Red Blood Cells

Red blood cells are responsible for the transport of oxygen and carbon dioxide. The hemoglobin molecule makes it possible for erythrocytes to carry oxygen. When deoxygenated blood is pumped to the lungs, oxygen diffuses into the bloodstream and binds to hemoglobin. When hemoglobin reaches deoxygenated tissues in the body, it will give up the oxygen molecule. Oxygen then diffuses into cells to be used as the final electron acceptor for cellular respiration.

Cellular respiration produces carbon dioxide. Most carbon dioxide is transferred into the erythrocyte by diffusion, while some carbon dioxide remains in the plasma. Once inside the red blood cell, about half of the CO₂ binds to sites on the hemoglobin molecule. The rest of the carbon dioxide will combine with water to form carbonic acid.

Carbonic acid dissociates into hydrogen ions(H ⁺) and bicarbonate ions (HCO₃ ^-). Bicarbonate ions will diffuse back into the plasma. Hydrogen ions will bind to the hemoglobin molecule and, therefore, not increase the pH of the blood.

CO ₂ + H ₂ O ↔ H ₂ CO ₃ ↔ H ⁺ + HCO ₃ ^-

When red blood cells reach the lungs, the above reaction is reversed. Bicarbonate ions enter the red blood cells and combine with hydrogen ions to form carbonic acid. This is broken down into carbon dioxide and water. Carbon dioxide diffuses out of the red blood cells into the lungs where carbon dioxide is released.

Carbon monoxide (CO) is a chemical produced by incomplete combustion reactions.  The molecule has a high-affinity for hemoglobin and does not readily release.  For this reason, CO can displace oxygen in the blood with potentially fatal results.  As a warning system, carbon monoxide detectors are an important safety technology in the home and workplace.  Most vehicles are equipped with a catalytic converter to eliminate CO from the exhaust.

Anemia is a condition that occurs when there are too few red blood cells or too little hemoglobin inside red blood cells. Oxygen flow is reduced and a person will be tired and appear pale. Anemia can be caused by a lack of iron, which is a key component of hemoglobin. A diet that includes iron-rich foods (such as red meat, leafy greens, and beans) can help alleviate anemia.

Red blood cells are terminally differentiated, which means they can never divide. They have a lifespan of about 120 days. Liver and spleen cells ingest blood cells at the end of their life cycles, and the iron from hemoglobin is reabsorbed into the body. The remaining portion of the blood cells is degraded into bile pigments, which are secreted by the liver.