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Embryology study of prenatal development Prenatal development consists of three distinct periods the pre-implantation period, the embryonic period, and the fetal period What periods make up the first trimester of pregnanacy the pre-implantaiton period and the embryonic period What period comprises the last two trimesters the fetal period It is important for dental professionals to understand what in prenatal development to understand the major events of prenatal development to understand better the development of the structures of face, neck, and oral tissue and underlying relationships among these structures Primordium earliest indication of a part or an organ during prenatal development, all structures have this Know teratogens involved in congenital malformations drugs(tetracycline, ethanol, lithium), chemical(methylmercury, polychlorinated biphenyls), infections (rubella virus, herpes simplex virus, human immunodeficiency virus, syphilis microbe), radiation(high levels of ionizing type) Preimplantation period of prenatal development period of the unattached conceptus, takes place during the first week Zygote union of ovum and sperm forms a fertilized egg During fertilization, the final stages of what occurs meiosis, diploid chromosomes, half from ovum, half from sperm After fertilization, zygote under goes mitosis, individual cell division(cleavage) Morula after intial cleavage, solid ball of cells Blastocyte zygote becomes a vesicle, also known as blastula, after ongoing process of mitosis, many cells When does the blastocyte stop traveling end of the first week, then undergoes implantation, embedded in prepared endometrium Trophoblast layer after 7 days of cleavage, blastocyst consists of a layer of peripheral cells Embryoblast small inner mass of embryonic cells Trophoblast gives rise to important prenatal support tissues Embryoblast layer gives rise to to embryo during next prenatal period Down syndrome trisomy 21, extra 21 chromosome after meiotic division, at risk of periodontal disease and fewer and abnormally shaped teeth, arched palate, poor use of tongue muscles Cell becomes zygote after how many hours: 12-24 Cell divides into two cells after how many hours 30 hours Cell divides into 4 cells after how many hours 40-50 hrs Cell divides into 8 cells after how many hours 60 hrs Cell divides into 12-16 cells after how many days 4 days Blastocyte at which day 5 days Implantation occurs how many days 6 days Embryonic period of prenatal development extends from beginning of second week to end of eight week What physiological process occur at embryonic period induction, proliferation, differentiation, morphogenesis, and maturation The physiological process cause the structure of implanted blastocyst to become an embryo, also allow teeth to develop in embryo Induction action of one group of cells on another that leads to the establishment of the developmental pathway in the responding tissue, many problems can occur from failure of induction Proliferation controlled levels of cellular growth present during most of embryological development Interstitial occurs deep within a tissue or organ, soft tissue are usually this Appositional which a tissue enlarges its size by the addition of layers on the outside of a structure, hard tissues usually this Differentiation change occurs in the embryonic cells, which are identical genetrically but become quite distinct structuraly and functionally, give cells specialized fucntions Beginning of all major organs, tissues and organ systems form during differentiation Cytodifferentiation development of different cell types Histodifferentiation development of different tissues within a structure Moprhodifferentiaton development of differeing structure or morphology, for eeach organ or system Morphogenesis process of development of specific tissue structure or shape, migration of embryonic cells and inductive interactions of those cells Maturation tissues and organs begins during embryological period and continues during the later fetal period, recognizably human at end of embryonic period at end of 8th week Second week of prenatal development embryonic period implanted blastocyst grows by increased proliferation of embryonic cells, cellular morphogenesis and differentiation Embryonic cell layers germ layers within blastocyte Bilaminar embryoic disc developed from blastocyst, appears as flattened, circular plate of bilayered cells Hypoblat layer inferior layer, small cuboid cells Epiblast layer superior to hypoblast, high columnar cells Bilaminar disc is suspended between what two fluid filled cavities amniotic cavity, yolk sac Amniotic cavity faces epiblast layer Yolk sac faces the hypoblast layer, nourishment for embryonic disc Placent prenatal organ that joins pregnant woman and developing embryo, develops from interactions of trophoblast layer and endometrial tissues Third week development withing embryonic period, primitive streak from within balaminar disc What causes disc to have bilateral symmetry primitive streak Mesenchyme an embryonic connective tissue, cells from epiblast layer mirgrate toward hypoblast to form this Mesoderm connective tissues creates a new embryonic layer called this Epiblast considered ectoderm Hypoblast considered endoderm Ectoderm and endoderm are part of trilaminar disc Ectoderm gives rise epidermis of skin, nervous system and other structures Mesoderm gives rise muscles coats, connective tissues, vessels supplying tissue and organs Endoderm gives rise to epithelial linings of respiratory passages and digestive tract, including some glandular organs cells