What is the primary function of erythrocytes (red blood cells) in the human body?

• A. Regulate blood pressure by secreting hormones that control vasoconstriction
• B. Provide adaptive immune defense by producing antibodies
• C. Transport oxygen (and some carbon dioxide) between the lungs and body tissues
• D. Initiate blood clotting by forming a platelet plug at sites of vascular injury

Answer: (C)

Verified step by step guidance

1. Understand that erythrocytes, or red blood cells, have a specialized structure that supports their main function. They contain hemoglobin, a protein that binds oxygen molecules.
2. Recognize that the primary role of erythrocytes is related to gas transport, specifically carrying oxygen from the lungs to body tissues and returning some carbon dioxide from tissues back to the lungs.
3. Eliminate options that describe functions not associated with erythrocytes: regulating blood pressure (a function of hormones and vascular cells), producing antibodies (a function of certain white blood cells), and initiating blood clotting (a function of platelets).
4. Recall that the biconcave shape of erythrocytes increases their surface area, optimizing oxygen exchange efficiency, which supports their role in oxygen transport.
5. Conclude that the primary function of erythrocytes is to transport oxygen (and some carbon dioxide) between the lungs and body tissues, facilitating cellular respiration and maintaining homeostasis.