The human body contains about 5 liters of blood.
Blood is a complex fluid that transports oxygen and nutrients to cells and carries away waste products.
The liquid part of blood (plasma) is mostly water, but it also contains dissolved proteins, sugars, salts and other substances.
Blood also has different types of cells:
- Red blood cells (erythrocytes) transport oxygen from the lungs to the rest of the body via their oxygen-binding protein hemoglobin.
- White blood cells (leukocytes) fight infection. They are part of the immune system, which protects the body from foreign substances such as bacteria, viruses and parasites.
- Platelets (thrombocytes) play an important role in the clotting of blood during injury or surgery. These tiny fragments help to stop bleeding by plugging damaged blood vessels until the clotting process can repair the damage.
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