DEP 4005 - Developmental Psychology Christine Ruva

"Miracle of Life"

Points Made About Prenatal Development

A - The germinal period or period of the zygote (fertilized egg) begins at the point of fertilization and lasts approximately 2 weeks. Mitosis quite rapidly after fertilization:

30 hours: 2 cell stage

40-60 hours: 4 cell stage

72 hours: 16 cell stage, zygote enters uterus

6 days: zygote sinks into uterine wall and implantation begins

8 days: placenta begins to develop

12-13 days: implantation

B - The embryonic period begins when the zygote is firmly implanted in the uterus and lasts from 2 weeks to the end of week 8. This period involves tremendous cell differentiation, so the embryo is especially vulnerable to teratogens. The spongy placenta "mediates" the metabolism of the mother and that of the embryo/fetus. It functions as a means of life support and as a protective layer filtering out some harmful substances like infections. It deals with nutrition, respiration, excretion, and endocrine exchange. The umbilical cord develops early in the embryonic period. It connects the embryo and the placenta. It contains one vein (carrying nutrients and oxygen and eventually hormones to the embryo) and two arteries (carrying off waste products and carbon dioxide). The embryo lies within the amniotic sac. The amnion is filled with a salt solution that bathes the body's cells and that contains substances necessary for the lungs to develop. The liquid also acts like a shock absorber and helps minimize temperature changes. The yolk sac is attached to the umbilical cord and helps create blood cells until the liver takes over this function.

C - Cartilage serves as a "mold" for skeletal development. As bone cells develop they actively invade and displace cartilage. The permanent skeleton begins to form around 8 weeks of age with the appearance of the first real bone cells. This marks the beginning of the fetal period which lasts until birth. This period is one of rapid growth.

D - The first reliable movements in human fetuses occur at around 10-11 weeks. These are reflex movements. Spontaneous movements begin around 12 weeks. Between 16 and 20 weeks the mother feels faint kicks for the first time.

The documentary we saw was originally broadcast on PBS on February 15, 1983. The majority of the photography was done by Swedish medical photographer Lennart Nilsson. Similar photographs may be found in his book A child is born.