Blood bulky muscular legs. In insects, the blood (more properly called hemolymph) is not involved in the transport of oxygen. (Openings called tracheae allow oxygen from the air to diffuse directly to the tissues.) Insect blood moves nutrients to the tissues and removes waste products in an open system. Other invertebrates use respiratory proteins to increase the oxygen-carrying capacity. Hemoglobin is the most common respiratory protein found in nature. Hemocyanin (blue) contains copper and is found in crustaceans and mollusks. It is thought that tunicates (sea squirts) might use vanabins (proteins containing vanadium) for respiratory pigment (bright-green, blue, or orange). In
Packed red blood cells used to restore oxygen-carrying capacity in people with anemia due to trauma or other medical problems, and are by far the most common blood component used in transfusion medicine. Historically they were transfused as part of whole blood, but are now typically used separately as RBCs and plasma components. The process of identifying a compatible blood product for transfusion is complicated. Side effects can include allergic reactions including anaphylaxis, red blood cell breakdown, fluid overload, infection, and lung injury. Giving incompatible RBCs to a person can be fatal. With current testing methods in high-income countries the risk of infection is