Embryology – New World Encyclopedia – Info:Main Page – New …

From New World Encyclopedia

Embryology is the branch of developmental biology that studies embryos and their development. The field of developmental biology encompasses the overall study of the process by which organisms grow and develop, including cell growth, cellular differentiation, and, "morphogenesis," which is the process that gives rise to tissues, organs, and anatomy. Embryology, a subfield of developmental biology, is the study of organisms between the one-cell stage (generally, the zygote) and the end of the embryonic stage, which is not necessarily the beginning of free living.

Embryology was originally a more descriptive science until the twentieth century. Embryology and developmental biology today deal with the various steps necessary for the correct and complete formation of the body of a living organism.

The wonder by which a single, fertilized egg differentiates into diverse cells, tissues, organs, and systems of a fully formed organismthe heart, lungs, brain, arms, endocrine system, muscles, and bones of a human, for instanceremains a mystery that embryologists attempt to unravel.

Embryology is the classic study of morphological changes within the embryo. Aristotle is said to be the first person to undertake a study in embryology. Aristotle observed the ontogeny of chicken embryos by breaking open eggs at various time intervals during incubation.

In the 1950s, with the discovery of the structure of DNA by Watson and Crick, and the rapidly increasing knowledge in molecular biology, developmental biology emerged as a field of study interested in the role that genes play in development. In other words, developmental biologists wanted to know which genes are responsible for each morphological change that occurs in development. Perhaps even more importantly, developmental biologists sought to explain how the various cell types of a multicellular organism arise from a single fertilized cell, the egg.

Development of an embryo can be divided into several stages. The first stage is fertilization, in which the sperm penetrates the egg. The nuclei of the sperm and egg then fuse to form a diploid zygote (with paired chromosomes). Cleavage follows, in which the single cell composing the embryo undergoes mitosis (cell division), resulting in many cells called blastomeres. Each blastomere has the exact same genome (set of DNA) as the zygote. These blastomeres come to compose a solid ball of cells called a morula. The final event of cleavage involves the formation of a blastula, or a hollow ball of blastomeres containing a blastocoel, or fluid-filled cavity.

Gastrulation is the stage in which the blastomeres partition themselves into three distinct germ layers: the ectoderm, mesoderm, and endoderm. The ectoderm is the outermost layer and will eventually develop to form the skin and nervous system. The endoderm is the innermost layer and will eventually develop to form the lining of the gut and internal organs. The mesoderm is the middle layer, which eventually forms the muscles, bones, and heart.

After the forming of the gastrula (the multi-layered structure formed during gastrulation), the cells begin to differentiate, or undergo physical and chemical changes that will determine their individual identities (as muscle cells, kidney cells, etc.). Growth is the last stage, in which cells divide and proliferate, eventually composing all the major organs of the body.

One of the significant questions that early developmental biologists sought to answer was how cell individuation occurs. Almost every cell in the body contains the exact same DNA as every other cell, as they all are derived from the initial zygotic cell. So how is it that some cells become cardiac cells and others become skin cells?

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Embryology - New World Encyclopedia - Info:Main Page - New ...