In human physiology, what is the primary purpose of red blood cells (erythrocytes)?

• A. Transport oxygen (and some carbon dioxide) between the lungs and body tissues
• B. Provide immune defense by producing antibodies and engulfing pathogens
• C. Regulate blood pressure by releasing hormones into the bloodstream
• D. Initiate blood clotting by forming platelet plugs

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the main function of red blood cells (erythrocytes) in human physiology. Red blood cells are specialized cells primarily involved in gas transport within the circulatory system.
2. Step 2: Recall that red blood cells contain hemoglobin, a protein that binds oxygen molecules in the lungs and carries them to body tissues where oxygen is released for cellular use.
3. Step 3: Recognize that red blood cells also assist in transporting a small portion of carbon dioxide, a waste product of metabolism, from the tissues back to the lungs for exhalation.
4. Step 4: Differentiate the functions of other blood components: immune defense is mainly performed by white blood cells, blood pressure regulation involves hormones like renin and angiotensin, and blood clotting is initiated by platelets.
5. Step 5: Conclude that the primary purpose of red blood cells is to transport oxygen (and some carbon dioxide) between the lungs and body tissues, which is essential for maintaining cellular respiration and overall metabolic function.