During the red blood cell functional lifetime, how do they travel through the circulatory system?

Red blood cells (RBCs) have a critical role in transporting oxygen from the lungs to the tissues and returning carbon dioxide from the tissues back to the lungs. Throughout their functional lifetime, which averages about 120 days, red blood cells navigate the entire circulatory system.

This includes traveling through arteries, where they are propelled away from the heart. From the arteries, RBCs move into arterioles and then capillaries, which are the smallest blood vessels where the exchange of oxygen, carbon dioxide, and nutrients occurs with surrounding tissues. After passing through the capillaries, red blood cells enter venules and then veins, ultimately returning them back to the heart.

Their journey involves a continuous flow through all types of blood vessels—arteries, capillaries, and veins—enabling them to perform their function effectively. This constant circulation is essential for maintaining homeostasis in the body, ensuring that tissues receive adequate oxygen and waste products are efficiently removed. Thus, the correct answer reflects the comprehensive nature of their travel throughout the entire circulatory system.