gassetransport

Gas transport is the physiological process by which oxygen and carbon dioxide are carried between the lungs and tissues through the circulatory system. It links the respiratory gas exchange that occurs in the lungs with the delivery of oxygen to cells and the removal of carbon dioxide from metabolism.

Oxygen transport: Most oxygen is bound to hemoglobin in red blood cells, though a small portion is dissolved in plasma. Hemoglobin picks up oxygen in the lungs where the partial pressure of oxygen is high and releases it in tissues where it is needed and partial pressure is low. The affinity of hemoglobin for oxygen is modulated by factors such as pH, carbon dioxide levels, temperature, and 2,3-bisphosphoglycerate, which shift the hemoglobin-oxygen dissociation curve and affect loading and unloading.

Carbon dioxide transport: CO2 is carried in blood in several forms. Dissolved CO2 accounts for a portion of transport, and most CO2 is converted to bicarbonate ions (HCO3-) in red blood cells via carbonic anhydrase and released into plasma. CO2 also binds to amino groups on hemoglobin (carbaminohemoglobin). The bicarbonate route is the dominant form of CO2 transport, and the chloride shift helps maintain electrochemical balance as bicarbonate moves out of red blood cells.

Regulation and adaptation: The Bohr effect describes reduced hemoglobin affinity for oxygen with higher acidity and higher CO2, promoting tissue oxygen unloading. The Haldane effect describes changes in CO2 carriage with oxygenation state. 2,3-BPG levels can adjust oxygen affinity and are influenced by altitude and chronic hypoxia.

Clinical relevance: Conditions such as anemia, polycythemia, carbon monoxide poisoning, and pulmonary diseases can impair gas transport. Understanding gas transport is also important in contexts like exercise physiology and critical care.