Zygote

Welcome to this lesson today. You are going to be learning about the process that occurs from the time a zygote develops to the time it is implanted in the uterus. Specifically, you will learn about:

1. The Process Overview
2. Beginning Stage
3. Middle Stage
4. Final Stage

1. The Process Overview

A zygote is a fertilized egg that's made up of one cell and is an individual's first cell. The zygote will divide repeatedly in order to eventually develop into a human being. A zygote, which is a fertilized egg, has to undergo various cell divisions before it can implant within the endometrium of the uterus. Fertilization usually occurs in the ova duct, so the zygote will start to undergo cell divisions as it moves through the ova duct on its way to the endometrium. Implantation generally will occur six to seven days after conception.

• Zygote
• The fertilized egg which is the first cell of an individual.

2. Beginning Stage

The process starts with the zygote which is one cell and eventually it will divide into two cells with a cleavage furrow. Cleavage is basically just that process of starting with one cell, and building up this ball of cells that will eventually become a human. Cellular materials called polar bodies will eventually disintegrate and leave just the dividing zygote to travel down the ova duct. The cell has divided by the process of cleavage and we now have two cells.

3. Middle Stage

Each of the cells are then going to divide, as well ending up with a ball of four cells. Each cell is dividing by the process of mitosis and each new cell that has formed is called a blastomere. A blastomere is each new cell that's formed during the process of cleavage. Each blastomere is going to end up with a little of the original zygote's cytoplasm. The bit of cytoplasm that ends up within the new blastomeres are going to determine the developmental path of that cell. In summation we have gone from a single zygote and after two cleavages/divisions we now have four cells.

The new cells are then going to divide and eventually we'll end up with a ball of 16 cells called a morula. Eventually, as the morula moves towards the uterus it will develop into a blastocyst.

4. Final Stage

As the morula reaches the uterus around day five, it starts to develop a fluid-filled cavity and develops into a blastocyst; the blastocyst consists of different layers. The trophoblast is the surface layer of cells while the inner cell mass and develop into an embryo. Then the blastocyst eventually will, as it moves towards the uterus, implant into the uterus. The embryo will develop then from the inner cell mass of the blastocyst.

• Blastocyst
• After the morula forms it will implant on the endometrium of the uterus; the blastocyst contains an inner of layers of cells that become the embryo while the outer layer of cells form the placenta.
• Inner Cell Mass
• A layer of the blastocyst which will develop into an embryo.
• Embryo
• A stage of development of an individual formed from the inner cell mass of a blastocyst after it has implanted in the uterus.

This lesson has been an overview of the beginning, middle, and final stages of how a zygote will eventually implant into the endometrium of a uterus.

Keep up the learning and have a great day!