Cells in an organism depend on a continuous supply of oxygen to produce the energy needed to perform their myriad functions, so that the regulation of tissue oxygenation is a key activity of any organism. This regulation involves the coordinated action of the cardiovascular and respiratory systems, as well as the blood which carries the oxygen to the vicinity of cells. The utilization of oxygen is a local phenomenon, with each cell having its own specific needs which can change over time according to the current activity of the cell. Because of the local nature of oxygen utilization, the integration and matching of oxygen supply to oxygen demand take place in the microcirculation. An overall summary of the diffusional interactions among different vessels in the microcirculation is shown in Figure 17.

FIGURE 17

Pathways for oxygen diffusion in microvascular networks. Whereas Krogh considered oxygen diffusion from capillaries to the tissue (lower left of figure), current knowledge about oxygen diffusion in the microcirculation shows that oxygen can diffuse between (more...)

Altered demand for oxygen is sensed in various ways and is communicated to the terminal vasculature which responds by changing blood flow in a way that satisfies the oxygen demand. An imbalance between oxygen supply and oxygen demand is a hallmark of a number of (patho)physiological conditions, such as aging, exercise, hemorrhage, sepsis, diabetes, anemia and heart failure. As our understanding of oxygen transport increases, based on modern techniques of measuring oxygen, it can be anticipated that new therapeutic interventions that increase the oxygen supply (e.g., artificial oxygen carriers) or reduce oxygen demand (e.g., inhibition of tissue metabolism) will become available to aid in the regulation of tissue oxygenation.