Fertilisation

Question 1

State the 6 stages of fertilisation

Answer 1

1. Sperm capacitation
2. Penetration of corona radiate
3. Attachment of zone pellucida
4. Activation: acrosome reaction
5. Sperm entry
6. Blocks to polyspermy

Question 2

State the two processes required for fertilisation to occur

Answer 2

Capacitation and Activation

Question 3

Describe capacitation

Answer 3

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.

Question 4

Where does capacitation occur?

Answer 4

Post-ejaculation within female genital tract

Question 5

Describe the acrosomal reaction

Answer 5

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

Question 6

Describe ‘fast block’

Answer 6

Oocyte membrane depolarises to block sperm fusing with it

Question 7

Describe ‘slow block’

Answer 7

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

Question 8

State the 2 reactions slow block interacts with

Answer 8

Cortical reaction and zone reaction

Question 9

What is the result of the cortical reaction

Answer 9

Results in the formation of impenetrable oocyte membrane

Question 10

What is the result of the zone reaction?

Answer 10

Prevents sperm binding to zona pellucida through structural changes.

Question 11

Describe the process of oocyte maturation

Answer 11

1. Germ cells become primordial follicles
2. Produces formation of the primary and secondary follicles
3. FSH levels increase to induce maturation of follicle
4. Then there is a mature tertiary follicle (AKA Graafian follicle)

Question 12

What are follicles?

Answer 12

A group of cells that surround the developing egg at different stages of development

Question 13

What is a Graafian follicle

Answer 13

A mature tertiary follicle. The oocyte has undergone its first meiotic division and is still 2n chromosomes