Blastula vs Gastrula
In all sexually reproducing coelomates, there are four main stages of embryogenesis, namely; fertilization, cleavage, gastrulation, and organogenesis. Fertilization is the fusion of haploid male and female gametes to form a diploid zygote. Zygote is the new cell, which is also known as fertilized ovum. In the process of cleavage, the zygote rapidly divides into many cells, without increasing the overall size of it and ends up with a structure called blastula. In mammals, it is called blastocyst. Then the continuous development of blastula finally ends with a structure called gastrula. The formation of gastrula is called gastrulation. The three germ layers of gastrula interact in various ways to form organs, hence called organogenesis. Since, blastula and gastrula occur separately as different structures in different phases, there are some differences can be observed between both structures.
Blastula
Blastula represents the first important stage after the fertilization and plays an important role in the development of organisms. It is a hollow, spherical, one celled thick structure formed by the process called blastulation. Both holoblastic and meroblastic cleavages give rise to blastula. The cavity inside the blastula is called blastocoel, and its outer single cell layer is called blastoderm.
Gastrula
The continuous development of blastula finally results the gastrula. The conversion process of the blastula into gastrula is called ‘gastrulation’. Gastrulation is followed by the organogenesis. Gastrula is composed of three primary germ layers, which eventually give rise to organs in the late embryo. The primary germ layers are ectoderm, mesoderm, and endoderm. Ectoderm is the outermost layer of gastrula, which differentiates into skin, brain, spinal cord, and nerves of embryo. Mesoderm is the middle layer, which forms muscles, connective tissues, reproductive organs, cartilage, bones, and dermis of skin and dentine of teeth. Endoderm is the innermost layer of the embryo and basically differentiates into primitive gut.
What is the difference between Blastula and Gastrula?
• During the embryogenesis process, formation of blastula is followed by gastrula.
• Formation of blastula is called blastulation, whereas the formation of gastrula is called gastrulation.
• Rapid mitotic divisions of zygote results blastula while slow mitotic divisions of blastula results gastrula.
• During the formation of blastula, cells do not move, but during the formation of gastrula, cell masses move by morphogenetic movements.
• Three primary germ layers are present in gastrula unlike in the blastula.
• Blastula is often called a pre-embryo, whereas gastrula is referred to as a mature embryo.
• Gastrula has more cells than blastula.
• Gastrula has differentiated cells, while blastula has undifferentiated cells.