oxygentransport

Oxygentransport refers to the physiological process by which oxygen is moved from the external environment to cells throughout the body. In air-breathing animals, oxygen is inhaled into the lungs, where it diffuses across the respiratory surface into the bloodstream. It binds to hemoglobin in red blood cells for transport and is released in tissues where metabolic demand is highest, creating a diffusion gradient that sustains aerobic respiration.

Hemoglobin is a tetrameric protein with four heme groups capable of binding one oxygen molecule each. Binding is cooperative, so loading in the lungs increases affinity and unloading in tissues is favored as conditions change. In humans, oxygenated hemoglobin (oxyhemoglobin) carries most circulating O2, while deoxygenated hemoglobin releases oxygen to tissues. The affinity of hemoglobin for O2 is modulated by factors such as pH, carbon dioxide, temperature, and 2,3-bisphosphoglycerate.

Most oxygen is transported bound to hemoglobin; only a small fraction dissolves in plasma. The amount of O2 carried depends on hemoglobin concentration and its saturation, described by the oxygen dissociation curve. Arterial PO2 is typically around 100 mmHg, while venous PO2 is lower, reflecting tissue uptake. Diffusion gradients from capillaries into cells underlie final oxygen delivery.

Other oxygen carriers include myoglobin in muscle and fetal hemoglobin, which has a higher affinity for oxygen. Clinically, disturbances in oxygentransport can result from anemia, abnormal hemoglobins, or respiratory or circulatory failure, emphasizing the system's integration with ventilation, circulation, and cellular metabolism.