What Is the Composition of Blood?

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
Instructor: Adrianne Baron

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

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.

Blood

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.

Plasma

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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