells that become eggs or sperm
When and where are primordial germ cells (PGCs) first identifiable?
- ~ 3 weeks
- In yolk sac of developing foetus
What is the general pathway of the PGCs?
- First identifiable in yolk sac
- Undergo many cycles of mitosis
- Migrate to genital ridge in foetus
- Genital ridge -> gonad
- Further differentiation of PGC depending on development of gonad (ie ovary or testis)
How do PGCs become oocytes?
- Germ cells migrating + dividing by mitosis
- Germ cells become oogonia when in ovary
- Once mitosis stops, oogonia enter meiosis I + then arrest
- Remain arrested for decades -> these are primary oocytes
- (Upon ovulation they would enter meiosis II)
What are oogonia?
Oogonia are egg-precursors, diploid + multiply by mitosis
Why are mitotic divisions critical in forming eggs?
All the eggs that a women will ever have are made at this stage
Describe duplication of chromatids
- Chromosomes replicate during S-phase of cell cycle (interphase)
- Remain attached at centromere
- Each copy known as a chromatid -> 2 copies identical -> ‘sister chromatids’
- Exact copy of original chromosomes
What is a key difference/feature to be noted in oogenesis?
The unequal divsion of cytoplasm during cytokinesis
Where are primary oocytes found?
Packed into outer layer of the ovary : the cortex
Women are born with the follicle - describe the structure of the primordial follicle within the foetus
- Oocyte becomes surrounded by protective layers/cells
- In foetal ovary, surrounding cells condense around oocyte
- Cells differentiate into the granulosa cells
- The granulosa cells then secrete an acellular layer called basal lamina
- Whole structure is called primordial follicle
Define folliculogenesis
Defined as growth and development of follicles from the earliest “resting” stages as laid down in the foetus, through to ovulation.
Are follicles in the ovary growing? When do they grow?
Most of the follicles in the ovary are not growing - after puberty only a few grow each day
What happens to the structure of the follicle once it starts to grow?
- Granulosa cells multiply + ooctye secretes another protective acellular layer called zona pellucida… which stays attached after ovulation.
- Once growth of follicles has started, a second layer of cells then differentiate around basal lamina: the theca. Theca is vascularised.
- Follicle increases in diameter as granulosa cell divisions increase, gaps form between granulosa cells. Fluid fills these gaps (from theca) to form an antrum.
- Follicles with an antrum are known as antral or secondary follicles.
- Oocyte displaced to one side
What is the role of FSH within folliculogenesis?
The factors controlling inititation of follicle growth + early stages are largely unknown.
FSH drives most of folliculogenesis but early growth is independent of FSH. ie. driven by local factors
- > apparent in FSH-deficient patients or those w/ mutations of FSHr
- > also means even when FSH suppressed (eg on COCP), the follicles will still continue early growth but then die