The Basics of Blood


Madeleine Rauh, Dedicated Writer


Have you ever wondered “Man! What is going on inside my body?!”?

Well, the truth is, what’s going on inside the body varies between humans and animals. Humans normally have red blood. Blood may seem disgusting coming from the interior of us but really, it’s the best transportation system for nutrients, minerals, bacteria, viruses, and so much more!

What Makes Blood Red?

Humans have a complex protein molecule in their red blood cells called hemoglobin, and hemoglobin has iron in it. When this iron reacts with the oxygen that we breathe in, it creates the color red. This is a crazy idea since when someone looks at a vein, the blood appears blue. That vein appears blue because it’s simply an illusion.

In the color wheel, colors mix to make different colors. This color mixing applies with the color someone sees a vein as. According to Medical News Today, “Arteries transport blood that is rich in oxygen away from the heart to be used by organs and tissues in the body. The veins return deoxygenated blood to the heart. It is a common myth that veins are blue because they carry deoxygenated blood.”

Blood in the human body is red no matter how much oxygen there is, although the shade of red may vary. The amount of oxygen in the blood determines the shade of red. As blood leaves the heart and is oxygen-rich, it is a bright red color. When the blood returns to the heart, it has less oxygen. It is still red but the color will be darker. This darker red appears blue through the skin  because of how light travels through it. A vein is actually a pinkish-whitish color, and blood is a dark-red color. When both these colors are mixed with skin, it creates the illusion of the vein being blue. Although, this is mainly based on how an eye perceives light.

So Then, What is Blood?

As we all know, blood is in our bodies (obviously). So how much is in our body? Well, the exact amount of blood, can’t be told. What is speakable is the amount of blood in a body depends on the size of the body. According to Medical News Today, “Approximately 7–8 percent of a person’s total weight is blood. That means an average-sized woman has about 9 pints of blood and an average-sized man about 12 pints.” Say someone is doing a handstand, their face will turn red because all of the blood is rushing to the head. When a person loses too much blood, it can lead to hemorrhagic shock which is life-threatening. The symptoms of hemorrhagic shock are dizziness, confusion, and low blood pressure. Everyone’s blood contains red blood cells, white blood cells, plasma, and platelets. There are different types of blood types. The most common blood type in the world is type O. There are also type A and type B.

Humans, Animals… Not Always Alike

Some animals though, like snails, octopus, and spiders, do have blue blood. In these types of animals, they don’t use hemoglobin to carry oxygen around the body, they use a compound similar to this called hemocyanin. Unlike hemoglobin which has iron in it, hemocyanin has a copper atom; not an iron atom. The copper atom binds oxygen. According to McGill from Medical News Today, “Unlike mammals, snails, spiders and octopi do not use hemoglobin to transport oxygen but rely on a related compound known as hemocyanin. This molecule, instead of having an atom of iron in its middle, has an atom of copper that binds oxygen. Hemocyanin absorbs all colors except blue which it reflects, making their blood appear blue.” Hemoglobin absorbs every color except red, therefore it reflects red. Although hemocyanin absorbs every color except blue, therefore it reflects blue. When someone says blue blood, they’re usually referring to royal blood. But in science we refer to it as animals with hemocyanin in their blood.


When it comes to the human body, scientists are discovering new things every day. When someone looks at themself in the mirror there are probably a million different things that they wonder about every day. Although, this must be kept in mind: things aren’t always what they seem. No one can ever be sure of something until they are educated on the subject.