What is blood?

Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the circulatory system is also known as peripheral blood, and the blood cells it carries, peripheral blood cells. Blood contains specialized cells that serve particular functions. These cells are suspended in a liquid matrix known as plasma. Blood is both a tissue and a fluid. It is a tissue because it is a collection of similarly specialized cells that serve particular functions. If blood flow ceases, death will occur within minutes because of the effects of an unfavorable environment on highly susceptible cells.