What are the functions of blood?

Blood is a vital fluid that performs many important functions in the body. Some of the primary functions of blood include:

1. Transportation: Blood delivers oxygen and nutrients to the cells, and removes wastes from them. Nutrients from the foods you eat are absorbed in the digestive tract and travel in the bloodstream directly to the liver, where they are processed and released back into the bloodstream for delivery to body cells. Oxygen from the air you breathe diffuses into the blood, which moves from the lungs to the heart, which then pumps it to the rest of the body. Blood also picks up cellular wastes and byproducts, and transports them to various organs for removal.

2. Defense: Many types of white blood cells (WBCs) protect the body from external threats, such as disease-causing bacteria that have entered the bloodstream in a wound. Other WBCs seek out and destroy internal threats, such as cells with mutated DNA that could multiply to become cancerous, or body cells infected with viruses. When damage to the vessels results in bleeding, blood platelets and certain proteins dissolved in the plasma interact to create clots that block the ruptured areas of the blood vessels involved. This protects the body from further blood loss.

3. Maintenance of Homeostasis: Blood helps regulate body temperature by absorbing and distributing heat throughout the body. It helps maintain homeostasis through the release or conservation of warmth. Blood vessels expand and contract when they react to outside organisms, such as bacteria, and to internal hormone and chemical changes. These actions move blood and heat closer to or farther from the skin surface, where heat is lost.