Comprehensive Fertilization and Early Embryonic Development in Human Biology

What process allows sperm to gain the ability to fertilize the egg?

Capacitation

What reaction allows sperm to penetrate the zona pellucida?

Acrosome reaction

What prevents multiple sperm from fertilizing the egg?

Cortical reaction (block to polyspermy)

Approximately how many sperm reach the fallopian tube?

A few hundred

At what stage are all cells totipotent?

Morula stage

What are the two main cell types in the blastocyst?

Trophoblast and inner cell mass

What is the function of trophoblast cells?

Implantation, enzyme secretion, hCG secretion, placenta formation

When does implantation begin?

~Day 6 post-fertilization

What hormone maintains the corpus luteum in early pregnancy?

hCG

What is hCG similar to?

LH

What does the corpus luteum secrete?

Progesterone and estrogen

When does the placenta take over hormone production?

~10 weeks

What happens to hCG levels after ~6 weeks?

Decrease

What structures form the placenta?

Trophoblast (fetal) + endometrium (maternal)

Does maternal and fetal blood mix in the placenta?

No

What is exchanged in the placenta?

Nutrients, O2, CO2, wastes

What do umbilical arteries carry?

Deoxygenated blood

What does the umbilical vein carry?

Oxygenated blood

When are embryonic genes activated?

8-cell stage

What process forms the 3 germ layers?

Gastrulation

What are the three germ layers?

Endoderm, mesoderm, ectoderm

Which layer forms the nervous system?

Ectoderm

What hormone decreases maternal insulin sensitivity?

Placental lactogen

What is a major function of progesterone during pregnancy?

Maintain uterine lining and prevent contractions

What hormone stimulates uterine contractions strongly?

Oxytocin

What type of feedback occurs during labor contractions?

Positive feedback

What triggers milk production after birth?

Drop in estrogen and progesterone

What is an ectopic pregnancy?

Implantation outside uterus (usually fallopian tube)

What type of twins come from two separate eggs?

Dizygotic (fraternal)

What type of twins come from one fertilized egg splitting?

Monozygotic (identical)