What is Human Fertilization? - Process, Definition & Symptoms

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Lesson Transcript
Instructor: Kelly Robson

Kelly has taught High School Science and Applied Communications. She holds an Education Specialist Degree in Ed. Leadership.

Human fertilization is a complicated process that results in a fertilized egg. The fertilized egg will mature in the womb of its mother until birth. This lesson will go over the process, basic definition, and some symptoms of human fertilization.


Simply put, the definition of human fertilization is the union or joining of the egg and the sperm, resulting in a fertilized egg, otherwise known as a zygote. But the process of human fertilization is very complicated and comprised of many steps and components necessary to achieve the ultimate result of human life. Read on to learn how such small things work together to make a fertilized egg.


The process of human fertilization is a complicated one, but the egg and sperm will unite in the long run. Although technical in nature, you could also look at it as a journey to find the perfect match. The egg will sit waiting for one sperm out of up to 150 million that begin the race, and it will merge with that sperm to create human life. While the egg waits, the sperm race and compete to be the first to penetrate the egg. When the one sperm and egg finally meet, electricity fills the air. Seriously, electric signals are released. Although the details may not be so romantic, remember that it is the journey that counts.

Human fertilization begins with a woman's menstrual cycle. This cycle prepares a woman's body for fertilization. About half way through this cycle, the woman's body is ready to begin the process of human fertilization. It is at this point that an egg cell is released, or ovulated, into the Fallopian tube. Inside this Fallopian tube, fertilization will take place.

Human Egg Cell Diagram
Human egg cell

During intercourse, a man can ejaculate, or release semen into a women's vagina. There are up to 150 million sperm in the semen in a single ejaculation. The sperm travel to the Fallopian tube to meet the egg; however, the sperm have some big challenges ahead to complete this journey. For instance, the sperm have to complete this journey within 12-48 hours of the egg being ovulated, or else they will die.

The sperm racing to be the first and only sperm to penetrate the membrane of the egg.
Human Sperm Cell

About 85% of the sperm are not properly structured for travel. This leaves only about 15% of the sperm to complete the journey to the egg. The remaining sperm will follow chemical signals given by the vagina and cervix, the opening of the uterus. The chemical signals will guide the sperm through the cervical mucus and up the lining of the uterus. The uterus is also known as the womb and is where the baby will develop after fertilization.

Only about 1,000 sperm are left. After the sperm make it through the uterus, they face the challenge of picking the correct Fallopian tube. There are two Fallopian tubes, and only one contains the egg. The sperm that choose the correct Fallopian tube will finally reach the egg.

This process, from ejaculation to the remaining sperm reaching the egg, takes about 20 minutes. At this point, there are only a few dozen sperm left that actually make it to the egg. The remaining sperm begin to surround the egg, and they race to be the first and only sperm to actually fertilize the egg.

The head of each sperm begins to release an enzyme to breakdown the egg membrane, the outer layer of the egg. Once the first sperm penetrates through the membrane of the egg, the egg will begin to emit an electric signal. See, I told you electricity fills the air when two become one! The electric signal will trigger little sacs that are located just below the egg membrane, cortical granules, to release their contents into the space surrounding the egg. This reaction will push the remaining sperm back. Within 48 hours, the remaining sperm will die.

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