Blood

What is blood?

Blood is an essential fluid, constantly flowing and keeping your body working. It carries oxygen and nutrients to your body’s tissues. And it removes waste your body doesn’t need. It has four parts:

• Plasma is the liquid part of blood that carries blood cells throughout your body.
• Red blood cells carry oxygen to your body’s cells.
• White blood cells fight infections.
• Platelets form blood clots to help stop the bleeding if you’re injured.

These basic parts are the same no matter your blood type. The most common blood types are A, B, AB and O.

What does blood do?

Blood performs many vital functions. You need blood because it:

• Carries oxygen and nutrients to your body’s cells and tissues.
• Carries waste products away from your cells and tissues.
• Protects your body from infections.
• Makes clots that can stop the bleeding after an injury.
• Regulates your body temperature and blood pressure.

Where is blood located?

Blood flows throughout your circulatory system. Your heart pumps blood to blood vessels that move blood throughout your body:

• Arteries carry oxygen-rich blood from your heart to your body’s tissues.
• Veins carry oxygen-poor blood from your body’s tissues back to your heart.
• Capillaries carry blood between your arteries and veins.

Where is blood made?

Blood gets its start in your bone marrow (the spongy tissue inside bones). Bone marrow contains stem cells. Stem cells are the earliest form of your body’s blood cells. Blood cells mature from stem cells in your bone marrow. Once they’re fully developed, they enter your blood vessels as whole blood.

What is blood made of?

Blood is mostly fluid. But it also contains cells and proteins that make it (literally) thicker than water. The average adult male has about 5 liters (10.5 pints) of blood. Females have about 4 liters (8.5 pints). Blood makes up about 8% of your body weight:

• Plasma makes up about 55% of your blood.
• Red blood cells make up about 44% of your blood.
• White blood cells and platelets make up about 1% of your blood.

Plasma

Plasma is a yellowish fluid that’s more than 90% water. Its main job is to transport. It carries blood cells and essential proteins and salts throughout your body. It also carries waste products from your cells to your kidneys and liver to remove the waste. It maintains your body temperature and keeps blood cells moving through your body.

Red blood cells

Red blood cells (erythrocytes) get their color from the protein hemoglobin. Hemoglobin helps red blood cells deliver the oxygen other cells need to make energy. Your red blood cells also carry waste (carbon dioxide) to your lungs for you to breathe out. They live about 120 days before your body makes new cells to replace them.

White blood cells

White blood cells (leukocytes) are part of your immune system. When germs or cancer cells launch attacks, your white blood cells find and destroy them. You have five types. Each has a unique task and timeline. More than half of your white blood cells are neutrophils, the most common type.

Platelets

Platelets (thrombocytes) are plate-shaped cell fragments. They’re first on the scene any time your blood vessels are damaged and bleeding. Platelets seal damaged blood vessels by forming clots. That way, blood stays in and germs stay out. Platelets have a lifespan of about a week.

What color is blood?

Your blood — like your red blood cells — is red. It’s bright red when it’s leaving your heart and filled with oxygen. It’s more of a dull brick red when it’s running low on oxygen and making the return trip back to your heart for more.

What common conditions and disorders affect blood?

Both cancer and noncancerous disorders can impact how your blood works.

Blood cancer

Blood cancer starts when there’s a change (mutation) in the genes that tell your body how to make blood cells. The mutation causes your body to make abnormal blood cells that multiply fast. Blood cancers include:

• Leukemia
• Lymphoma
• Myeloma

Blood disorders

Blood disorders are noncancerous conditions where blood cells can’t do their jobs correctly. They range from harmless conditions to potentially life-threatening ones. They include:

• Anemias: Anemia is the most common blood disorder. It happens when you don’t have enough healthy red blood cells. There are many types, but the most common is iron-deficiency anemia.
• Blood clotting disorders: A blood clotting disorder affects your platelets or your clotting factors. Clotting factors are proteins in your blood that help your platelets manage bleeding.
• Bleeding disorders: These conditions happen when your blood doesn’t clot normally. This causes you to bleed more than usual. Hemophilia is a well-known example.

Signs and symptoms your blood isn’t working right

Blood tests alert healthcare providers to conditions impacting your blood. Blood test results let your provider know if you have high or low blood cell counts or abnormal blood cells. This information helps providers diagnose countless conditions.

The most common symptoms of problems with your blood include:

• Fatigue and weakness (a sign of anemia)
• Getting sick frequently or easily (a sign of low white blood cells)
• Bruising or bleeding easily (a sign of low platelets)

An enlarged spleen is another common sign of blood problems. This is because your spleen filters your blood. Conditions affecting your blood cells can cause it to swell.