The Blood Buffering Systems

Abstract

The six litres (1) of blood in the circulation is in contact with the cytoplasm of the tissues indirectly via the much larger volume (30 1 approximately) of extracellular fluid, which bathes the cells. The blood not only supplies the tissues with nutrients and oxygen, but also receives metabolites and waste products, including CO₂, from them. Thus, the maintenance of homeostasis in the tissues is dependent upon control of the composition of blood between narrow limits. This is achieved by the lungs, which remove CO₂ from the blood, while the kidneys control the HCO ⁻₃ and other ion concentrations and the pH of the blood. The kidneys filter the blood, generating approximately 150 1 of fluid each day; most of this is reabsorbed and a concentrated urine (approximately 1.5 1) is produced. The fact that urine volume can be varied independently of solute concentration is very important in terms of the regulation of osmolality of the blood and its total volume. However, a detailed discussion of renal function is outside the scope of this book.