Why do red blood cells look red?

How the blood gets its red color

How the blood gets its red color

If it stops flowing, we are dead. Blood is life, because blood connects. In this episode of our “From head to toe” series, we explain why it is so thick and red.

If it stops flowing, we are dead. Blood is life, because blood connects. In this episode of our “From head to toe” series, we explain why it is so thick and red.

Blood cells are disposable. Red blood cells, for example, only live 120 days, then they are disposed of in the spleen. They come from the bone marrow, and in abundance. Every day around 200 billion red and 150 billion white blood cells leave the production facility there. They produce stem cells that are able to produce any blood cell type based on a needs analysis. Messenger substances from the different regions of the body signal what they need: red blood cells, white blood cells and platelets that monitor the body. Blood is so vital because our body functions extremely based on the division of labor. No organ can survive on its own, each must be supplied with certain substances. Conversely, waste must be transported away. With the blood, oxygen from the lungs and nutrients from the gastrointestinal tract swim into the tissues, along with hormones and other messenger substances that regulate our body processes. Finally, defense cells that can be mobilized against foreign bodies. Because the body is an open system. But let's stick with oxygen. It provides the energy that the body needs. Maintaining body heat alone requires a continuously glowing inner furnace. Oxygen could also be transported in water, but this would by no means be sufficient to meet the energy demand. So nature came up with something. It is called hemoglobin, is red and gives the blood its color. And it helps keep blood thick.

Hemoglobin contains iron, it soaks up oxygen like a sponge and carries it with it. However, it would be toxic to the body, which is why the red blood pigment is packed inside the red blood cells or erythrocytes. Every microliter of blood contains several million such blood cells. A microliter is a millionth of a liter, which corresponds to a cube with a side length of one millimeter.

The walls of the red blood cells are permeable to gaseous substances such as oxygen. Inside there are around 300 million (!) Hemoglobin molecules per erythrocyte, each consisting of four subunits. They can each form an oxygen molecule via an iron atom. Here, too, supply and demand rule. In the lungs, where there is excess oxygen, it is absorbed by hemoglobin. As soon as the oxygen concentration drops, which is the case in the muscles, for example, the bond is loosened and the oxygen is released again.