Erythrocytes are defined as which?

• A. Red blood cells that transport oxygen
• B. White blood cells that fight infection
• C. Platelets that help clotting
• D. Plasma proteins that carry hormones

Answer: (A)

Erythrocytes are the red blood cells whose main job is to carry oxygen from the lungs to tissues throughout the body, using hemoglobin to bind and release oxygen as needed. The biconcave shape and, in mammals, absence of a nucleus maximize surface area for gas exchange and allow flexible movement through tiny vessels. They also help remove some carbon dioxide by transporting it back to the lungs. This function is distinct from white blood cells (which fight infection), platelets (which aid clotting), or plasma proteins (which carry hormones and other substances). In clinical practice, evaluating erythrocytes through measures like hematocrit/PCV and blood smears helps diagnose conditions such as anemia or dehydration, reflecting the essential role of these cells in oxygen transport.