If Blood Is Red, Why Are Veins Blue?
Hello friend, first I will ask you a question; Have you seen how iron is oxidized? What color do you see? It's red right!
Now, do you know what the main content of the blood is? They are the erythrocytes. Small blood cells responsible for transporting the oxygen we breathe, through the body more specifically through the blood vessels. The erythrocytes transport oxygen thanks to their internal molecules called Hemoglobins responsible for capturing oxygen.
The hemoglobin has an iron atom in the center, which allows this molecule to capture oxygen. When it is united, what we know as oxidation of the blood is produced, this is when the blood acquires the reddish color.
This happens every time the blood passes from the heart to the lungs where the exchange of oxygen is carried out by carbon dioxide. That is, the blood comes with carbon dioxide from the body and excretes it in the lungs, while the oxygen in the lungs enters the blood and oxidizes it.
This red oxidized blood travels through the arteries, arterioles and capillaries; in the latter, another exchange is made (inverse to the previous one). Blood expels oxygen to the organs and the organs transfer the carbon dioxide produced in cellular respiration.
Now the blood is enriched in carbon dioxide and it travels from the capillaries to the veins, collecting all the carbon dioxide and expelling the oxygen inside the body, and with this the reddish coloration. When united with CO2, it loses its red color and turns violet. When mixed with more debris, along with the skin type of the person and the effects of light on it, it resembles a more bluish color.
I hope I have helped in your doubt, happy night