Difference Between Morula and Blastula

Morula vs Blastula
 

The difference between morula and blastula is to do with the different developmental stages of the egg. Major developmental stages of egg after the fertilization are zygote, morula, blastula, and embryo. Fertilization is an important biological process resulting in the first embryonic stage, the zygote. Formation of morula and blastula are considered as the early embryonic developmental stages of animals. After the formation of the zygote, it transforms to the next stage, called the blastula. This transformation process is governed by a unique embryological biological process called cleavage. During the cleavage, series of mitotic divisions take place in zygote to produce daughter cells, which are genetically similar to their parent cell. These new daughter cells are now called blastomeres. With the time, morula differentiates into blastula, which has a higher cell number and different structure. In this article, differences between morula and blastula will be outlined.

What is Morula?

Morula is a ball-like mass of cells formed by the cleavage of the zygote. Morula usually consists of 16 – 32 cells. The first cleavage in human zygote occurs in the fallopian tube, about 30 hours after fertilization. Second and third cleavage take place about 60 hours and 72 hours after fertilization respectively. Cleavage increases the number of cells, but not result in growth. Thus, morula has the same size as the zygote. As a result of subsequent cleavage division, morula forms into a centrally located inner cell mass and a surrounding layer, the outer cell mass. During the embryonic development, the inner cell mass forms the tissues of the embryo while the outer cell mass gives rise the trophoblast, which lately develops into the placenta. Morula reaches the uterus within 4-6 days after fertilization.

Difference Between Morula and Blastula

What is Blastula?

Once the morula is formed, the trophoblast cells in the center of the morula start to secrete fluid into the center of the morula forming a fluid-filled space, called blastocoel. Now the embryo resembles a hollow ball-like structure known as the blastula. Blastocoel is surrounded by single cell layer known as trophoblast or trophectoderm. Blastula is present in all vertebrates during their embryonic development. However, in mammalian species, blastula consists of an inner cell mass on the inner surface on one side of the blastula, whereas no such inner cell mass is found in non-mammalian species. The face of blastocyst, where inner cell mass is attached is known as embryonic pole or animal pole, whereas the opposite side is called abembryonic pole. During the development of blastula, zona pellucida starts to disintegrate, which enhances the growth of the embryo.

What is the difference between Morula and Blastula?

• During the embryonic development, zygote transforms to morula and then morula transforms to blastula.

• The cells inside the morula are larger than the cells that form blastula.

• The number of cells in blastula is larger than that in morula.

• Morula is a solid structure with no fluid-filled cavity inside. But blastula is a hollow structure, due to the presence of fluid-filled space called blastocoel.

• Trophoblast cells are present in blastula unlike in morula.

• Unlike in blastula, morula consists of an inner and outer cell masses.

• Duration of the formation of morula is lower than the formation of the blastula .

 

Images Courtesy:

  1. Development & implantation of the embryo by  Sunshineconnelly (CC BY 3.0)