Physician Horace Smith describes the importance of human blood:

Each drop of human blood contains over 5 million red cells … In an average lifetime, a person's red cells arranged in single file would reach from the earth to the sun and back five times!

Our bodies contain approximately 60,000 miles of blood vessels … Through this delivery system, blood provides everything our cells need to live, and they take away waste that would poison us. At the cellular level, capillaries are so small that they are about the size of a single red blood cell … To connect with all the cells in the body, capillary walls cover an area of about 70,000 square feet … The circulatory system is the epitome of consistency. Every day, the heart beats 100,000 times, and over an average lifespan, this amazing machine beats 2.5 billion times, pumping 60 million gallons of blood. During this time, the heart never takes time off. We can't afford for it to take a break—even a few minutes without blood supply causes severe brain damage or death. Virtually all other cells in the human body are stationary, but blood is mobile tissue, carrying nutrients to every part of the body … protecting us from harm and healing our wounds.

No wonder the Old Testament says that "The life of every creature is its blood" (Lev. 17:14). Today, we understand the significance of this truth even more deeply. There are no cells in the human body that can live without continual contact with life-giving blood. Every type of cell, from the ones that survive only moments to those that live for many years, owes its life to the flow of blood. All three types of cells in human blood—red cells, white cells, and platelets—perform functions that are essential to life.