Within the human body we have 60,000 miles of blood vessels. We have three types of cells in the blood, red, white, and platelets. Red blood cells transport oxygen throughout the body while white blood cells help protect us against infection. Platelets are involved in clotting.
When you get a cut your vessels send out signals calling for for platelets and proteins to help in clotting. In addition, white blood cells also come to the rescue. A blood clot is a group of chemicals and cells that work together to stop the flow of blood in a small area.
All blood cells are made within your bone marrow. Stem cells exist inside the marrow and can form into red blood cells, white blood cells, platelets and more stem cells. Leukemia is cancer that relates to abnormal cell production in the bone marrow. One form of treatment involves replacing some of the bone marrow with healthy bone marrow.

Some fun facts about blood:
There is no substitute for blood.
Red blood cells live about 120 days.
Plasma, which is 90 percent water, is a pale yellow mixture of water, proteins and salts.
Thirteen tests are performed on donated blood, 11 are for infectious disease.
94 percent of blood donors are registered voters.
Newborn baby has about one cup of blood in his or her body.