Oxygen is consumed to provide energy to cells, leaving carbon dioxide as a waste product, which the red blood cells carry away from the tissues and back to the lungs. There are five main types of white blood cells that work together to provide the body's major mechanisms for fighting infections, including the production of antibodies. Neutrophils, also called granulocytes because they contain enzyme-filled granules, are the most prevalent white blood cell type. They help protect the body against bacterial and fungal infections and ingest foreign debris. Monocytes ingest dead or damaged cells and provide immunologic defenses against many infective organisms.
Eosinophils kill parasites, destroy cancer cells, and are involved in allergic responses.
Basophils also participate in allergic responses. As part of the blood's protective mechanism for stopping bleeding, they gather at a bleeding site, where they are activated. Once activated, they become sticky and clump together to form a plug that helps seal the blood vessel and stop the bleeding. At the same time, they release substances that help promote clotting. Red blood cells tend to flow smoothly through the bloodstream, but white blood cells do not.