IS THE COLOR OF YOUR BLOOD BLUE WHEN DE-OXYGENATED?

One of the most common myths about blood every student in their school or elsewhere can hear is “Human blood is Blue in colour when de-oxygenated and it is red when oxygenated”. Some may even prove this theory by the bluish-green colour of the vein in our forehand. Does blood inside our veins (de-oxygenated blood) blue? What is the reason for the bluish-green colour of veins in our forehand?

CONTENTS

• Blood and its Components
• Is the colour of our blood Blue?
• Blue blood of Octopus
• Why are our veins Bluish-green?

BLOOD AND ITS COMPONENTS

Blood is a liquid connective tissue that accounts for nearly 7% to 8% of our body’s total weight. Blood comprises four key components–Plasma, Red Blood Cells, White Blood Cells, and Blood Platelets. Plasma is the fluid component of blood and it is rich in ions, cells that produce antibodies, and forms the base for humoral immunity. White Blood Cells are responsible for cell-based immunity and provide a strong defence against invading germs. Blood platelets are the particles that help in the clotting of blood. Red Blood Cells are responsible for the transport of oxygen throughout the cells in our body.

As we all know, Red blood cells carry Oxygen with the help of a protein called haemoglobin. Haemoglobin is a metalloprotein that has four sub-units containing iron atoms. So, a single haemoglobin protein can bind four oxygen molecules.

The colour of the blood highly depends on the colour of the Red Blood Cells, as they are present in higher concentrations when compared to other blood cells (99.9%).

 

IS THE COLOUR OF OUR BLOOD BLUE?

No. Whether oxygenated or de-oxygenated, the colour of the blood is always red. The thickness or the intensity of the red colour of the blood may vary with the oxygen content. The Red colour of blood is because of Haemoglobin protein–not “oxygenated” haemoglobin. The Haemoglobin protein contains the iron atom. Iron is also responsible for the red colour of the planet “Mars”. The presence of this pigment (whether oxygenated) is sufficient for the red colour of blood.

 

BLUE BLOOD OF OCTOPUS  

So, is the blood in octopus blue? Yes, it is, and it is because of the presence of Hemocyanin pigment. Hemocyanin pigment is rich in copper content. It is initially colourless and when oxidized (Addition of oxygen to Hemocyanin) it turns into blue. We can prove this well with a simple chemistry experiment where oxidation of Cuprous (II) oxide will lead to a colour change from green to blue.

 

Blood of Octopus is Blue due to Hemocyanin

WHY ARE OUR VEINS BLUISH GREEN?

It is based on a simple physics theory—the scattering of light. The white light (the combination of all coloured spectrums) when incident on the nerves containing blood, all the colours get absorbed and the light in the Blue-Green area gets reflected leading to the visualization of bluish-green colour to our naked eye. An in-depth article on the Visualization of colours can be found here

Blood is always red. Don’t let anyone fool you with petty theories. Also, donate blood whenever you can. It won’t cost us much in donating one pint (525 ml) of blood periodically. The continuous reduction in blood donation has led to the rise of artificial blood research which is also described here.

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