Ch 29- Development System

Question 1

Polyspermy

Answer 1

fertilization by two or more sperm which would produce a doomed
fertilized egg

Question 2

Two mechanisms to prevent polyspermy

Answer 2

Fast block: binding of the sperm to the egg opens Na+ channels in egg membrane
* Inflow of Na+ depolarizes membrane and inhibits the attachment of any more sperm

Slow block: Cortical granules sit under the egg’s surface.

Sperm entry causes a calcium (Ca²⁺) surge.

Calcium triggers cortical granules to release contents.

The released material swells with water.

This blocks other sperm and forms a protective barrier.

Question 3

Dizygotic twins

Answer 3

Two eggs are ovulated and both are fertilized by separate
sperm forming two zygotes
* No more or less genetically similar than any other sibling
-own placentas

Question 4

Monozygotic twins

Answer 4

• One egg is fertilized (one zygote) but embryoblast divides into
  two up to 14 days after fertilization
• Genetically identical (or nearly so), of the same sex, and very
  similar in appearance

Question 5

Postnatal Develop

Answer 5

-look at diagram last slide
Baby has to start living on its own right after birth.

Breathing: Cutting the cord raises CO₂ → baby takes first breath.

Heart:

Hole between heart chambers (foramen ovale) closes.

Blood vessel shortcuts (ductus arteriosus & umbilical vein) close and turn into ligaments

Question 6

fetal stage

Answer 6

-blastocyte until end of week 2
-embryo week 3-8
-fetus- rest of terms