The Chemistry of Blood Colours

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Blood is a necessary component of the majority of living organisms (all vertebrates and some invertebrates); it carries vital nutrients, oxygen and proteins to body tissues and carries away waste products. Blood, although most commonly red, can also be found in such colours as green, blue, clear, pink and violet. However, the common misconception surrounding the idea that human blood is blue before oxygenation is false. All human blood is varying shades of red; these wild alternate colours are found in other animal species such as certain species of crabs and insects. This colouring of the blood can be seen as an indicator of oxygen carrying ability or make apparent the metal with the highest concentration in the blood.

The colour containing portions of blood are known as respiratory pigments; these pigments are metal containing proteins which combine reversibly with oxygen. Respiratory pigments are found within cells of blood and their primary function is to aid in the transportation of molecular oxygen. There are four unanimously recognised respiratory pigments, these are; hemoglobin, followed by hemocyanin, then chlorocruorin and Hemerythrin. These four pigments occur in greater percentages and are far more efficient in carrying oxygen than the few other pigments known. These lesser known pigments (not all fully recognised as respiratory pigments) include; vanadium chromagen and pinnaglobin.

Haemoglobin, the most common respiratory pigment on earth is the pigment found in all vertebrates (excluding a few Antarctic fish) including humans. Hemoglobin is located within the platelet component of blood giving the distinctive red colouring associated with blood both when oxygenated and deoxygenated, when oxygenated it is a bright red and by the time it is traveling In the veins back to the heart, blood containing haemoglobin is a dark red in colour. This colour is due to the presence of iron in the haemoglobin. Iron is the central atom of the heme group (...
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