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Preimplantation Period
This stage occurs during the first week and is where conception and fertilization occur. -
Embryonic Period
Is the second period of prenatal development. Extends from the beginning of the second week to the end of the eighth week. Induction, proliferation, differentiation, morphogenesis, and maturation take place. -
Second Week
increased proliferation of the embryonic cells. An embryonic cell layer and bilaminar embryonic disc is developed. The placenta is developed during this week. -
Third Week
The primitive streak forms within the bilaminar disc. Some cells of epiblast layer migrate toward the hypoblast layer. The three layers Endoderm, Mesoderm, and Ectoderm are formed. In the ectoderm the central nervous system begins to form. In the endoderm bones, blood, muscles and connective tissue begin to form. -
Fourth Week
The trilaminar embryonic disc undergoes anterior and lateral embryonic folding. The future digestive tract is being formed and is separated into three regions: the foregut, midgut, and hindgut. The face and neck begin to develop. The primitive eyes, ears, nose, oral cavity, and jaw areas. -
Fifth Week
The umbilical cord replaces the yolk sac. The brain, heart, and spinal cord are developed during this week. The heart also begins to beat. -
Sixth Week
The maxillary process fuses together, along with the rest of the face. The upper lip is also formed. -
Fetal Period
occurs the ninth week (third month) and goes until the ninth month. The process involves the physiologic process of maturation, proliferation, differentiation, and morphogenesis. By the end of the fourth month, the fetal heartbeat and fetal movements are also present.
