What Is the Composition of Blood?

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  • 0:01 Blood
  • 0:29 Formed Elements
  • 2:20 Plasma
  • 3:58 Blood Regulation
  • 6:12 Lesson Summary
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Lesson Transcript
Adrianne Baron

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

Expert Contributor
Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

This lesson is going to cover the materials of which blood is composed. We will explore the parts that make up the solid and liquid portions of blood and discuss how these are maintained.


We all know that we have this warm fluid called blood flowing through our body. We even know that we need blood in order to stay alive. Things that you may not fully know or understand are exactly what blood is, what it is made up of, and how it is maintained. Blood is a type of tissue of our body that contains cells, chemicals, and other substances. Now on to the other two questions.

Formed Elements

About 45% of our blood is composed of what we refer to as formed elements. You likely call them blood cells. There are different types of blood cells found in our blood. Let's look at those now.

The first type of blood cells are the erythrocytes, or as they are commonly called, red blood cells or RBCs. These are the most numerous of the three types of blood cells. RBCs have the job of transporting oxygen and carbon dioxide. There are approximately 4.2 to 6.2 million RBCs per cubic mm of blood at any given point in time.

The next type of blood cell is the leukocyte, also known as white blood cells or WBCs. These are members of our body's defense team since they protect us from invading bacteria and other pathogens. There are anywhere from 5,000 to 9,000 per cubic mm of blood.

Not all leukocytes are the same. There are 5 different WBCs. The majority of our WBCs are neutrophils, making up around 65% of the WBCs. Lymphocytes make up 25% of the WBCs, and monocytes make up about 5%. Small amounts of eosinophils and basophils are also found in the blood, making up 4% and 1%, respectively.

The last of the 3 blood cell types are the thrombocytes, commonly referred to as platelets. These are also the tiniest of the blood cells. Platelets work in the body to help stop the bleeding whenever a blood vessel is damaged. We have 140,000 to 340,000 platelets per cubic mm of blood.


The other 55% of our blood is composed of plasma. Plasma is the liquid portion of blood. Since this portion is liquid, you probably have figured out that the main component in plasma is water. Water makes up about 90% of the plasma. So, what is in the other 10% of the plasma?

Well, proteins make about 8% of plasma. There are 4 different types of proteins in the plasma. The most abundant of the plasma proteins at 57% are albumins. It is responsible for helping to maintain blood volume. Globulins are another plasma protein. They make up 38% of the proteins in the plasma, and they work with the WBCs. Fibrinogen at 4% and prothrombin at 1% are the final 2 plasma proteins, and they help in the clotting process.

The smallest portion of the blood plasma is made up of an assortment of different solids. These make up the remaining 3% of the plasma. Some solids you'll find in the plasma are ions, or electrolytes, such as potassium, sodium, and calcium. Various nutrients needed by the body - like glucose, amino acids, and lipids - and waste products from metabolism - like urea, uric acid, and creatinine - are also found in the plasma. Oxygen and carbon dioxide are the blood gases which are found in the plasma as well. The last of the solids are hormones. There are a wide assortment of hormones released by various glands in the body that are transported in the plasma of the blood.

Blood Regulation

The last thing we want to understand is how the blood is maintained. With all the work our blood cells have to do, they must get replenished at some point in time. And we certainly hope the old cells are removed from the blood at some point so we don't have those building up in our blood. That is exactly what happens.

New blood cells are created through a process called hematopoiesis. This process takes place in the red bone marrow, which is found in the long bone of our bodies, such as our thigh and arm bone. This process is not happening continuously in our bodies. Instead, there is a set control mechanism in place to ensure that the proper number of RBCs are in the blood at all times.

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Additional Activities

Model of the Blood

In this lesson, students will use a variety of kitchen ingredients to create a model of human blood. Offer students a variety of ingredients for maximum creativity, such as lima beans, jelly beans, cinnamon candies, lentils, marshmallows, karo syrup, water, or oil. Students should create a model that includes plasma, red blood cells, white blood cells, and platelets in a large container, such as a beaker or clear bowl. For example, students might choose karo syrup as plasma, marshmallows as white blood cells, cinnamon candies as red blood cells, and lentils as platelets. Students should be able to explain why they chose certain materials for each part based on information in the lesson.

Student Instructions

In this activity, you'll be making a model of blood using everyday items you find in your kitchen. Your model should include plasma, red blood cells, white blood cells, and platelets and should be contained in a beaker or a large clear bowl. Some ingredients you might use are lentils, kidney beans, lima beans, candies, karo syrup, water, or oil. You should be able to justify why you chose each item to represent that part of the blood. You should keep in mind the relative amounts of each component, and make sure you stir the mixture to get an evenly distributed model. After you create your model, answer the analysis questions below.


  1. What did you choose to represent each part of the blood and why?
  2. For this experiment we used kitchen materials. What are some limitations to this model, and how would you use different supplies to create a more accurate model?

Expected Results

Students should be able to explain that plasma is a water-based liquid, which is why they chose a liquid. They should also be able to justify the relative size and shape of each of the remaining components of blood. For example, white blood cells are bigger than red blood cells or platelets. To make the model more accurate, students might choose to use clay to sculpt the specific shapes of the cells, or a mixture of liquids to create plasma.

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