Capillaries and the Nobel Prize (1916–1922)

Abstract

Krogh’s interest in capillaries was a natural consequence of his interest in oxygen and metabolism. Essential for energy production, oxygen must reach all living cells. He knew that it diffuses across the lung epithelium and becomes bound to hemoglobin in the blood in the lung capillaries. The oxygen-saturated blood reaches the organs and muscles via the capillaries, which branch out among all cells. As Bohr, Hasselbalch, and Krogh had shown, addition of CO₂ to blood lowers hemoglobin’s affinity for oxygen, thus releasing oxygen to the cells where CO₂ is produced. While he was pretty sure that oxygen reaches the cells by diffusion from the capillaries, he did not know how this process could be regulated so as to adequately meet the demand of muscles during heavy work as well as at rest.

It seemed to me clear that there might be some mechanism regulating the conditions of supply [of oxygen]. With constant conditions the facilities for transport must either be ridiculously out of proportion to the requirements of the muscles during rest or ridiculously inadequate to meet their needs during heavy work.