Blood is a unique life-saving fluid that supplies the body’s organs and cells with oxygen and nutrients and helps regulate body temperature, fight infections and remove waste (Fox, 2006; Hicks, 2000; Vander et al., 2003). Blood consists of cells suspended in a watery fluid called plasma, which also contains nutrients such as glucose (sugar), lipids (fat), proteins, hormones, clotting agents and other vital molecules.
There are three types of cells in the blood: red blood cells, white blood cells and platelets. Red blood cells carry oxygen from the lungs throughout the body, white blood cells help fight infections, and platelets help with clotting. Platelets also contain numerous growth factors, which may be responsible for healing after an injury.
Plasma makes up approximately 55% of the total volume of blood and the remaining 45% consists of cellular material (e.g. red blood cells, white blood cells and platelets). The average adult holds between 4 and 6 liters of blood in his or her body (Brooks, 2000; Vos, 2006; Hicks, 2000; Vander et al., 2003).
Transport of blood
Blood transports oxygen to all body tissues and transports waste products to other parts of the body (Fox, 2006; Hicks, 2000; Vander et al., 2003). Blood also stores, protects and transports hormones to parts of the body where they exert their effects.
In addition, blood transports nutrients from the gastrointestinal tract to various organs and tissues throughout the body (Fox, 2006; Hicks, 2000; Vander et al., 2003). Last but not least, the blood transports and stores cells that help the body heal when it is injured, such as stem cells (Villaron et al., 2004).
Regulation
Blood helps regulate body temperature by transferring heat to and from the internal core and periphery of the body as it circulates. When the blood comes close to the skin, it can be heated or cooled depending on the external environment (Brooks, 2000; Vos, 2006; Tortora, 2008; Vander et al., 2003). If the external environment is colder than circulating blood, body heat is lost and vice versa.
Blood is also essential in regulating pH levels (acid balance) in the body and maintaining the water content of body cells (Tortora, 2008). With regard to pH levels, blood is just one of many buffer systems used by the body to maintain a normal range. Other systems that help manage the body’s pH levels are the respiratory and renal (kidney/urinary) systems.
Protection
Blood provides protection against excessive blood loss through the clotting mechanism (e.g. platelets), which seals damaged tissue and forms a scar (Fox, 2006; Hicks, 2000; Vander et al., 2003). It also provides specialized immune cells to fight against foreign toxins in the body, helping to reduce the risk of disease and illness (Brooks, 2000; Vos, 2006; Hicks, 2000; Vander et al., 2003).