How do red blood cells travel through capillaries?

Red blood cells travel through capillaries in single file due to the narrow diameter of these blood vessels. Capillaries are the smallest and thinnest blood vessels in the circulatory system, with a diameter that is often only slightly larger than that of a single red blood cell. This size constraint forces red blood cells to move individually, allowing them to navigate through the tight spaces effectively.

Traveling in single file ensures that each red blood cell can efficiently exchange gases — oxygen and carbon dioxide — with the surrounding tissues. This one-by-one passage also minimizes the chances of blockage and promotes optimal circulation throughout the body. In contrast, traveling in clusters or groups could hinder this essential function and lead to complications, such as reduced oxygen delivery to tissues or increased resistance within the capillary network.