What is Cholesterol? - Definition & Overview

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  • 0:00 Definition of Cholesterol
  • 1:05 Purpose of Cholesterol
  • 2:15 How We Get Cholesterol
  • 3:10 Dangers of Cholesterol
  • 4:40 Lesson Summary
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Lesson Transcript
Instructor: Adrienne Brundage
In this lesson we will discuss cholesterol and learn what it does do our bodies, both positively and negatively. Read about the sources, uses, and dangers of cholesterol, and then test your knowledge with a short quiz.

Definition of Cholesterol

It's that time of year again. You get to have your annual checkup, where the nice doctor in the white coat will listen to your heart, take your blood pressure, and look at a little vial of your blood. When those blood tests come back, he invariably has some confusing numbers he wants to talk to you about, and that means you won't be able to have steak and eggs for breakfast for a while. Your cholesterol is too high! But what, exactly, does that mean? Why do I have to watch my diet? What is the point of cholesterol, anyway? And why is it in all this delicious food? Let's find out, shall we?

Cholesterol is a waxy type of lipid, a substance that is insoluble in water, like oil or fat. Specifically, cholesterol is a type of fat that is made up of four interlocked rings of carbon called a steroid. We know steroids from watching sports, but not all steroids are responsible for building our muscles. A steroid is simply a fat with a specific chemical structure, and that chemical structure allows the fat to do its job. Cholesterol is found in every single cell of our body.

Purpose of Cholesterol

Like all fats, cholesterol has a bad reputation, but it is essential to our diets. Cholesterol acts as the precursor for other steroids in our body. When we eat cholesterol, we break it down and then use its parts to make things like testosterone and estrogen. It also acts as a precursor for vitamin D. I know what you're thinking...'Wait, don't I get vitamin D from standing out in the sun?' Yep, you do, but your body can't make vitamin D out of thin air. It uses sunlight to start a cascade of chemical reactions that break down cholesterol and use the parts to make the vitamin. Without cholesterol, you could stand out in the sun all day and still not make enough vitamin D for your body.

Cholesterol is also an important component of our cell membranes. It makes sure our cellular membranes work the way they should. It acts like a patch, keeping very tiny molecules from going in and out of our cells when they're not supposed to. Cholesterol also keeps the cell membrane nice and flexible, which allows our cells to do what they need to do. Without cholesterol, our cell membranes would be too stiff to form tissues like skin and muscle and would be leaking molecules like mad. That would be a very bad way to start the day!

How We Get Cholesterol

So where does cholesterol come from? Well, cholesterol is so important that we both make it and eat it. Every cell in our body can make its own cholesterol to some extent, but our livers are responsible for producing cholesterol in the largest amount. A portion of our daily cholesterol is produced in liver cells, and our intestines, reproductive organs, and adrenal glands help out by producing a little bit themselves. This homemade cholesterol is then sent to whatever cell in the body needs cholesterol at that moment.

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