Hemoglobin: Structure, Oxygen Transport, and Carbon Dioxide Carriage

Hemoglobin (Hb) is the iron-containing protein in red blood cells that transports respiratory gases.

Structure

Tetramer: 2 α-globin + 2 β-globin chains, each with a heme group (Fe²⁺). Each Hb binds 4 O₂ molecules.

Oxygen Transport

1. In pulmonary capillaries: High PO₂, high pH, low PCO₂ → Hb binds O₂ cooperatively (sigmoid curve).
2. In tissues: Low PO₂, low pH, high PCO₂, high 2,3-BPG → Hb releases O₂ (Bohr effect).

CO₂ Transport

• ~10% as carbaminohemoglobin (Hb-CO₂)
• ~70% as bicarbonate (HCO₃⁻) via carbonic anhydrase
• ~20% dissolved in plasma

Clinical Relevance

• Anemia: Low Hb → reduced O₂ delivery
• Hb variants: HbS (sickle), HbC, thalassemias
• Glycated Hb (HbA1c): 3-month glucose average