Name: Male Reproductive Anatomy
Uploaded: 2019-07-19
Duration: 17 min 6 s
Description: Watch this video to learn about the anatomy of the male reproductive system and the components of the ejaculatory pathway and glands that generate semen.

Question

Show diagrammatically the stages of embryonic development from zygote upto implantation in human.

Accepted Answer

As a result of fertilization, the fertilized ovum transformed into a single cell, the zygote. Thus, a new individual starts life as a zygote. The zygote by repeated mitotic division produces many cells which in due time differentiate into different tissues and organs of the developing embryo. These repeated cell divisions of the zygote for the formation or development of embryo or fetus is called embryogenesis. The following phages of embryogenesis are required for the early development of an embryo before implantation in the uterine endometrium.

CLEAVAGE: The splitting or division of fertilized ovum (zygote) by series of mitotic cell divisions into a multitude of cells that become the building units of a future organism is called cleavage.

Process:
Cleavage starts at the beginning of embryological development. The process of cleavage is variously named segmentation or cellulation. The human ovum is alecithal (containing no yolk). It divides completely into two daughter cells called blastomeres by first cleavage division which passes from the median axis of the egg (median axis of the egg is the imaginary line joining the animal pole to legal pole). This type of cleavage is called holoblastic. The first cleavage is completed about 30 hours after fertilization. Now, the second division (which occurs more sooner in one blastomere than the other) occurs a right angle to the first, so that four blastomeres are formed. Then another in an orderly manner and in quick succession resulting blastomerers which gradually become smaller and smaller.

MORULA:
A solid ball of cells, which looks like a mulberry when the embryo reaches to 16 to 32 celled stage is called a morula.

Formation of Morula: The formation of morula is termed as morulation. Generally, the zona pellucida of zygote remains intact throughout the cleavage division, hence there is no increase in protoplasmic mass of the morular blastomeres. Therefore, the embryo does not show any appreciable increase in its size. The cells are compacted and of two types, outer slightly smaller peripheral cells with tight junctions than the inner mass of cells with gap junction.

BLASTULA: Aspherical mass consisting of a central cavity surrounded by a single layer of cells produced by the cleavage of the ovum is called a blastula.

Formation and structure of blastula (Blastulation):
The formation of blastula is termed as repeated cell divisions of the morula leads to the formation of thousands of segmented cells known as blastomeres. These blastomere cells are arranged themselves into the true epithelium of many cell thick. The epithelium formed by the blastomeres is blastoderm. Due to the migration of some blastomeres to the animal pole, a fluid-filled cavity is formed inside the mass of the cells. This cavity is called the blastocyst cavity. Once the blastocyst cavity is formed, the developing mass is now called a blastocyst. The size of the blastocyst remains the same as the size of the original zygote. A further arrangement of blastomeres results in the formation of two distinct structures - the inner cell mass and on outer superficial layers of cells. The outer superficial layer is called the trophoblast which forms the wall of the blastocyst. The inner cell mass of the blastocyst is destined to form an embryo.

Show diagrammatically the stages of embryonic development from zygote upto implantation in human.

Important Questions on Human Reproduction

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