Lipoproteins transport fats through your blood. Learn about the different classes of lipoproteins: chylomicrons, very low density lipoproteins (VLDLs), low density lipoproteins (LDLs) and high density lipoproteins (HDLs) and their jobs in this lesson.
If you had to move through water but didn’t want to get wet, what would you do? Well, one option would be to climb inside a submarine, which would keep you dry as you moved through the water. In this lesson, you are going to learn how fat molecules use this submarine-like concept to move through your blood.Fats, which we refer to as lipids when they’re inside your body, don’t like water.
If you ever poured oil into a glass of water, then you’ve seen how they just don’t like to blend. This fear of water creates a problem when fats that you eat need to get from your digestive tract to your body cells because the only available route is through your body’s waterway, known as your bloodstream.
Dietary fats get broken down in your digestive tract and are moved into the mucosal cells of the small intestine, but before they can get any farther, they must get inside water-proof vessels to prepare for transport, known as lipoproteins. So, lipoproteins are like submarines for fats because they transport lipids through the bloodstream. If you break down this term, you see that it starts with the word ‘lipo,’ which refers to lipid, and the word ‘protein.
‘Lipids don’t like water, but proteins do, so we see that lipoproteins are basically lipids, mainly in the form of cholesterol and triglycerides, on the inside surrounded by a shell of proteins. There are different types of lipoproteins, and each one carries lipids around your body in a different way. So, let’s take a look at the jobs of each of these carriers.
The broken-down dietary fats that find their way into the mucosal cells of your small intestine get reassembled into triglycerides. Triglycerides are the most common type of lipid in your body and a major source of energy, so moving them out of your digestive tract and into your body cells is an important job. This is accomplished by chylomicrons, which are a type of lipoprotein that transports lipids from the mucosal cells of the small intestine to the body cells.So, you can think of chylomicrons as the first stage of transport out of the digestive tract, and their name alludes to this fact.
The prefix ‘chylo-‘ means milky, and ‘micron’ means small, so chylomicrons are small, milky substances. When you eat a meal that is high in fat, there are so many chylomicrons at work picking up lipids that your blood appears milky.
Now, fats do not only come from your diet. Your liver can make lipids that include triglycerides and cholesterol. The transport of these lipids out of your liver falls on the shoulders of a different type of lipoprotein, called very low density lipoproteins (VLDLs).
VLDLs transport lipids from the liver to body cells, and they contain a high level of triglycerides. If you have a lot of VLDLs in your blood, then you have a lot of triglycerides in your blood, and this may increase your risk of coronary artery disease. So, you can recall this term by thinking that VLDLs are ‘very lousy and should be low.’
When the VLDL drops off its triglyceride at the body cell, the remains of the particle are either returned to the liver as a type of recycling system or transformed into denser and smaller low density lipoproteins (LDLs).
LDLs contain a higher portion of cholesterol than the other lipoproteins, so they mainly transport cholesterol from the liver to body cells.Your body uses some cholesterol in the construction of your cell membranes and certain hormones. However, too much cholesterol is not a good thing. If you have high levels of these cholesterol-carrying LDLs in your blood, it may increase your risk of heart disease. This has earned LDLs the dubious nickname ‘bad cholesterol.’ Like VLDLs, this is easy to recall if you remember that LDLs are ‘lousy and should be low.’
Now, you may have noticed that VLDLs and LDLs both carry lipids away from the liver.
You can recall this fact by remembering that LDLs ‘leave the liver.’ I point this out because there is a type of lipoprotein that returns cholesterol to the liver; they are called high density lipoproteins (HDLs).So, you can say that HDLs remove cholesterol from the body and transport it to the liver for disposal.
As you might imagine, it’s good to have high HDLs in your blood, and a high level of HDL cholesterol in your blood may lower your risk of developing heart disease. Therefore, HDLs get the nickname ‘good cholesterol.’ So, just remember that HDLs are ‘healthy and should be high.’
Let’s review. Your body uses various lipoproteins to transport lipids through the bloodstream.
Digested fats from your diet are carried by chylomicrons, which are a type of lipoprotein that transports lipids from the mucosal cells of the small intestine to body cells.Your liver can make lipids. These lipids are carried by very low density lipoproteins (VLDLs). VLDLs transport lipids from the liver to body cells, and they contain a high level of triglycerides, so you don’t want to have a lot of them in your blood.
In fact, VLDLs are ‘very lousy and should be low.’Low density lipoproteins (LDLs) contain a higher portion of cholesterol, so they mainly transport cholesterol from the liver to body cells. Too many of these may increase your risk of heart disease, so LDLs are ‘lousy and should be low’ and have the nickname ‘bad cholesterol.’High density lipoproteins (HDLs) remove cholesterol from the body and transport it to the liver for disposal.
This earns HDLs the nickname ‘good cholesterol,’ and you can remember that HDLs are ‘healthy and should be high.’
After you’ve reviewed this video lesson, you will be able to:
- Describe the structure and function of lipoproteins
- Explain what chylomicrons, VLDLs, LDLs and HDLs do in the body