Overview of Human Reproduction

Instructor: Adrianne Baron

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

This lesson will provide a general overview of the process of human reproduction. We will cover the basics starting from the point of fertilization through the point of birth.

Human Reproduction

Carl and Ashley have made the decision to start their family. They are learning everything they can about the process of human reproduction, or the production of human offspring, so that they know what to expect from conception to when their bundle of joy arrives. Ashley decides to talk to the nurse at her doctor's office to get more information.


Aly, Ashley's nurse, begins by explaining that reproduction is accomplished using Ashley's ova, or eggs, and Carl's sperm. During intercourse, the sperm and ova will fuse together. This process is known as fertilization.

Fertilization takes place in the fallopian tubes
Diagram showing fertilization

Fertilization will take place in one of Ashley's fallopian tubes. Their fertilized egg is now considered to be a zygote. The zygote will divide continuously, doubling the number of cells in the zygote with each division. As it is doing this, the zygote will move toward Ashley's uterus.

Their zygote will implant itself into the inner lining of Ashley's uterus known as the endometrium. The attachment, called the placenta, serves as a source of nourishment and way to remove waste. The nutrients and waste will pass through the umbilical cord which connects the zygote to the placenta. The zygote is beginning to develop into a human offspring, but is still at the point where it does not look like a human yet. The baby from about 2 to 8 weeks of development is called an embryo.


Aly says that Ashley will likely be able to tell that she is pregnant around week 9 which is the point when the developing baby is now called a fetus. Their fetus has now developed human structures and looks like a human about an inch long. Aly tells her that by the end of her first trimester, which is week 13, the fetus will be able to open its hands and use its kidneys. During this time the brain will be growing at a very fast rate.

Fetus at about 5 to 6 months
Diagram showing a fetus and placenta

Carl and Ashley's fetus will continue to grow larger during the second trimester, or weeks 14 through 27. Aly says that this is the trimester when the bones of the fetus will become harder and the fetus practices breathing by sucking amniotic fluid in and out of the nose and mouth. During this trimester, their developing baby will also begin to develop his or her senses such as taste, hearing, and changes in light. Aly informs Ashley that this is usually an exciting time during her pregnancy. Ashley will be able to feel her fetus move, and the genitals will have developed enough that they can find out the sex of the baby.

Aly explains that the last trimester runs from week 28 through birth. Carl and Ashley's fetus will continue getting bigger and will start to fill out some by developing fat. This is a critical time during development since many nerve cells are produced. The lungs, brain, and liver are all continuing to mature to the point that they can support the baby after birth. Aly tells Ashley that somewhere around week 36 or so, the fetus will begin to move lower in her body towards her pelvis in order to prepare for birth. The fetus will also get into a head down position to ensure the head comes out first.

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