For example, central nervous system interstitial fluid (ISF) may acidify as a result of an intracranial hemorrhage. Other transcellular fluids, or spaces, include the cerebrospinal fluid, and pleural and peritoneal spaces, but because these are not open to the outside environment, they more often reflect ECF acid-base status rather than determine it.Ĭlinical practice provides many examples in which treatment of an acid-base disturbance of the ECF may have damaging, unobserved effects within the ICF. These particular spaces are open to the external environment, and, as such, their contents, to variable extents, are lost from the body in health and disease. Examples are the gastrointestinal tract, the renal tubular lumen (urinary space), and sweat gland ducts. A transcellular space is part of the ECF lined by epithelial cells. The ECF is further compartmentalized to the intravascular plasma volume, the interstitial fluid (ISF), and the transcellular fluids. The ECF usually accounts for one-third of total body water compared with the two-thirds of body water that constitutes the ICF ( 54, 65). Advances in methods to measure in vivo cell pH ( 25, 41, 78), as well as pH in various organs under various conditions, will greatly improve our understanding and management of human acid-base disorders. Although much is known concerning mechanisms of its regulation ( 8, 11), ICF acid-base balance is technically more difficult to assess, is heterogeneous within subcellular compartments, and, since various organs regulate pH with differing degrees of precision, the measure of a single set of blood values cannot accurately reflect the health of all organs. Maintenance of intracellular fluid (ICF) pH is critical to processes such as protein synthesis, intermediate metabolism, cell growth, and reproduction. Have we been looking in the wrong-but easier-place to assess clinical acid-base disturbances? Although recent studies suggest important roles of extracellular fluid (ECF) pH and lactate in activation of T cells in immune function, formation of the extracellular matrix, and angiogenesis ( 28, 34), it is primarily the simplicity of measuring accessible blood that gives it such prominence as a surrogate to determine the health of tissues. The passerby asks why isn’t he looking down the street, and the man answers, “The light is better under the street lamp.” A passerby, offering to assist him, asks the man where he dropped his keys. Īcid-Base Balance Within Body Fluid CompartmentsĪ well-known joke involves a man looking for his lost keys under a street lamp.
Electroneutrality of electrolytes in the ECF is discussed in the context of reciprocal changes in Cl − or non Cl − anions and H C O 3 −. The role of secretory gastrointestinal epithelia and renal epithelia with respect to normal pH homeostasis and clinical disorders are considered. This review suggests a process of internal and external balance for pH regulation, similar to that of potassium.
The generation of acid-base disorders and the associated disruption of electrolyte balance are considered in the context of these membrane transporters. This review considers the determinants of the extracellular fluid pH related to the ion transport processes at the interface of cells and the interstitial fluid, and between epithelial cells lining the transcellular contents of the gastrointestinal and urinary tracts that open to the external environment. Intracellular and interstitial compartment acid-base balance is complex and heterogeneous. Yet much of the metabolic importance of these disorders concerns intracellular events.
Clinical assessment of acid-base disorders depends on measurements made in the blood, part of the extracellular compartment.