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Overview of Blood

By

The Manual's Editorial Staff

Last full review/revision Apr 2020| Content last modified Apr 2020
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Blood is the red fluid in your arteries and veins. It provides the oxygen, water, and nutrients that your tissues and organs need to survive. You have about 5 liters of blood in your body. Your heart Biology of the Heart The heart is a hollow organ made of muscle. The heart and blood vessels are part of your cardiovascular system. Your heart pumps blood through your blood vessels Blood carries oxygen and nutrients... read more constantly pumps blood throughout your body.

What does blood do?

Blood is your body's delivery service. Your blood:

  • Carries oxygen, water, and nutrients to all the tissues in your body

  • Collects waste products from your tissues and takes them to be removed

  • Carries cells and proteins that help defend your body from foreign substances

All the cells Cells Often thought of as the smallest unit of a living organism, a cell is made up of many even smaller parts, each with its own function. Human cells vary in size, but all are quite small. Even... read more Cells in your body need oxygen and water to live. Your cells also need nutrients such as sugar, proteins, and fats. Your blood picks up oxygen in your lungs, and water and nutrients from your stomach and intestines.

Your cells create waste products when they process nutrients. Oxygen and nutrients turn into carbon dioxide and the chemical waste products that become part of urine. Your blood carries carbon dioxide to the lungs Overview of the Respiratory System To sustain life, the body must produce sufficient energy. Energy is produced by burning molecules in food, which is done by the process of oxidation (whereby food molecules are combined with... read more , where it is breathed out. Waste products are carried to your kidneys Kidneys The kidneys are bean-shaped organs that figure prominently in the urinary tract. Each is about 4 to 5 inches (12 centimeters) long and weighs about one third of a pound (150 grams). One lies... read more , where they are filtered out of blood and into urine. Your blood carries other waste products to your liver for further processing and removal.

Your immune system Overview of the Immune System The immune system is your body's defense system. It helps protect you from illness and infection. The immune system's job is to attack things that don’t belong in your body, including: Germs... read more is your body's defense system against invaders such as germs and cancer cells. Your blood carries the special cells and proteins of your immune system to where they're needed.

What is in blood?

Blood is made up of:

  • Liquid (plasma)

  • Red blood cells

  • White blood cells

  • Platelets

Red and white blood cells and platelets are constantly being made in your bone marrow, which is inside your bones.

Plasma

Red blood cells

Red blood cells contain a red material called hemoglobin. When blood flows through your lungs, hemoglobin picks up oxygen to go to your tissues. Hemoglobin also carries carbon dioxide back to your lungs so you can breathe it out.

White blood cells

White blood cells are part of your immune system Overview of the Immune System The immune system is your body's defense system. It helps protect you from illness and infection. The immune system's job is to attack things that don’t belong in your body, including: Germs... read more . White blood cells travel through your blood to find and fight foreign substances such as germs and cancer cells. Once they fight a certain substance, white blood cells usually remember it so they can fight it more quickly the next time it appears.

Platelets

What problems can develop in your blood?

Common blood problems usually involve:

  • Having too few or too many red blood cells

  • Having too few or too many white blood cells

  • Having too few or too many platelets

Too few platelets Overview of Low Platelet Count (Thrombocytopenia) Platelets are small cells that circulate in your bloodstream and help your blood clot. They're made in your bone marrow like other blood cells. Platelets are also called thrombocytes. Your blood... read more increases your risk of bleeding after injuries, surgery, or even for no reason at all. Having too many platelets makes it hard for your blood to clot normally. This can cause too much clotting or not enough clotting.

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Kidney Infection
Pyelonephritis is an infection that affects one or both kidneys. Which of the following is the most likely cause of this infection?
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