Red blood cells

Red blood cells, also called erythrocytes, are the most common component of blood (40-45% of the blood) and the smallest whole cells (6-9 µm). Typically, adults have around 20-30x10¹² red blood cells circulating in their body. , forty to forty-five percent of the blood, and the smallest whole cells, six to nine micrometers. Typically, adults have around twenty to thirty times ten to the twelve red blood cells circulating in their body.

Red blood cells lack a nucleus (they are anucleate) so they can be packed full of the iron-containing protein, Hemoglobin. This molecule binds to oxygen in the lungs so that it can be transported around the body and delivered to the tissues and organs. Hemoglobin also binds to carbon dioxide so that red blood cells can transport it from cells in the body back to the lungs, where the waste gas is exhaled.

Red blood cells are biconcave or discoid in shape, meaning that they have a thicker outer edge and narrower center (see Figure 1). This shape increases the cells’ surface area for gas exchange and also makes the cells flexible enough to flow through even the smallest of capillaries.

Figure 1: Red blood cells (RBCs)