Your Growing Embryo...Fetus...Baby !
How amazing is it that two tiny cells, each with only 1/2 the chromosomes required to create a human being, meet in the dark, quiet interior of the woman's fallopian tube where fertilization begins the journey from embryo to fully formed and mature fetus, ready for life outside the womb..I am greatly appreciative to the
Endowment for Human Development (EHD) for their wonderful and informative website! The EHD is a nonprofit organization
dedicated to improving health science education and public health. EHD equips all persons: individuals, educators, clinicians, and governments to help
everyone to appreciate, apply, and communicate the science of health & human development.
Fertilization: Egg & Sperm Meet ~ Fertilization begins when a single spermatozoon (sperm) penetrates the zona
pellucida, which surrounds the oocyte (egg). This event triggers a reaction
called the zona reaction, which dramatically alters the outer membrane
and prevents the entry of any additional spermatozoa into the oocyte.
The Early Blastocyst
The cells lining the perimeter of the embryo will help form the placenta
and are called trophoblast cells.
These cells bring water, minerals,
and amino acids from the nutrient-rich environment outside the embryo
into the blastocyst cavity where they can reach the cells of the inner
cell mass.
Implantation Well UnderwayImplanation occurs early in pregnancy in which the embryo adheres to the wall of uterus. At this stage of prenatal development, the embryo is a blastocyst. It is by this adhesion that the fetus receives the oxygen and the nutrients from the mother to be able to grow. Implantation occurs approximately 9 days after ovulation, ranging between 6 to 12 days.
The Three-Week Embryo
The brain emerges about 2½ weeks following fertilization. By three weeks, the major sections of the brain are identifiable.
Label Key:
1. midbrain
2. forebrain
3. hindbrain
4. somites
The Four-Week EmbryoThrough
a complex series of folds, the disc-like embryo now has a head and a
tail, with buds that will grow into limbs. The beginnings of a spinal
column 
and muscles are apparent. The embryo is about 4 to 5 millimeters
long -- a bit less than 1/4 inch.
At 7.5 weeks, the embryo's:
- eyes move forward on the face and eyelids begin to form
- palate is nearing completion and the tongue begins to form
- gastrointestinal tract separates from the genitourinary tract
- essential organs, all, have begun to form; interestingly enough, the embryo goes through 3 sets of kidneys during this time!
MORE to COME!