Oxygen saturation (medicine)
Oxygen saturation is the fraction of oxygen-saturated hemoglobin relative to total hemoglobin (unsaturated + saturated) in the blood. The human body requires and regulates a very precise and specific balance of oxygen in the blood. Normal blood oxygen levels in humans are considered 95–100 percent. If the level is below 90 percent, it is considered low resulting in hypoxemia. Blood oxygen levels below 80 percent may compromise organ function, such as the brain and heart, and should be promptly addressed. Continued low oxygen levels may lead to respiratory or cardiac arrest. Oxygen therapy may be used to assist in raising blood oxygen levels. Oxygenation occurs when oxygen molecules () enter the tissues of the body. For example, blood is oxygenated in the lungs, where oxygen molecules travel from the air and into the blood. Oxygenation is commonly used to refer to medical oxygen saturation.
Respiratory pigment
A respiratory pigment is a molecule, such as hemoglobin in humans and other vertebrates, that increases the oxygen-carrying capacity of the blood. The four most common invertebrate respiratory pigments are hemoglobin, hemocyanin, hemerythrin and chlorocruorin. Hemoglobin is bright red when oxygenated, and dark red(purplish) when deoxygenated, oxygenated hemocyanin is blue in colour, deoxygenated it is almost colourless. Oxygenated chlorocruorin turns from green to red, whereas oxygenated hemerythrin is a violet to pink colour and colourless when deoxygenated. Any of various coloured conjugated proteins, such as hemoglobin, occur in living organisms and function in oxygen transfer in cellular respiration.