4.3 Fertilisation and blastocyst development

Describe how pigs avoid retrograde semen transport.

Corkscrew penis enables intrauterine semen deposition

Describe how dogs avoid retrograde semen transport.

Mating position maintained creating high pressure

Which part of the spermatozoa produce energy?

Midpiece- filled with mitochondria

Describe how the sperm moves.

Axoneme microtubules sliding produce whiplash movement

Which part of the spermatozoa binds to the egg?

Equatorial segment

Describe the rapid transport phase of sperm.

Sperm reaches oviducts via fluid currents in uterus

Describe the sustained transport phase of sperm. (3)

• Capacitation- sperm fertilisation enabled in uterus (and ends in oviduct)

• Hyperactivation- sperm motility improved in oviduct

• Acrosome reaction

Describe the process of capacitation. (3)

• Removal of sperm head decapacitation factors to expose zona pellucida binding proteins

• Alteration of surface charge of CSM to attract sperm and egg

• Membrane fluidity increased to aid acrosome reaction

Describe how hyperactivation is done.

Increased intracellular Ca2+ induces elevation in cAMP

Cells outside oocyte zona pellucida

Cumulus cells

Describe the acrosome reaction. (5)

• Zona pellucida binding protein (ZP3) expsed during capacitation binds to zona pellucida

• Fusion of sperm plasma membrane and outer acrosomal membrane

• Acrosome releases hyaluronidase and acrosin to digest zona pellucida

• Equatorial segment exposed to fuse with oocyte

• Sperm moves into perivitelline space between zona pellucida and oocyte plasma membrane

How is polyspermy prevented during fertilisation?

Cortical granules block subsequent sperm from fusing with oocyte plasma membrane after sperm engulfed