Other WBCs seek out and destroy internal threats, such as cells with mutated DNA that could multiply to become cancerous, or body cells infected with viruses. Many types of WBCs protect the body from external threats, such as disease-causing bacteria that have entered the bloodstream in a wound. For instance, blood moves carbon dioxide to the lungs for exhalation from the body, and various waste products are transported to the kidneys and liver for excretion from the body in the form of urine or bile. Blood also picks up cellular wastes and byproducts, and transports them to various organs for removal. Moreover, endocrine glands scattered throughout the body release hormones into the bloodstream, which carries them to distant target cells. Oxygen from the air you breathe diffuses into the blood, which moves from the lungs to the heart, which then pumps it to the rest of the body. Most of these travel in the bloodstream directly to the liver, where they are processed and released back into the bloodstream for delivery to body cells. Nutrients from the foods you eat are absorbed in the digestive tract.

The specific functions of blood also include defense, and maintenance of homeostasis, such as distributing heat where it is needed. The primary function of blood is to deliver oxygen and nutrients to, and remove wastes from, the body cells but that is only the beginning of the story. This fluid, which is mostly water, suspends the formed elements and enables them to circulate throughout the body within the cardiovascular system. The extracellular matrix, called plasma, makes blood unique among connective tissues because it is fluid. The cellular elements-referred to as the formed elements-include red blood cells (RBCs), white blood cells (WBCs), and cell fragments called platelets. Like all connective tissues, it is made up of cellular elements and an extracellular matrix. Recall that blood is a connective tissue. Name the fluid component of blood and the three major types of formed elements, and identify their relative proportions in a blood sample.Identify the primary proteins and other solutes present in blood plasma.Identify the primary functions of blood in transportation, defense, and maintenance of homeostasis.Identify the primary functions of blood, its fluid and cellular components, and its characteristics By the end of this section, you will be able to:

Blood plasma viscosity