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Begins...
... with the start of pregnancy and continues until the birth of the child. Prenatal development consists of three distinct successive periods: preimplantation period, embryonic period, and fetal period. the preimplantation period and the embryonic period makes up the first trimester of the pregnancy, and the fetal period constitues the last two trimesters. -
Preimplantation Period: week 1
At the beginning of the week, the union of ovum and sperm forms a fertilized egg, or the zygote. Meiosis occurs and joins the sperm's chromosomes with the ovum's. Zygote undergoes mitosis. Because of ongoing process of mitosis and secretion of fluid by the cells within the morula, the zygote now becomes blastocyst. By the end of the week, blastocyst stops traveling and undergoes implantation and is embedded in the endometrium in the uterus. -
Embryonic Period: week 2
The implanted blastocyst grows by increased proliferation, with differentiation also occurring resulting in changes in cellular morphogenesis. The increased number of embryonic cells creates the embryonic cell layers, or germ layers, within the blastocyst. A bilaminar embryonic disc developed from the blastocyst, having a superior (epiblast) and inferior (hypoblast) layer. -
Embryonic Period: week 3
-Primitive streak forms within the bilaminar disc
-Some cells migrate from epiblast to hypoblast layer
-Migratory cells become mesoderm, a CT
-The bilaminar disc thickened into trilaminar disc:
Epiblast->ectoderm: skim epidermis, CNS, and other structures
Migratory cells->mesoderm: connective tissue, cartilage, bone, etc.
Hypoblast->endoderm: respiratory epithelium and cells of glands
-Neural crest cells is developed from neuroectoderm. -
Embryonic Period: week 3 cont'd
-The neural crest cells (NCCs) are developed from neuroectoderm.
-These cells migrate from the crests of the neural folds and then disperse within the mesenchyme. Mesenchyme is involved in the development of many face and neck structures.
-NCCs essential in the formation of most oral and dental tissue, except for the enamel and certain types of cementum, as well as the development of the face and neck. -
Embryonic Period: week 4
The trilaminar disc undergoes anterior and lateral folding which puts them in their place for further development. This folding results from extensive proliferation of the ectoderm and differentiation of the basic tissue. After the folding, digestive tract is developed and divided into three groups: foregut, midgut, and hindgut. Also, the face and neck begin to develop, the primitive eyes, ears nose, oral cavity, and jaw areas. -
Embryonic Period: week 5
The development of of face and neck continues to develop:
-Mandibular arch and lower face formation
-Frontonasal process and upper face formation
-Maxillary process and midface formation -
Embryonic Period: week 6
The development of face and neck continues to develop with the addition of upper and lower lip formation at the start of week 6. -
Embryonic Period: week 7
The development of face and neck continues to develop. The upper lip is completed during the end of this week. -
Embryonic Period: week 8
The embryo is recognizable by this week, which is the end of embryonic period. -
Fetal Period: third to ninth month
The maturation of existing structure occurring as the embryo enlarges to become a fetus. Process involves maturation and further proliferation, differentiation, and morphogenesis. Though the embryo has been breathing since the third week or prenatal development, the the end of the fourth month, the fetal heartbeat and fetal movements are also present. -
Birth
