Blood is the fluid of life, it’s a liquid connective tissue that carries everything you need to perform the vital functions of your body, but I don’t want to go “por los cerrros de Úbeda”. Today, we’ll talk about its colour, which is the visual perception generated by our brain to different wavelengths inside the visible range of the electromagnetic spectrum.
The blood colour, is usually red and as many people know this is due to the hemogobin, a globular protein present in high concentrations in the erythrocytes. The hemoglobin is formed by four polypeptide chains and each one contains a heme group.
The porphyrin ring (protoporphyrin IX), is inside the protein structure to avoid a fast oxidation, and is attached to a Fe2+ ion, which presents six coordination bonds, where one of them is perpendicular to the site binding the molecular oxygen. When this connection happens, the blood colour is bright red, this blood is flowing through the arteries. When the Fe ion is free from the oxygen, then it binds with the carbon dioxide, and as a result of this blood colour gets a little red and darker and that is the blood that flows through the venous.
Wow! Green blood! Yep, there are several animals like fishes, lizards, worms and I don’t know what more, that have high concentration of biliverdin in blood. Biliverdin is a pigment that comes from the degradation of the heme group in hemoglobin and which confers a greenish colour wherever it is.
In humans, the biliverdin is degraded until it is excreted, although many of you already know the yellow pigment that causes jaundice (accumulation of biliberdin).
There have been cases in which the excessive sulfur compounds intakes (among others), eg. sulfonamides present in some drugs (sumatriptan) makes the blood present a green colour. The cause is that the sulfur atoms bind the hemoglobin (unknown structure), and it seems that the union is so stable that just may disappear with the natural degradation of erytrocites containing the sulfur atoms.
There are animals such as arthropods and mollusks that haven’t blood strictly speaking, but they have a fluid called homolymph similar to blood, which isn’t so efficient at transporting oxygen, but it contains properties that favor tha inmune system. The homolymph has homocytes with high concentrations of a metalloprotein, hemocyanin, whose ion is copper instead of iron.
When this protein is bound to oxygen becomes blue and when it is released it becomes colourless.