Fig. 1.

Impact of infection on nutrient homeostasis. Infection can impact the regulation of systemic homeostasis in several ways. A Values of various parameters in the blood are maintained between threshold values. If blood values are outside of this homeostatic bandwidth, corrective action is undertaken. One way by which the immune system can mediate sickness metabolism following infection is by altering these threshold values. B Blood parameter homeostasis is regulated through a dynamic balance between the influx and efflux of nutrients. In this figure, blood glucose is given as an example. Infection can alter this balance in several ways. If threshold values are not altered, changes in nutrient flux are possible only if they are compensated for by equal and opposite alterations in other organs involved in maintaining homeostasis. In this example, reduced glucose uptake by skeletal muscle is compensated for by an increased flux of glucose to the immune system. C Changes in homeostatic regulation negatively impact normal organ function and are therefore not without risk. Strategies with a greater impact, such as changes in threshold levels, are therefore justified only if the risk of serious damage by the pathogen is high. Threats of a lower danger level will therefore have less impact on homeostasis, for example, by altering nutrient flux toward a single organ. Made with biorender.com