Is it true that blood is blue when not exposed?

The claim that blood is blue when not exposed is a common misconception. In reality, blood is never blue inside the body, regardless of whether or not it is exposed to oxygen.

Here's why:

1. Hemoglobin and Oxygen:

The red colour of blood is due to the presence of a protein called hemoglobin, which carries oxygen throughout the body. Hemoglobin contains an iron ion, which binds to oxygen molecules. When blood is oxygenated (carrying oxygen from the lungs to the rest of the body), the iron ion in hemoglobin is bound to oxygen and appears bright red.

2. Deoxygenated Blood :

When blood is deoxygenated (carrying carbon dioxide from the body's tissues back to the lungs), the iron ion in hemoglobin is not bound to oxygen and has a darker, more purplish red appearance. However, it is still not blue.

The misconception about blood appearing blue when deoxygenated may have arisen because veins, which carry deoxygenated blood, often appear blueish under the skin. This is due to the way light interacts with tissues and blood vessels, not because the blood itself is blue.

In summary, blood is never truly blue inside the body, regardless of its oxygenation state. The bright red colour of oxygenated blood and darker red colour of deoxygenated blood are due to the properties of hemoglobin and the way it interacts with oxygen.