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Preimplantation Period
This period takes place at the beginning of the first week. Sperm fertilizes the ovum and they unite to create a zygote after the process of meiosis. -
Embryonic Period
This period extends for the beginning of the second week to the end of the eighth week. Most of the development happens within the 4th week.
During this time, the developmental processes such as Induction, Proliferation, Differentiation, Morphogenesis, and Maturation, which all further the development of an embryo. -
Second Week
During the second week, Increased proliferation of the embryonic cells causes the implanted blastocyst to grow and the bilaminar embryonic disc is developed. In this stage, the placenta is formed. -
Third Week
The primitive streak forms within the bilaminar disc which cases the disc to have a right and left half Some cells from the epiblast layer move toward the hypoblast layer only in the area of the primitive streak which create layers The three layers(Mesoderm, Endoderm, and Ectoderm) called the trilaminar embryonic disc, which gives the rise of specific tissue. CNS begins to form within the ectoderm and things such as bones, blood, connective tissue, muscle start to form within the endoderm. -
Fourth Week
Embryonic folding resulting from extensive proliferation of the ectoderm and differentiation of basic tissues during this period allows for proper development The future digestive tract is created and separated into three regions, the foregut, midgut, and hindgut The foregut forms the primitive throat, the midgut and the hindgut form the rest of the mature pharynx. The face and neck begin to develop, with primitive eyes, nose, oral cavity, and jaw areas. -
Fifth Week
During this week, the brain, heart, and spinal cord are being formed. The umbilical cord replaces the yolk sac and the heart begins to beat. -
Sixth Week
The upper lip is formed when the maxillary process fuses together as well as the nasal processes and the rest of the face. -
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Fetal Period
This period follows the embryonic period and continues until the 9th month of pregnancy. This process involves the maturation of the existing developments, individual tissues and organs, and also further proliferates, differentiates, and morphogenesis.
