What are the Components of Blood and Their Functions?

Most people understand the basics of blood and what it does to our bodies. Unfortunately, the basics aren’t always enough to know how blood works, and the functions it carries out. It’s easy to describe it as a red fluid that circulates throughout our bodies. And, we all know we need it to survive. But, what are the components of blood and their functions?

To better understand the functions of blood and how they work, it’s important to know about everything that blood does within the body. This is never more critical than when you get a blood test to detect health issues.

There are so many different functions of blood before even breaking down the components. In this article, we’ll talk about those functions, and how blood works within our bodies. We will also cover the four major components that make up your blood, and what they do.

This specialized fluid is designed to supply our bodies with the nutrients they need, so it’s important to know as much about blood as possible. If you plan on training to become a phlebotomist, having a deep knowledge of blood’s components is essential. If not, it still can be helpful to know how these components function, and what they do for you on a daily basis.

What is Blood?

Blood makes up between 7% to 8% of the body weight of a human. That equals up to six quarts of blood in an adult. The most significant function of blood, as most people know, is to carry oxygen and nutrients throughout the body. Simply put, without blood circulating through our system, we would die instantly.

Aside from these major functions, however, blood carries out so much more. Some of the biggest functions of blood include:

  • Removing waste products from the body, like carbon dioxide
  • Transporting hormones
  • Regulating acidity levels (pH)
  • Regulating body temperature
  • Hydraulic functions

What are the different Components of Blood?If you’re cold in the winter, it’s your blood that is protecting your internal organs and keeping them warm. If you’re exercising, blood flows to the surface of the skin and allows for heat loss. If you have a cut on your hand, blood protects it from infection. There are so many examples of how blood helps us to perform the most basic functions.

Blood is considered to be a specialized tissue. Within it, there are over 4,000 different components. However, four main components carry out many of its basic functions. Everyone produces these components in the same way, and they carry out the same functions for each person.

What are the Main Components of Blood?

The main four components of blood are:

  • Red blood cells
  • White blood cells
  • Plasma
  • Platelets

Each of these components carries out a specific function within the blood. They’re all necessary for the body to perform normally. Let’s break down the components a bit more to learn about what they are, and what they do.

Red Blood Cells

Red blood cells are also known as erythrocytes. They are relatively large cells and account for 40% to 50% of your blood’s total volume. If you were to look at red blood cells underneath a microscope, they would appear as flat, disk-shaped cells.

Red blood cells are mostly made up of hemoglobin. In fact, hemoglobin makes up about 95% of a red blood cell. It is an iron-rich protein that takes oxygen from the lungs and transports it throughout the body. Red blood cells also carry carbon dioxide away from the cells and help to get rid of waste.

These cells die regularly. Most red blood cells don’t last longer than about four months. During that time they are degraded. However, the body is continually producing new ones.

how long do red blood cells live?

People who deal with anemia typically have fewer red blood cells in their body. Because of this, they may often feel fatigued. This is due to a shortage of oxygen being evenly circulated throughout the body. Our bodies need enough red blood cells to function correctly, have energy, and get rid of waste. As you might suspect, red blood cells are also what gives our blood its red color.

White Blood Cells

White blood cells, commonly known as leukocytes, are the cells that help our immune system. Strangely enough, they only make up about 1% of the blood volume in an average, healthy person. That 1% is usually enough to keep us strong and healthy.

However, leukocytes like this are not just limited to blood. They are found elsewhere in the body and can help to prevent infections of many kinds. That means these cells can make movements from the bloodstream to areas of the body that need it most. They may be small, but they spring into action to protect the body very quickly.

White blood cells work by clinging to foreign proteins in the body like bacteria and fungi. It doesn’t take long for the cells to surround the infected area, and attempt to heal it. They even help to fight against things like cancer cells and other infectious diseases. They can also get rid of any foreign matter in the body, and old blood cells. It’s easy to think of white blood cells as ‘housekeepers’ of the body.

Unlike red blood cells, white cells only live an average of 18 to 36 hours. While there are plenty of different subtypes, and some can live nearly a year, most die relatively quickly. Without some white blood cells in our bodies, sickness and infection would overtake us almost immediately.

Low White Blood Cell Count

It can be caused by a variety of different things, including:

  • Diminished bone marrow function
  • Cancer
  • Autoimmune diseases
  • Certain medications

It’s rare to discover that you have a low white blood cell count simply by chance. It requires testing. These tests are usually performed if you already have an existing condition. If it is found that you do have a low white blood cell count, it’s important to take precautionary measures in everything you do. You’ll be far more prone to sickness and infection. Talk to your doctor about the steps you can take to protect yourself.


Plasma is a clear/yellow-tinted watery substance that makes up about 55% of our blood’s volume. It contains the other components of blood, and many other substances to make up that amount of volume. Some of the other substances include things like protein, albumin, globulin (globular proteins), and sugar.

What's the main function of white blood cells?

It’s a fair assessment to think of plasma as a sort of watchman for blood itself. While it contains mostly water, it also contains:

  • Blood cells
  • Glucose
  • Carbon dioxide
  • Hormones
  • Protein

Plasma provides nourishment to our blood cells and also helps to remove waste products. Research has shown that over 500 different types of protein have been found in plasma to this day. It is believed that plasma holds some of every type of protein the human body can produce.

One of these proteins is albumin, created by the liver. Albumin helps to keep plasma contained inside our blood vessels. If plasma can leak out, when albumin levels are low, it can get into the tissue causing problems like edema.

People often donate plasma similarly to how blood itself is donated. Plasma that is donated is separated from the other components of blood. It is just as important to donate plasma as it is to donate blood. As you can see, it provides so much of what our bodies need to function correctly.


Platelets help to clot blood properly. They are also called thrombocytes. They don’t have nuclei and work with chemicals to help blood clot when you have an injury. This is because they don’t have enough clotting power on their own. They help the blood to clot by sticking to the blood vessel walls.

For proper clotting of the blood to occur, platelets need to work with twelve other clotting chemicals. If they don’t all work together, blood won’t clot properly, which could lead to minor injuries becoming far more serious. This can also occur if you have a low platelet count. Some symptoms of a low platelet count include:

  • Frequent nosebleeds
  • Bleeding gums
  • Dark bruises
  • Blood in urine/stools

In mild cases of low platelet counts, your doctor may simply choose to monitor you, and suggest a few lifestyle changes. In more severe cases, you may need a blood transfusion or steroids to help.

Platelets also help to fight infection. They can release certain proteins that target and kill different types of bacteria and microorganisms.

Compared to other blood cells, platelets also have a relatively short lifespan, usually just living for about ten days. However, they are produced in a similar fashion as red and white blood cells.

What is Blood?

Where Are Blood Cells Produced?

Red and white blood cells, as well as platelets, are all produced in inside bone marrow. Bone marrow is a gel-type substance that fills the inside of our bones. The components of bone marrow, including various types of cells and fats, produce blood cells regularly.

Specific areas of bone marrow are more influential in producing blood cells than other, depending on the area of the body. The areas most responsible for creating blood cells are vertebrae, sternum, ribs, skull, and hips.

Why Do People have Different Blood Types?

So, if everyone has the same major components that make up your blood, why are there different blood types? There are four main blood types: Type A, type B, type O, and type AB.

Type A blood has likely been around the longest, and type B is thought to have originated about 3.5 million years ago, as a result of sugar modification on top of red blood cells. The different types of blood each person has is just that; modifications of the antigens on top of red blood cells.

Antigens are small markers that communicate with your immune system. Over time, evolution and different mutations have changed the sugars and genes that determine which antigens are on our red blood cells. These mutations have made certain blood types incompatible with each other.

If you’re unsure about your own blood type, a great way to learn is to donate. People with type O blood are considered to be universal donors since their blood can work with any other type. However, if you have A or B, your blood will only be able to combine with those specific types. Blood banks across the country are always looking for donors with every blood type. Just one pint of donated blood can save up to three lives.

Breaking Down the Parts of Blood

Though there are thousands of components and functions of blood, the main four work together to make everything run efficiently and smoothly within our bodies. Without just one of these four main functions, we would be open to diseases, infections, and so much more.

If you’re performing a blood draw, knowing these components of blood can make your job much easier. Not only are you able to explain to patients what type of testing is being done, but you will understand the results when they are provided by lab testing. Taking someone’s blood and being able to let them know if something is abnormal can be the first step in treating a disease.

Even if you aren’t interested in phlebotomy, you should be aware of these components and what they do. Know the symptoms of any abnormalities that may be occurring with the components so that you can talk to your doctor as soon as possible. It’s also important to be knowledgeable of your blood type, should you ever need it yourself.