Red Blood Cells and Physiology

Red Blood Cells (RBCs)

• RBCs, also called erythrocytes, carry oxygen
• Hemoglobin, a protein, gives blood its red color
• A healthy adult male has ~5.4 million RBCs/µL of blood; a healthy adult female has ~4.8 million RBCs/µL
• RBCs are biconcave discs, 7-8 µm in diameter, allowing for efficient gas exchange
• RBCs lack a nucleus and other organelles; they cannot reproduce or carry out extensive metabolic activities
• RBCs contain hemoglobin, making up ~33% of their weight; synthesized before nucleus loss
• RBC production rate is high, ~2 million/second, to maintain normal numbers.

RBC Physiology

• RBCs are specialized for oxygen transport
• RBCs lack mitochondria, generating ATP without oxygen, so they don't consume the oxygen they carry
• Their biconcave shape maximizes surface area for gas exchange
• Each RBC contains ~280 million hemoglobin molecules
• Hemoglobin is a protein (globin) with four polypeptide chains (two alpha, two beta) and heme groups; each heme contains iron that reversibly binds oxygen
• Hemoglobin carries 4 oxygen molecules

Hemoglobin Function

• Transports oxygen
• Transports ~23% of carbon dioxide
• The iron in heme binds oxygen for transport by hemoglobin
• Carbon dioxide combines with amino acids in the globin, then released in lungs
• Plays a role in blood flow and blood pressure regulation
• Hemoglobin contains 4 polypeptide chains and 4 heme groups
• Each subunit has a heme ring containing iron, capable of binding 1 oxygen molecule. Therefore hemoglobin can carry 4 oxygen molecules.