1. Stages of Prenatal Development
Ovum is the largest cell of the body (size=.) Sperm weigns 1/30,000 as
much. Stages of prenatal development are influenced by both nature
Conception is also known as fertilization (the combination of an 23
chromosomes from egg with 23 chromsomes from sperm).
Once every 28 days (half way through a woman's menstrual cycle), an
egg is released by either the right or left ovary into the fallopian tube.
Over the next 24 hours, the egg can be fertilized by a sperm (which can
stay in the woman for 2-3 days).
Only one sperm penetrates the egg --> zygote
b. The Period of the zygote (conception to 2nd week)
Zygote multiplies rapidly as it continues its 4 day journey (10 cm)
Zygote becomes from solid mass of cells-->hollow sphere-->cells begin
to specialize (some inner cells will become embryo, some will support
Implantation takes ~1 week. Zygote settles into the blood-enriched
lining of the uterus and will remain attached throughout pregnancy
Period of zygote = ~2 weeks -->first missed period-->sign of pregnancy c. The Period of the embryo (3rd week- 8th week)
Begins when implantation is complete--> 8th week
All major internal and external structures form during this period
The time when growing embryo is most vulnerable to threats