Functions of Red Blood Cells, White Blood Cells & Platelets

Functions of Red Blood Cells, White Blood Cells & Platelets
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  • 0:06 Blood Connective Tissue
  • 0:38 Red Blood Cells
  • 1:48 White Blood Cells
  • 3:58 Remembering White Blood Cells
  • 4:10 Platelets
  • 4:28 Lesson Summary
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Lesson Transcript
Instructor: Laura Enzor

Laura has a Master's degree in Biology and is working on her PhD in Biology. She specializes in teaching Human Physiology at USC.

Blood is a connective tissue vital to our body's survival. In this lesson, we will explore the three functions of blood by delving into red blood cells, white blood cells and platelets - the three individual components that make up blood as a whole.

Blood, A Connective Tissue

Types of living cells in the blood
Blood Cell Types

In the human body, one of the most important connective tissues is blood. Blood is considered a connective tissue because it consists of a non-living fluid in which living cells are suspended. The blood matrix surrounding the cells is known as plasma, which accounts for about 55% of our blood volume. There are three types of living cells in blood: red blood cells (or erythrocytes), white blood cells (or leukocytes) and platelets (or thrombocytes). These make up the remaining 45% of our blood volume.

Red Blood Cells

Blood has three main functions: transportation, regulation and protection.

Our erythrocytes, or red blood cells, are the most abundant cell type in the human body. Additionally, erythrocytes are anucleated, which means they don't have a nucleus. This extra room allows for more hemoglobin to be stored in our red blood cells. Hemoglobin is a respiratory pigment, which binds to either oxygen or carbon dioxide. This allows oxygen to be transported around our body to our tissues and organs (and carbon dioxide to be taken away). Hemoglobin is largely comprised of iron, which when combined with oxygen, gives blood its red color. Additionally, blood helps cycle nutrients and hormones throughout our bodies.

Process of transporting oxygen throughout the body
Oxygen Transportation

Blood also helps us maintain homeostasis by regulating our internal body pH and temperature as well as how much water is in our bodies at a given time. Plasma, our connective tissue matrix, is about 90% water. Blood is also vital in protecting our bodies. Blood loss is controlled with clotting mechanisms, and white blood cells provide immune response. Let's examine this function in more detail.

White Blood Cells

The types of leukocytes in the blood
White Blood Cell Types

There are five different types of white blood cells, or leukocytes, in our bodies, and we can break them up into two main categories. These are granulocytes and agranulocytes. These terms simply refer to how these cells look when stained. Granulocytes have visible granules in their cell bodies, and agranulocytes do not. There are three types of granulocytes. They are neutrophils, eosinophils and basophils.



Neutrophils are the most abundant type of white blood cell in our body. These are primarily responsible for killing off foreign bacteria. Neutrophils are the first responders when we are injured or sick, and they help keep us healthy by phagocytizing (or consuming) bacteria in our bodies.


Eosinophils are responsible for fighting infections of parasitic worms. These cells release toxins that kill the worms and are also involved in the inflammatory response when we have an allergic reaction.


Basophils release two chemicals, histamine and heparin. Histamine is also involved in allergic reactions, and heparin is an anticoagulant. Anticoagulants keep blood from clotting, which helps bring more blood to a damaged area in our body, which, in turn, helps promote healing.


The two remaining types of leukocytes are agranulocytes. These are monocytes and lymphocytes.

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