Blood: Components, Functions

Blood: Components, Functions


This lesson will identify the functions of the three components that make up blood as well as identify the 4 blood types.

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Blood Components, Functions

Source: Video and Images Created by Amanda Soderlind

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Welcome to this lesson today on blood. Today we are going to be discussing the components and the function of blood within the body. So blood is a very important part of our body. It's important because it helps to transport oxygen and other important ions and nutrients to our tissues and to our cells. And it also helps to get rid of carbon dioxide.

And so in the human body, we have around five liters of blood that are pumping around your entire circulatory system. So we're going to be talking about the different components of blood today. So blood is made up of three main components, plasma, blood cells, and platelets.

So plasma makes up around 55% of your total blood. And plasma is mostly water. And what it does is that it transports blood cells, proteins, iron, glucose, gases, other important nutrients and ions throughout your blood.

So the proteins that it helps to transport have different functions. So different types of proteins that are transferred by plasma have functions such as they are part of hormones or they play a role in the immune system or they play a role in clotting. So these different things that plasma is transporting play large roles throughout your body.

And then another component of blood is blood cells. And so we actually have two different types of blood cells, erythrocytes and leukocytes. And we're going to come back to these in just a moment here.

And then platelets are the third component of blood. And platelets, basically their role is in clotting blood. They help to clot blood.

So let's go back and talk a little bit more in depth about erythrocytes and leukocytes. Erythrocytes are another word for red blood cells. And erythrocytes make up around 45% of your blood. So between plasma and red blood cells, you can see that's making up the vast majority of your blood.

Erythrocytes sites carry oxygen, so their main function is to carry oxygen. So they're a very important component of blood, because they have that ability to carry oxygen. And the reason that they have this ability to carry oxygen is because they contain a protein called hemoglobin. And hemoglobin is a protein found in red blood cells which binds to oxygen. So red blood cells carry oxygen. And they also help to get rid of excess carbon dioxide that's built up in the cells and tissues as well.

So erythrocytes, or red blood cells, also help determine our blood type. So our blood type is determined by antigens on these red blood cells. So we can have blood types such as A, B, AB, or O. So these blood types, as I mentioned, are determined by antigens that are present on our erythrocytes, or our red blood cells. So those are the components of red blood cells.

Leukocytes are white blood cells. And there are actually a total of five different types of white blood cells. And these five different types of white blood cells all play a role in our body's defense system. So they play a role in our body's defense system and help us fight off different pathogens that might enter our body. So they're actually a really small fraction of our blood.

So if we take a look at these pictures down here, we're going to take a look at this one first just so you can kind of have a visual of what these different components of blood look like. So we have our red blood cells right here. And our red blood cells, you can kind of guess by the name, they are red in color.

And basically, they're kind of shaped like a thin disk with a dimple in the middle. So their shape is important in their functioning. So sickle cell anemia is a type of disease where these red blood cells become misshapen.

And then we also have our white blood cells. And this is just kind of a very general picture. Remember I had mentioned that there are five different types of white blood cells that all look a little bit different and play different roles in our body's defense system. And then we also have platelets. And remember, platelets play a role in our blood's clotting.

And then if we take a look over here, we can see these three different components of blood that I've talked about. If you were to centrifuge blood-- which basically means it gets put into a machine and it gets spun really, really, really fast, and this separates the different components of blood-- so plasma then would settle out on the top. And then on the bottom, you would have the heavier components of blood, which would be the blood cells and the platelets.

So if you've ever known somebody before who's donated plasma, generally what happens is the blood is taken out of them, centrifuged so that the plasma is separated out, and then the red blood cells and platelets are then put back into them. So plasma is again that component of blood that's mostly water. And it transports a lot of different materials throughout the blood.

So this lesson has been an overview on blood, its components, and their functions.

Terms to Know
Blood Cells

A component of blood that includes both red and white blood cells each of which play a different role in the body.


Erythrocytes are red blood cells whose main role is to transport oxygen and carbon dioxide to and from body tissues.


Leukocytes are white blood cells that participate in the body’s defense system.


A component of blood that helps to transport various substances such as blood cells, platelets, iron and proteins.


A component of blood that assists in clotting.