Red blood cells (RBC), also known as erythrocytes, are the smallest cells in our bodies. They are only eight thousandths of a millimetre (0.008 mm) in diameter. If all of the red blood cells of the human body were assembled into a chain, it would be approximately 200,000 kilometers long. Red blood cells have a biconcave shape which resembles a flattened disc. They are also adaptable, kind of like bean bags. Due to their structure, red blood cells are able to pass through even the narrowest capillaries.

Due to their flattened disc shape, the area of a red blood cell is one-third larger than that of a circular cell of the same size. Their lifespan is about four months. When they are no longer able to maintain their biconcave shape, the liver and the spleen remove them from the bloodstream. Two to three million new red blood cells are generated in bone marrow every second.

​