What is blood?

The word “erythrocyte” comes from the Greek words erythros (red) and zytos (cell). Erythrocytes give blood its red colour. Normally disc-shaped, red blood cells (or red cells) can change their shape substantially to pass through narrow blood vessels. Mature erythrocytes do not have a nucleus. They are available to the body for around 100 to 120 days to transport oxygen and are then broken down in the spleen.

Erythrocytes contain haemoglobin, which is what enables them to bind oxygen. Certain stress factors and diseases (heavy smoking, diabetes) can cause red cells to lose their ability to change shape. If this happens, the blood circulation is impaired, vessels become clogged and tissues may die.

Leukocytes also get their name from the Greek language (leukos = white). These colourless blood cells are called “white blood cells” due to the white paste they form when separated from other blood cells.

Technically speaking, “white blood cell” is an umbrella term rather than one specific type of cell. There are in fact three sub-groups of white blood cells:

Granulocytes become active when an infection or inflammation appears. Monocytes (or macrophages) are large cells that engulf and digest pathogens or dead cells. Lymphocytes, the heart of the immune system, fulfil two key functions: they make antibodies that attack potential threats and they remember the pathogens involved in previous infections, thanks to a memory that allows them to do so.

Platelets are disc-shaped in structure, like red cells, and their job is to ensure that the blood remains inside the blood vessels. When a blood vessel is even slightly injured, thrombocytes will immediately clump together to seal the tear. A clot of platelets is called a thrombus. These blood clots must not grow too large, or they could block the blood vessel.

Plasma is the liquid part of the blood. Without it, there would be no way for the (solid) blood cells to be transported around the body. In addition to water (90 percent) and salts, plasma contains lipids, hormones and proteins.

Albumin is the most abundant protein in plasma, where it accounts for 60% of total protein content. It prevents the blood from losing too much water and becoming too thick while it circulates through the narrow, permeable blood vessels. Albumin also transports various blood components and nutrients.