Lesson Video: Components of the Blood Biology

Video Transcript

In this video, we will learn to describe the structure and function of the major components of the blood, those components being red blood cells, white blood cells, platelets, and plasma. Then we’ll try some practice questions and at the end we’ll summarize what we’ve learned.

We tend to simply think of blood as a red liquid that oozes from our body when we accidentally cut a finger or scrape a knee. But your blood is actually a type of connective tissue, which means that it is composed of many cells suspended in a nonliving matrix or a substance. The two main types of cells in your blood are red blood cells, commonly shortened to RBCs, and white blood cells, commonly shortened to WBCs. Also found in your blood are small cell fragments called platelets. And all three of these components are suspended in an amber-colored liquid called plasma. And this heterogeneous mixture is what we refer to as blood.

All of the blood in your body is contained within your circulatory system, which consists of your heart, which pumps the blood, and the complex closed network of blood vessels that carry the blood from place to place. Blood has several important functions. Its primary function is transport. Blood transports gases like oxygen and carbon dioxide. It transports nutrients like glucose. It also transports waste products and hormones. Blood also helps to prevent infection. It helps your body to maintain a uniform and appropriate temperature. Your blood also helps to maintain fluid and chemical balance within the body. The red blood cells, white blood cells, platelets, and plasma are all adapted to allow the blood to carry out these essential functions.

Next, let’s take a closer look at each of these four components. First, we have red blood cells, also called erythrocytes. Erythro- is a prefix that means red, and -cyte is a word part that means cell. The primary function of erythrocytes is to carry oxygen from the lungs to the rest of the tissues of the body. These cells are the most numerous in your blood, and they have several adaptations that allow them to carry out their essential function.

Most notably, they have a distinct red color. This color comes from a molecule called hemoglobin, which is rich in iron. Hemoglobin is a molecule that helps the red blood cells to carry oxygen. Another important feature of mature red blood cells is that they do not possess a nucleus. They also don’t have mitochondria or many other organelles. They’re basically just sacs filled with cytoplasm that’s rich in hemoglobin.

This lack of a nucleus gives red blood cells their distinct shape. They’re shaped like a disk with indents on each side. This shape is called biconcave. Bi- is a prefix that means two, and concave is what we call an indented shape. I like to remember this because caves are like indents in rocks. This shape increases the surface area of the cell in relation to the cytoplasm inside, which allows more oxygen to diffuse into the cell more quickly. These special features in the structure of the red blood cell directly support their function of carrying oxygen throughout the body.

Next, let’s look at some of the special features of platelets. Platelets are also scientifically known as thrombocytes. Thrombo- is a word part that means clot, and platelets serve the purpose of causing blood clotting. And -cyte does mean cell, but platelets are technically small fragments of much larger cells. If you were to injure yourself and tear a blood vessel, causing bleeding, the damaged epithelial cells would release chemical signals, which activate the platelets in your bloodstream, causing them to stick together and form a plug over the wound.

This plug serves two purposes. First, it prevents you from bleeding indefinitely and losing too much of your blood too quickly. Secondly, it prevents pathogens from entering the bloodstream, where they could cause a serious infection. Blood clotting is an important adaptation that helps to protect our bodies. But sometimes blood clots can be dangerous. Sometimes blood vessels become damaged because of disease. If a blood clot occurs in the blood vessels that carry oxygenated blood to the heart or to the brain, it can cause a heart attack or a stroke, which is one of the reasons why it’s so important to keep your circulatory system healthy.

Next, let’s take a closer look at white blood cells. White blood cells are also called leukocytes. Leuko- is a word part that means white, and I’m sure you know by now that -cyte means cell. White blood cells, unlike platelets and red blood cells, actually possess a nucleus. White blood cells are responsible for protecting our bodies from infection by identifying and destroying antigens. They’re an important part of our immune system.

There are many different types of white blood cells, which each play a specific role in our immune response. One of these types is called a lymphocyte. These cells are more common in our lymphatic system than in our blood. And they play a wide range of roles when it comes to fighting infection. Another important type of white blood cell is called phagocytes. And these cells are able to surround and engulf foreign particles that are found in the blood.

Now that we’ve investigated red blood cells, which carry oxygen, platelets, which are responsible for blood clotting, and white blood cells that fight infection, let’s take a look at the material that holds it all together, blood plasma. Our blood plasma is an amber-colored liquid that’s mostly water. And it serves the purpose of carrying the red blood cells, white blood cells, and platelets throughout the blood vessels.

Besides water, plasma contains and transports many materials our body relies on to function properly. These include electrolytes, proteins, hormones, nutrients, and waste products on their way to be removed from the body. The average human adult has about one and a half gallons, or around five liters, of blood circulating throughout their body. If we were to separate blood into its components, about 45 percent of the blood would consist of red blood cells, about one percent would be platelets and white blood cells, and about 55 percent of your blood would be plasma.

Now that we’ve learned about the components of our blood and the adaptations that allow them to carry out their function, let’s try a practice question.

Which of the following is not a major component of blood in humans? (A) Epithelial cells, (B) red blood cells, (C) white blood cells, (D) plasma, or (E) platelets.

This question is asking us to recall the major components of blood and then choose the response that is not one of those components. So first, let’s recall that there are four major components to human blood. We’ll briefly review them before we select our answer.

Here we have a diagram of a blood vessel. And we’ve exposed a view of the lumen so that we can see the blood flowing through it. The blood vessel has an inner lining composed of a layer of epithelial cells. The main component of our blood is plasma, an amber-colored liquid.

Plasma transports electrolytes, proteins, hormones, nutrients, and waste from place to place in the body. It also carries the different types of blood cells. Red blood cells are cells that are specifically adapted to transport oxygen. White blood cells are immune cells that help our bodies to identify and fight off pathogens. And platelets are small cell fragments that form blood clots in order to prevent bleeding and infection. Red blood cells, white blood cells, platelets, and plasma are the four components that make up human blood. Epithelial cells are lining cells and not a part of the blood itself.

Returning to our answer choices, which of the following is not a major component of blood in humans? Well, epithelial cells are not a component of our blood.

Let’s try one more practice question.

What is the scientific name given to red blood cells in humans? (A) Phagocytes, (B) hemocytes, (C) lymphocytes, (D) erythrocytes, or (E) oocytes.

This question is asking us to select the option that’s telling us the scientific name that we use for red blood cells. This is where being familiar with the different parts that make up scientific words really comes in handy. We can break the words in our answer choices down into five different prefixes and just one suffix. The word part -cyte means cell, which tells us that all of our choices actually name different types of cells.

Phago- is a word part that means eating. And phagocytes are cells that are able to surround and engulf particles or other cells. Hemo- is a word that means pertaining to the blood. And hemocyte is a general term for blood cells. It applies to more than one type of cell in more than one type of organism. Lympho- is a word that means pertaining to the lymphatic system. Lymphocytes are a type of immune cell. Erythro- is a word part that means red. So an erythrocyte would be a red cell. That sounds right, but let’s keep going. Oo- is a word part that means egg. So oocytes are egg cells.

Let’s return to our answer choices. Some of these are obviously incorrect. And on first glance, you might be tempted to choose hemocytes, especially if you remember that red blood cells contain hemoglobin. But hemocyte is a general term for all blood cells and actually usually refers to the blood of invertebrates, not humans. Erythro- is a word part that means red. So the correct scientific name given to red blood cells is erythrocytes.

Let’s go ahead and wrap up our lesson by reviewing what it is we’ve learned. In this lesson, we learned about the function of blood. We learned about the four components of blood: red blood cells, white blood cells, platelets, and plasma. And we learned about the scientific names, adaptations, and different functions of each of these components.