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. These pumps transport ions against their concentration gradients to maintain the cytosol fluid composition of the ions.Clinical assessment of acid-base disorders depends on measurements made in the blood, part of the extracellular compartment.
The reason for these specific sodium and potassium ion concentrations are Na+/K ATPase pumps that facilitate the active transport of these ions. In contrast to extracellular fluid, cytosol has a high concentration of potassium ions and a low concentration of sodium ions. The cytosol also contains much higher amounts of charged macromolecules, such as proteins and nucleic acids, than the outside of the cell. The concentrations of the other ions in cytosol or intracellular fluid are quite different from those in extracellular fluid. The cell membrane separates cytosol from extracellular fluid, but can pass through the membrane via specialized channels and pumps during passive and active transport. The pH of the intracellular fluid is 7.4. Most of the cytosol is water, which makes up about 70% of the total volume of a typical cell. These enzymes are involved in the biochemical processes that sustain cells and activate or deactivate toxins. This mixture of small molecules is extraordinarily complex, as the variety of enzymes that are involved in cellular metabolism is immense. The cytosol or intracellular fluid consists mostly of water, dissolved ions, small molecules, and large, water-soluble molecules (such as proteins). The composition of tissue fluid depends upon the exchanges between the cells in the biological tissue and the blood.