What is the role of red blood cells in the human body?

Red blood cells, also known as erythrocytes, primarily function to transport oxygen from the lungs to the tissues and organs throughout the body. Their structure is uniquely adapted for this task; they contain hemoglobin, a protein that binds to oxygen molecules. This binding allows red blood cells to carry a much higher amount of oxygen than would otherwise be possible if it were dissolved in plasma alone.

Additionally, red blood cells play a role in transporting a small amount of carbon dioxide, a metabolic waste product, back to the lungs to be exhaled, but this is not their primary function. The regulation of blood pressure is primarily managed by the vascular system and hormones, while the immune response and fighting infections is managed by white blood cells, not red blood cells.

Thus, the correct answer highlights the essential role of red blood cells in oxygen transportation, which is critical for cellular respiration and energy production in the body. Understanding this function helps to appreciate how the body maintains its vital processes.