Folliculogenesis Flashcards
What has to be achieved in order for reproduction to occur?
- Differentiation into male or female
- Sexual maturation
- Production, storage and release of sufficient supply of
eggs and sperm - Correct no. of chromosomes in eggs & sperm
- Eggs and 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 germ cells?
Cells that will become eggs or sperm are called primordial germ cells (PGC)
When do PGCs first become identifiable?
PGCs first identifiable in the yolk sac of the developing foetus at 3 weeks after conception
How do PGCs differentiate?
- Undergo many cycles of mitosis
- They migrate to the genital ridge in the foetus
- The genital ridge becomes the gonad (testes/ovaries)
- Further differentiation of the PGC depend on the
development of the gonad i.e. ovary or testis
How do PGCs differentiate into oocytes?
If PGCs enter the ovary they become oocytes
Germ cells become oogonia when in the ovary
Oogonia are egg-precursors, diploid and multiply by mitosis
Once mitosis stops and they enter into meiosis, known as primary oocytes
Surrounded by layer of GC – now known as primordial follicle
Why are the mitotic divisions during PGC differentiation so significant?
All the eggs that a woman will ever have are made at this stage
The mitotic divisions are therefore critical
What happens once to oogonia enters meiosis?
Once the oogonia enter the 1st stage of meiosis no more division occurs and they become primary oocytes
How long do primary oocytes remain in meiosis?
The primary oocytes remains in the first phase of meiosis until it is ovulated (or dies) ~maybe for 52 years!
During which phase of the cell cycle do chromosomes replicate?
Chromosomes replicate during S-phase of the cell cycle
Copies remain attached at the centromere
What are chromatids?
As long as the replicate copies remain attached, each copy known as a chromatid → the 2 copies are identical to each other → “sister” chromatids
What are the 4 stages of mitosis?
Prophase; Metaphase, Anaphase & Telophase
In which ways are meiosis and mitosis similar?
Meiosis and mitosis begin the same way. Both are preceded by the replication of chromosomes.
outline one way meiosis differs from mitosis
Meiosis has 2 divisions instead of one
Describe what occurs during the first division in meiosis
Chromosome no. reduced, as 2 homologues of chromosome pair (each replicated into two chromatids attached by a centromere) are separated into 2 cells - each cell has one member of each homologous pair of chromosomes
What happens during the second meiotic division?
Replicated chromatids of each chromosome are separated
Meiosis produces four haploid cells.
The orderly movements of chromosomes during meiosis ensure each haploid gamete produced contains one member of each homologous pair of chromosomes
What are the stages of meiosis?
Each of the 2 meiotic divisions has four stages similar to those in mitosis: prophase, metaphase, anaphase, and telophase (I and II)
How does oogenesis differ from regular meiosis
The difference in oogenesis is the unequal division of cytoplasm during cytokinesis.
Where are primary oocytes located?
Primary oocytes are packed into the outer layer of the ovary: the cortex
Why are the primary oocytes so heavily surrounded by cells?
Oocytes arguably the most important cell in the body and will be in the vulnerable 1st meiotic phase for many years
Therefore each one becomes surrounded by protective layers and protective cells
What protects the oocyte when in the foetal ovary?
In the foetal ovary, the surrounding cells condense around the oocyte and differentiate into granulosa cells
The granulosa cells then secrete an acellular layer called the basal lamina
What is the primordial follicle composed of?
consists of an oocyte surrounded by a single layer of flat, supporting granulosa cells
What is the clinical definition of folliculogenesis?
Defined as the growth and development of follicles from the earliest “resting” stages as laid down in the foetus, through to ovulation
How many follicles are undergoing growth in the ovaries?
Most of the follicles in the ovary are not growing – after puberty a cohort grow each day
What effect does follicle growth have on the granulosa cells?
As the follicles start to grow, the granulosa cells multiply and the oocyte secretes another protective acellular layer called the zona pellucida which stays attached after ovulation
