Embryology

The word embryology is derived from Greek word ‘embryon’ meaning embryo. The branch of science that deals with development of an embryo right from the fertilization stage of ovum till the fetus stage is referred as embryology. Once the embryo cleaves the cells get divided and it becomes blastula or as hollow ball where it develops it into a hole or pores at one of the end. In case of blastula animals, the blastula gets developed in two ways either by dividing the whole animal kingdom in to two such halves. In case of blastula the blastopore that is first pore acts as mouth of an animal and are referred as protosome. The first pore behaves like anus then it is referred as deuterostome. The protosomes shall include most of the invertebrate animals for instance worms, mollusks and insects. However deuterosomes shall include vertebrates such as humans. In due course of time, blastula gets converted into more differentiated structure and is referred as gastrula.

The gastrula along with blastopore shall soon develop into three distinct layers of cell which are referred as germ layers where in the body organs and tissues get developed in to following types of layers.

• Endoderm: Inner most layer is endoderm  shall give rise to lungs, bladder and digestive organs
• Mesoderm: Middle layer is mesoderm shall give to muscles, blood system and skeleton
• Ectoderm: Outer most layer is ectoderm shall give to skin and nervous system

In case of humans, embryo refers to dividing cells from the zygote in the nucleus till the eight week after sexual conception. Fetus develops after the eight week. The embryo shall appear in many of the developmental stages. The reason behind this similarity is that evolutionary history share same components. Similar species are called as homologous structures which has similar function and mechanism.

Questions:

• What is embryology?
• Brief out history of embryology.
• What is ontogeny?