Regulation of Tissue Perfusion and Exchange of Solutes, Macromolecules, and Water Between Blood Vessels and the Interstitial Space

In this chapter you will learn how the human body regulates the supply of blood and its components to different organs and tissues in such a way that every tissue gets exactly what is needed for its function in different situations. In general, blood supply can be regulated by increasing or decreasing the total cardiac output as well as by locally increasing or decreasing the tissue perfusion. Blood transports substances to the sites where they are needed (e.g., nutrients and oxygen to tissues) or removes substances from tissues for disposal (e.g., uric acid and carbon dioxide). At these sites substances therefore have to cross the vascular barrier to reach the tissue cells or the blood, respectively. In general, this happens at the smallest blood vessels, the capillaries. You will learn how blood supply to these capillaries is locally regulated and by which mechanisms the different blood components can be transported though the vessel wall. You will also see that the described mechanisms may differ between different organs/tissues, and you will be provided with examples on how they can be adapted according to actual needs. Furthermore, you will learn that in some organs, the circulatory system fulfills special functions relevant for the whole organism (e.g., urine formation in the kidney).