Overview

Blood is mostly fluid but contains cells and proteins. Blood has four parts: Red
blood cells (bottom right), white blood cells, platelets (middle right) and plasma (top
right).

What is blood?

Blood is an essential life force, constantly flowing and keeping your body working. Blood
is mostly fluid but contains cells and proteins that literally make it thicker than water.

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Blood has four parts: Red blood cells, white blood cells, platelets and plasma. Each part
has specific and important tasks, from carrying oxygen to carrying out waste products.

Your blood also acts like a kind of health barometer. Unusual blood test results may be
the first sign of changes that could point to serious illness. This article focuses on how
blood works and conditions that affect blood health.

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Function
What does blood do?

Blood flowing through your blood vessels is responsible for many things:

 It carries oxygen and nutrients throughout your body.

 It forms blood clots to manage bleeding.

 It protects your body from infections.

 It carries waste products.

 It regulates your body temperature.

Blood has four parts. Red blood cells and plasma make up most of your blood. White
blood cells and platelets, sometimes referred to as the buffy coat, account for less than
1% of your blood.

Red blood cells

Red blood cells (erythrocytes) account for 45% of your blood. They carry oxygen
throughout your body. They also help to clear waste from your body. These cells:

 Get their distinctive color from the protein hemoglobin. Hemoglobin helps the red
blood cells deliver the oxygen other cells need to produce energy.

 Can squeeze through the tiniest sections of your circulatory system. (Your
circulatory system includes the network of capillaries, veins and arteries that
blood moves through on its journey throughout your body).

 Have a short life span. Red blood cells live for about 120 days before they’re
replaced with new cells.

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White blood cells

Your white blood cells (leukocytes) account for less than 1% of your blood and are part
of your immune system. When invaders such as viruses or cancerous cells launch
attacks, your white blood cells move quickly to find and destroy them. White blood cells
can move from capillaries into your tissues. There are five types of white blood cells:

 Neutrophils kill bacteria and fungi and remove foreign debris.

 Lymphocytes consist of T-cells, natural killer cells and B-cells that protect
against viral infections and produce antibodies that help you fight infection.

 Basophils react to allergens.

 Eosinophils find and destroy parasites and cancerous cells and assist basophils
with your allergic response.

 Monocytes find and destroy viruses, bacteria, fungi and protozoa. They also
remove damaged cells.
Platelets

Your platelets (thrombocytes) are first on the scene any time your blood vessels are
damaged and bleeding. Platelets manage bleeding by forming blood clots that seal
damaged blood vessels so you don’t lose large amounts of blood. Platelets:

 Account for less than 1% of your blood. There are tens of thousands of platelets
in a single drop of your blood.

 Get their name from how they work in your blood. Platelets are the lightest part of
your blood. They form in the shape of plates, flattening themselves against blood
vessel walls as plasma and blood cells flow by.

 Have a coat of sticky proteins that act like Velcro®, helping platelets cling to
broken blood vessels.

Plasma

Your blood cells and platelets float in your plasma. Plasma is a yellowish fluid that
accounts for 55% of your blood. Plasma is your blood’s utility player, covering many
bases as it works to keep your body functioning. Some tasks plasma does include:

 Helping to clot blood and defend against invaders.

 Delivering hormones, nutrients and proteins to parts of your body and helping to
exchange oxygen and carbon dioxide.

 Removing waste from cells and transporting it to your liver, lungs and kidneys for
excretion.

 Maintaining your blood pressure and circulation.

 Regulating body temperature by absorbing and releasing heat.

What are blood types?

There are four blood types. The types are different depending on whether blood
contains certain antigens. Antigens are substances that make your immune system
react.
Anatomy
Where is blood located?

Blood flows throughout your body. It gets its start in your bone marrow, which contains
stem cells. Stem cells create trillions of cells, including blood cells. Blood cells develop
and mature in your bone marrow before they enter your blood vessels. Blood represents
about 8% of your body weight.

Conditions and Disorders

Blood cancer, blood disorders and a common cardiovascular disease affect blood.
Blood cancers affect how your body produces blood cells. Blood disorders keep your
blood from doing its job. Atherosclerosis is a cardiovascular disease that affects blood
flow. In general, blood cancer and blood disorders have more overall impact on blood
health than atherosclerosis.

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Blood cancers

Blood cancer happens when something disrupts how your body makes blood cells. If
you have blood cancer, abnormal blood cells overwhelm normal blood cells. There are
three blood cancer types:

 Leukemia, the most common blood cancer.

 Lymphoma, which is cancer of your lymphatic system. Your bone marrow, which
produces blood cells, is part of your lymphatic system.

 Myeloma, which starts in your bone marrow and affects your plasma cells.

Blood disorders

Blood disorders are noncancerous conditions that keep parts of your blood from doing
their jobs. Blood disorders include anemias, blood clotting disorders and bleeding
disorders.

Some blood disorders may not cause symptoms or require treatment. Others are
chronic (lifelong) illnesses that require treatment but typically won’t affect how long you’ll
live. There are also blood disorders that are serious illnesses and can be life-
threatening.
Healthcare providers treat blood disorders by managing symptoms and treating any
underlying conditions.

Anemias

Anemia is the most common type of noncancerous blood disorder. It happens when you
don’t have enough healthy red blood cells. Sometimes people inherit anemia, but they
may also acquire or develop it. There are many types of anemia. Some common
anemias include:

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 Iron deficiency anemia.

 Pernicious anemia.

 Sickle cell anemia.

Blood clotting disorders

A blood clotting disorder affects your platelets or your clotting factors (coagulation
factors). Clotting factors are proteins in your blood that help your platelets manage
bleeding. You may develop a blood clotting disorder (acquired blood clotting disorder) or
inherit a genetic mutation that causes abnormal blood clotting.

Prothrombin gene mutation and Factor V Leiden syndrome are examples of inherited
blood clotting disorders. Antiphospholipid syndrome (APS) and disseminated
intravascular coagulation (DIC) are examples of acquired blood clotting disorders.

Bleeding disorders

Bleeding disorders happen when your blood doesn’t clot normally, causing you to bleed
more than usual. Von Willebrand disease is the most common bleeding disorder in the
U.S. Hemophilia, a rare inherited condition, is another example of a bleeding disorder.

A note from Cleveland Clinic

Your blood is a precious resource, constantly taking care of your body so it works as
well as it should. Your blood carries oxygen to your cells so they can create energy. It
helps your immune system defend your body against intruders. Blood also manages
how much you bleed when you’re injured. While you can take care of your blood, you
may not be able to avoid diseases that affect it. Fortunately, healthcare providers can
treat most serious blood conditions, including blood cancers and blood disorders.

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