Blood carries oxygen and nutrients through your blood vessels to your organs to keep them healthy. Without enough blood, you'll feel sick and might even die.
When you're injured and bleeding, your blood forms a clot to seal damaged blood vessels and stop the bleeding. Blood has special clotting substances and platelets (very small blood cells) in order to make the clot.
A blood clot is a clump of material your blood makes to plug up the bleeding from a cut. Blood clots are made of special clotting substances and platelets (very small blood cells).
White blood cells are part of your body's immune system defenses against infection and cancer. Your body has several types of white blood cells. Most white blood cells are made in your bone marrow.
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 (a little more than 1 gallon) of blood in your body. Your heart constantly pumps blood throughout your body.