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Chapter-05 Development of Human Embryo

BOOK TITLE: Essentials of Anatomy for Dental Students

Author
1. Selvakumari TL
ISBN
9789352703548
DOI
10.5005/jp/books/14250_6
Edition
1/e
Publishing Year
2018
Pages
6
Author Affiliations
1. Sri Venkateswara Dental College and Hospital, Thalambur, Chennai, Tamil Nadu, India
Chapter keywords
Human embryo, gestation, morula, blastocyst, blastomeres, trophoblast cells, inner cell mass, bilaminar germ disk, endoderm, ectoderm, mesoderm

Abstract

Human sperm and ovum are haploid having 23 single chromosomes each and they unite together to form a human embryo which is diploid having 46 single chromosomes. In the first week of gestation the embryo multiplies by mitotic division and forms a morula. Further, these totipotent cells multiply and differentiate. A cavity is formed between the cells known as the blastocyst. The blastomeres arrange themselves in two groups: trophoblast cells which form the placenta and the inner cell mass which becomes the embryo proper. By the second week of gestation the bilaminar germ disk is formed. The inner cell mass differentiates into two germ layers: cuboidal cell layer is the endoderm and the columnar cell layer is the ectoderm. At one end the cuboidal cells transform into columnar cells and form a prochordal plate and on the other end the columnar cells transform into cuboidal cells and form the primitive streak. During the third week of gestation trilaminar germ disk is formed comprising of three layers: ectoderm, endoderm and mesoderm. Gastrulation is the process of formation of primitive streak and the third germ cell layer. Somites start appearing on the 20th day of gestation.

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