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Preimplantation Period
This phase takes place over the first week prior to conception. Sperm fertilizes the egg when joined with the ovum. -
Embryonic Period
This process extends from the second week to the end of the eighth week. Physiological processes referred to as "patterning" occur and are key to further development. The Physiological processes are induction, proliferation, differentiation, morphogenesis and maturation. -
Second Week
The implanted blastocyst grows by increased proliferation of the embryonic cells. DIfferentiation also occurs which changes cellular morphogenesis. Embryonic cell layers are created from the increased number of embryonic cells. The bilaminar embryonic disc is essentially the embryo as development progresses. -
Third Week
At the start of the third week, primitive streaks form in the bilaminar disc. These streaks cause the disk to have a right and a left side forming the mesoderm layer. Some cells from the epiblast layer start to move specifically to the hypoblast layer inside of the primitive streak. After the formation of the mesoderm, the resulting trilaminar embryonic disc consists of the ectoderm, mesoderm and endoderm. -
Fourth Week
The trilaminar embryonic disc undergoes anterior cephalic and lateral embryonic folding. This places tissues in their designated spots. The folding is a result of extensive proliferation of the ectoderm and differentiation of basic tissue. The future digestive tract is separated into three major regions known as foregut, midgut and hindgut. The neck and face develop with the eyes, ears, nose, oral cavity and jaw region. -
Fifth Week
The formation of the brain, heart and spinal cord begin to form. The umbilical cord is replaced with a yolk resulting in heartbeat. -
Sixth Week
The maxillary process fuses creating the upper lip, the nasal process, and the remaining facial structures. -
Fetal Period
This is the final period of prenatal development. This is the start of the third month. This process consists of the physiological process of maturation of individual tissue types and organs as well as more in depth proliferation and morphogenesis.
