Embryology

In the process of human reproduction, what happened during cleavage could be seen as the primary development. Cleavage is a process in which a single cell zygote (which is the cells that consist of ovum and sperm) continuously divides itself. Throughout the process, the main function of cleavage is to create an embryo through a process called mitosis.

There are two crucial reactions that take place during the development of an embryo. Acrosomal reaction is a reaction mediated mainly by calcium. During its process, significant changes in the sperm occur. This change is very important as the sperm transforms so that it would be able to penetrate through the ovum.  Another reaction called Cortical reaction occurs once the sperm has entered into the egg. Then, the egg releases calcium ions, and the cortical reaction is described as the sudden release of calcium as it fuses with the egg’s membrane.

During its initial stages, the zygotes form a spherical shape. It then undergoes a process called mitosis, which is a separation of the chromosomes in the nucleus in order to create two identical cells. As the cells go through the process of cleavage, the cells are now called blastula. In these cells, now named blastula, numerous molecules that deliver information. This differentiated information proceeds to the next stage, which is the development of the layers of the body. Gastulation is when the cells move in order to position themselves to form the different layers composed of cells. There are three main layers of gastulation, which includes...

Ectoderm: Ectoderm is the outermost layer. The tissues such as skin, hair, sweat glands, epithelium are all under this category.

Mesoderm: The mesoderm is the layer between the ectoderm and the endoderm. Its main function is to form structures that aid in the body movement and support, such as muscles, cartilage, bone, blood, and numerous other connective tissues.

Endoderm: The endoderm is the innermost layer that mostly forms tissues and organs of the digestive and respiratory systems. A few endocrine structures are also formed by the endoderm.

Blastula transforms into gastrula. During the stage of blastula, all cells are very similar in their shape and form, while as the embryo changes into gastrula, two distinct types are cells can be recognized. The two distinct cells can be characterized as outer layer, and the inner layer. The cells of the outer layer protect and react to external stimuli, while the inner cells focus more on the nutrition.  

Organogenesis is the final stage that the embryo goes through. During the organogenesis, the different layers of the embryo (the ectoderm, the endoderm, and the mesoderm) develop into different organs of the baby. The layers folds, splits, and condense in order to develop and differentiate the different organs.