Why is blood red?

I believe everyone knows that human blood is red when it flows out. If the blood is in the air for a long time, it will turn black because it is oxidized by the air. However, in real life, many people do not know why human blood is red. This requires a detailed understanding of the composition of blood. If you don’t know this knowledge yet, let’s learn about it in detail below.

Why is blood red?

It is common knowledge for many people that human blood is red. But not everyone knows why blood is red. Let’s learn about it today.

Human blood is red because of the red blood cells in the blood. The red blood cells contain hemoglobin. Each hemoglobin molecule is composed of four molecules of globin and four molecules of ferrous heme. Each heme is composed of four pyrrole rings with an iron atom in the center of the ring. So to put it simply, it is because of the iron-containing pyrrole ring in hemoglobin that it appears red.

The iron in hemoglobin is divalent, so it is called ferrous hemoglobin. When it combines with oxygen, its chemical valence remains unchanged to form oxygenated hemoglobin, which is bright red, that is, arterial blood; after dissociating from oxygen, it becomes dark red, that is, venous blood. In the picture below, the left is arterial blood and the right is venous blood.

The blood of humans and most animals in the world is red. But blue blood does exist. The blood of a marine creature called horseshoe crab is blue. This is because the main component of their red blood cells is hemocyanin rather than hemoglobin. This hemocyanin contains copper and is blue-green in color, so it is also called ceruloplasmin.

The pale blue blood flowing in horseshoe crabs contains a high level of copper and will coagulate when it comes into contact with bacteria. Therefore, by utilizing this special reaction of horseshoe crab blood and processing it, a special test reagent - "horseshoe crab reagent" can be made. The horseshoe crab test kit can accurately and quickly detect whether the internal tissues of the human body are diseased due to bacterial infection. It can also be used to monitor toxin contamination in the pharmaceutical and food industries. A reagent is made with horseshoe crab blood and then dripped into the injection solution. If the reagent coagulates or changes color immediately, it means that the injection solution contains bacterial endotoxins that can cause fever, shock, or even death.

So are there blue-blooded people in the world? According to media reports, Vesey, a famous sports physiology expert at the University of California School of Medicine, discovered a race of people with extremely strong adaptability, blue blood and blue skin, at an altitude of more than 6,000 meters on Mount Ocanquircha in Chile. The person on the left in the picture below is a blue-blooded person.

The discovery of the blue race has challenged the traditional theory of racial division: in addition to the four races of yellow, white, black and brown, there should be a blue race. So how did their blue blood and skin come about? Combined with the theory that horseshoe crab blood is blue, people speculate that people with blue blood may have a lack of iron and an excess of copper in their blood.