Hapenkulku

Hapenkulku is a Finnish term that refers to the transport of oxygen from the lungs to tissues, a core part of respiration and cellular metabolism. The process encompasses pulmonary uptake of oxygen, its transport through the circulatory system, and its release for cellular use. Oxygen must be available for mitochondrial respiration, and hapenkulku components can be studied as ventilation, diffusion, perfusion, and the blood’s oxygen-carrying capacity.

Mechanism: In the lungs, oxygen diffuses across the alveolar-capillary membrane following the alveolar-arterial partial pressure gradient. A portion dissolves in plasma, but most binds to hemoglobin in red blood cells, forming oxyhemoglobin. The oxygen-hemoglobin dissociation curve governs loading in the lungs and unloading in tissues; factors such as pH, CO2, temperature, and 2,3-bisphosphoglycerate shift the affinity through the Bohr effect. Myoglobin in muscles provides a reservoir near mitochondria.

Delivery and consumption: Arterial oxygen content CaO2, determined by dissolved oxygen and Hb-bound oxygen, combined with cardiac output, yields oxygen delivery (DO2). Venous oxygen content CvO2 reflects tissue extraction; oxygen consumption VO2 equals CO × (CaO2 − CvO2). The arterial-venous difference correlates with metabolic activity and can be altered in disease.

Clinical relevance: Disorders that impair hapenkulku include anemia, pulmonary diseases reducing diffusion or ventilation, cardiac failure reducing perfusion, and toxins such as carbon monoxide that decrease effective hemoglobin oxygen-carrying capacity. Management aims to optimize oxygen delivery through supplemental oxygen, transfusion, or treating underlying disorders.

See also: Hemoglobin, Oxygen dissociation curve, Hypoxemia, Oxygen therapy.