Fertilisation Flashcards
State the 6 stages of fertilisation
- Sperm capacitation
- Penetration of corona radiate
- Attachment of zone pellucida
- Activation: acrosome reaction
- Sperm entry
- Blocks to polyspermy
State the two processes required for fertilisation to occur
Capacitation and Activation
Describe capacitation
Involves the removal of glycoproteins and sterol groups from the plasma membrane of the sperm. Secretions from the uterus wall and uterine tubes destabilise the plasma membrane surrounding acrosome. Sperm become hyperactive so flagella move more rapidly and their heads move laterally through the corona radiate and come into contact with the zone pellucida which expresses ZP3 protein that binds to head of sperm and triggers acrosome reaction.
Where does capacitation occur?
Post-ejaculation within female genital tract
Describe the acrosomal reaction
Enzymatic contents of the acrosome are released and they digest the zona pellucida so the sperm can enter the perivitelline space and reach the plasma membrane of the secondary oocyte membrane. Fusion of the sperm and oocyte membrane then occurs
Describe ‘fast block’
Oocyte membrane depolarises to block sperm fusing with it
Describe ‘slow block’
It is stimulated by the depolarisation and a wave of intra-cellular calcium is released causing small cortical granules beneath the oocyte membrane to release their contents to make ZP3 inactive so zone pellucida is impermeable
State the 2 reactions slow block interacts with
Cortical reaction and zone reaction
What is the result of the cortical reaction
Results in the formation of impenetrable oocyte membrane
What is the result of the zone reaction?
Prevents sperm binding to zona pellucida through structural changes.
Describe the process of oocyte maturation
- Germ cells become primordial follicles
- Produces formation of the primary and secondary follicles
- FSH levels increase to induce maturation of follicle
- Then there is a mature tertiary follicle (AKA Graafian follicle)
What are follicles?
A group of cells that surround the developing egg at different stages of development
What is a Graafian follicle
A mature tertiary follicle. The oocyte has undergone its first meiotic division and is still 2n chromosomes