Development Of The Human Zygote Essay -- essays research papers fc

Development of the Human Zygote     Hundreds of thousands of time a year a single-celled zygote, smallerthan a grain of sand, transforms into an amazingly complex network of cells, anewborn infant. Through cellular speciality and maturation, this process iscompleted with precision time and time again, b argonly very rarely a mistake in the"blueprint" of growth and festering does occur. Following is a description ofhow the pathways of this intricate web are followed and the mistakes whichhappen when they are not.     The impressive process of differentiation changes a single-cell into acomplicated system of cells as distinct as bold and bone. Although immaturedevelopment takes approximately nine months, the greatest amount of cellulardifferentiation takes place during the first eight weeks of pregnancy. Thisperiod is called embryogenesis.     During the first week later on fertilization, which takes place in theFallopian tube, the embryo starts to cleave once every 24 hours (Fig.1). Until the eight or sixteen cell stage, the individual cells, or blastomeres,are thought to have the potential to form any part of the foetus (Leese, Conaghan,Martin, and Hardy, April 1993). As the blastomeres continue to divide, a solidball of cells develops to form the morula (Fig. 1). The accrual of fluidinside the morula, transforms it into a hollow sphere called a blastula, whichimplants itself into the midland lining of the uterus, the endometrium (Fig. 1).The privileged mass of the blastula will produce the embryo, period the outer layer ofcells will form the trophoblast, which eventually will ply nourishment tothe ovum (Pritchard, MacDonald, and Gant, 1985).Figure 1Implantation process and development duringembryogenesis (Pritchard, MacDonald andGant, 1985)     During the second week of development, gastrulation, the process bywhich the germ layers are formed, begins to occu r. The inner cell mass, nowcalled the embryonic disk, differentiates into a thick plate of exoderm and anunderlying layer of endoderm. This cellular multiplication in the embryonicdisc marks the beginning of a thickening in the midline that is called the yokelish streak. Cells spread out laterally from the primiti... ...e anormal infant. When something does go wrong, the embryo or fetus willunfortunately have some slip of defect. The amazing accuracy with which asingle cell can work something as complex as a newborn infant is a truleyincredible featWorks CitedBaker, David A. "Danger of Varicella-Zoster Virus Infection." ContemporaryOB/GYN April 1990 52.Carlson, Bruce M. Pattens Foundations of fertilized egglogy. McGraw-Hill Inc. 1981.Cunningham, MacDonald, and Gant. Williams Obstetrics, Supplement no. 10. 18thed, Prentice-Hall, Inc. Februay/March 1991 2,3."Folic Acid for the Prevetion of Recurrent nervous Tube Defect." Medicine March1993.Harrison, Ross G. Organiz ation and Develpment of the Embryo. Yale UniversityPress. 1969.Leese, Conaghan, Martin, and Hardy. "Early Human Embryo Metabolism." BioEssays vol. 15, No. 4 April 1993 259.Pritchard, MacDonald, and Gant. Williams Obstetrics. 17th ed, Prentice-Hall,Inc. 1985 139-142, 800.Pritchard, MacDonald, and Gant. Williams Obstetrics, Supplement no. 13. 17thed, Prentice-Hall, Inc. July/gilded 1987 2."Teratology." ACOG Technical Bulletin February 1985.