What is the primary function of red blood cells in the cardiovascular system?

The primary function of red blood cells, also known as erythrocytes, is to transport oxygen from the lungs to the tissues and organs throughout the body and to carry carbon dioxide, a metabolic waste product, from the tissues back to the lungs for exhalation. This dual role of oxygen delivery and carbon dioxide removal is critical for maintaining cellular respiration and overall metabolic processes in the body.

Red blood cells contain hemoglobin, a protein that binds to oxygen in the lungs. When blood passes through the pulmonary capillaries, oxygen molecules attach to hemoglobin, forming oxyhemoglobin. As red blood cells circulate through the body's capillaries, hemoglobin releases oxygen to the cells, which is then used for energy production.

Additionally, red blood cells help transport carbon dioxide, which is produced by cells as they metabolize nutrients. Carbon dioxide binds to hemoglobin or is dissolved in the plasma as bicarbonate ions, which helps facilitate its transport back to the lungs for removal from the body.

This function is distinct from the roles of other options: nutrients are carried by plasma components and specialized transport proteins, blood pressure regulation involves a complex interplay of various factors including the autonomic nervous system and the kidneys, and the immune response, particularly fighting infections,