Blood circulates in the body through a network of vessels to provide individual cells with oxygen and nutrients as well as to dispose of metabolic wastes. The heart pumps the blood through the lungs where it gets oxygen rich and disposes of carbon dioxide. Blood consists of about 45% solids (cells) and 55% fluids (plasma) which is largely water containing proteins, nutrients, antibodies, hormones and dissolved waste products.

Blood cells are categorized into three types, all of which are formed in a process called hematopoiesis:

 Platelets control blood clotting
 Red blood cells (RBCs) carry oxygen to the body
 White blood cells (WBCs) protect against infection.
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[wptabtitle]Circulatory System[/wptabtitle]
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[wptabtitle]Marrow Production in the Body[/wptabtitle]
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[wptabtitle]What is Blood?[/wptabtitle]
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[wptabtitle]Blood Clotting[/wptabtitle]
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Functions of the blood circulation system:

 Circulates OXYGEN and removes Carbon Dioxide.
  Provides cells with NUTRIENTS.
  Removes the waste products of the metabolism to the excretory organs for disposal.
  Protects the body against disease and infection.
  Clotting stops bleeding after injury .
  Transports HORMONES to target cells and organs.
  Helps regulate body temperature.