In Vivo Fertilization: Definition & Process

Instructor: Adrianne Baron

Adrianne has a master's degree in cancer biology and has taught high school and college biology.

We are going to get a working definition of in vivo fertilization and discuss the different players as well as the process of in vivo fertilization. We will discuss natural in vivo fertilization as well as assisted in vivo fertilization.


Ricardo and Lea have made the decision that it is time for them to add a new addition to their family. They are planning to have a baby. Both Ricardo and Lea know that reproduction, or the creation of an offspring, can result from having sex, but they are not sure about the details of the full process. They want to be sure they know everything there is to know about producing and taking care of a newborn baby. Their first step is to learn how the process of reproduction starts. They begin to read about fertilization, which is the joining of male and female gamete cells. The male gamete is a sperm while the female gamete is called an ovum.

In Vivo Fertilization

Their reading goes on to explain the two options for fertilization. The joining of sperm and ovum naturally takes place in the fallopian tubes, which are the narrow tubes that lead from the ovaries to the uterus in the female. When fertilization takes place in its natural location inside of the female body, it is called in vivo fertilization, whereas fertilization that takes place outside of the female body is called in vitro fertilization. Ricardo and Lea decide to focus on in vivo fertilization since they do not have any reason to think that they will need reproductive help requiring in vitro fertilization.

Natural Process

They learn that the process of in vivo fertilization is relatively simple even though it does not occur every time they have sex. Lea's ovary will ovulate, meaning that it releases an ovum from the ovary to enter the fallopian tube. The ovum will remain in the part of the fallopian tube that is closest to the ovary for about 24 to 48 hours. During the process of sex, Ricardo will release anywhere from 100 to 300 million sperm in an attempt to fertilize Lea's ovum.

Ricardo's sperm will swim the journey from the vagina where they enter, across the cervix of the uterus, through the body of the uterus to Lea's fallopian tube. Most of the sperm released will not be able to make the entire journey, so the number of sperm at this point is in the hundreds. The sperm that make it to the ovum in the fallopian tube will attempt to penetrate the outer covering of the ovum called the zona pellucida.

The sperm use their heads to penetrate the zona pellucida. No, Ricardo's sperm are not going to think their way into the ovum, but they are going to use the proteins in their heads to break through the zona pellucida. As soon as one of the sperm is able to break through, a chemical charge changes on the surface of the zona pellucida, which prevents any other sperm from getting into the ovum. The sperm continues inside of the ovum until it reaches the nucleus, which is the part of the cell where the genetic material is stored. The sperm's head will dissolve, releasing its nucleus. The nucleus of the ovum and sperm will fuse together to make one fertilized cell.

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