Interstitial fluid composition

Haar HP, List H, Meacham GBK (2006) Direct monitoring of interstitial fluid composition. 

Factors known to influence the clearance of drugs from interstitial sites, following extravasation or parenteral interstitial or transepithelial administration, include size and surface characteristics of particles, formulation medium, the composition and pH of the interstitial fluid, and disease within the interstitium. Studies indicate that soluble macromolecules smaller than 30 nm can enter the lymphatic system, whereas particulate materials larger than 50 nm are retained in the interstitial sites and serve as a sustained-release depot. The use of lipids or an oil in a formulation and the presence of a negative surface charge all appear to... 

Embedded within the brain are four ventricles or chambers that form a continuous fluid-filled system. In the roof of each of these ventricles is a network of capillaries referred to as the choroid plexus. It is from the choroid plexuses of the two lateral ventricles (one in each cerebral hemisphere) that cerebrospinal fluid (CSF) is primarily derived. Due to the presence of the blood-brain barrier, the selective transport processes of the choroid plexus determine the composition of the CSF. Therefore, the composition of the CSF is markedly different from the composition of the plasma. However, the CSF is in equilibrium with the interstitial fluid of the brain and contributes to the maintenance of a consistent chemical environment for neurons, which serves to optimize their function. 

The lymphatic capillaries are close-ended vessels in close proximity to blood capillaries and, like blood capillaries, lymphatic capillaries are composed of a single layer of endothelial cells. However, large gaps in between these cells allow not only fluid, but also proteins and particulate matter to enter the lymphatic capillaries quite readily. Once the fluid has entered these capillaries, it is referred to as lymph. Not surprisingly, the composition of this fluid is similar to that of the interstitial fluid. 

Body fluids are partitioned between the intracellular fluids (ICF), which constitute two-thirds of total body water, and extracellular fluids (ECF), which constitute one-third of total body water. The ECF consists of plasma and interstitial fluid plus lymph. The ionic composition differs substantially between ECF and ICF (Table 21.1). Sodium is the primary cation in ECF, whereas potassium is the principal intracellular cation. 

Fogh-Andersen N, Altura BM, Altura BT, Siggaard-Andersen O. Composition of interstitial fluid. Clinical Chemistry 1995, 41, 1522-1525. 

Cells in the higher organism are bathed in interstitial fluid to which waste products are added and from which substances are removed by processes of diffusion. Regulation of the composition of interstitial fluid is achieved by diffusion through the capillary walls to and from the circulating blood. Through these mechanisms, cells are able to maintain their cellular environment within certain limits and are protected temporarily from large external physical and chemical variations. 

Interstitial fluids bathe the cells and tissues. With respect to the electrolytes and other constituents, physiology textbooks indicate that the interstitial fluids are generally similar in composition to the plasma, with the important... 

Intracellular fluids (also called the cytosol) are quite different compositionally from plasma and interstitial fluids (Table 4, Figures 4 and 5). The internal pH of many cells is maintained near 6.9-7.0. via various membrane transport mechanisms such as Na" /H and CP/HCO exchangers, and various phosphate and protein buffers. In contrast to the plasma, the intracellular fluids have substantially lower concentrations of sodium, calcium, chloride, and bicarbonate and higher to substantially higher concentrations of potassium, magnesium,... 

A variety of literature sources that discuss simulated lung fluids (SLFs) imply that the aqueous component of lung fluid is an electrolyte fluid generally similar in composition to that of interstitial fluid with pH near 7.4 (Table 4). Redox conditions in the lung fluids are not readily available from the literature. It is unclear which organic redox couples are active in the pulmonary fluids, and how these may drive redox equilibria to lower Eh values than those in equilibrium with the 0.132 atm PO2 present in the alveoli. 

Figure 9 Plots showing the calculated mineral saturation indices as a function of pH for hydroxylapatite, quartz, and various asbestos-forming minerals in electrolyte solutions approximating the electrol)he compositions of lung fluids (approximated by interstitial fluids, upper plot) and intracellular fluids (lower plot). Electrolyte concentrations used as input were taken from Table 4. The CO2 partial pressure was fixed at the value for venous plasma for each speciation at a different pH. Organic species such as amino acids and other organic acids were not included in the calculations, but likely would have the effect of decreasing the calculated saturation indices somewhat due to their...

Ambient temperature affects the composition of body fluids. Acute exposure to heat causes the plasma volume to expand by an influx of interstitial fluid into the intravascular space, and by reduction of glomerular filtration. The. plasma protein concentration may decrease by up to 10%. Sweating may cause salt and water loss, but usually there are no changes in the plasma sodium and chloride concentrations. Plasma potassium concentration may decrease by as much as 10% as potassium is taken up by the cells. If sweating is extensive, hemoconcentration rather than hemodilution may occur. 

Basal cells that stop dividing also stop secreting a basal lamina and lose their attachment. They are squeezed by adjacent, dividing basal cells into the body of the junctional epithelium and are expelled into the base of a sulcus. The few tight junctions in the body of the junctional epithelium are consistent with its permeability to interstitial fluid. The rapidly dividing cells of both internal and external basal layers express K5 and K14 like all stratified epithelial basal cells, but the interior cells express K4 and K13, not K1 and K10 (Fig. 5.11). The composition of the internal basal lamina is described in Fig. 5.7b. 

Table 13.1 Interstitial and gingival crevicular fluid composition ...

Physiological fluids within the human body can be divided into human intracellular fluid (hICF, with a volume of 271 for a 70 kg person) and human extracellular fluid (hECF, 131). Extracellular fluid can further be subdivided into two sub-compartments, that is human interstitial fluid (hISF, 9.51) and the liquid component of blood (plasma, 3.51 for a 70 kg person) (Tas, 2014). While the extracellular fluid represents the fluid outside cells, and intracellular fluid the fluid within cells, the interstitial fluid is the tissue fluid found between cells. There is a striking difference between the compositions of extracellular and intracellular fluids as presented in Table 7.7. Since the composition of blood plasma is close to that of hECF (Krebs, 1950), synthetic SBFs developed by various research groups frequently attempt to emulate these compositions (Table 7.8). 

Further refinements to this model of the froth formation process can be made by substituting a representative middlings composition for the interstitial fluid. In addition, the assay of bitumen films surrounding the air bubbles can be modified to account for the presence of hydrophobic solids and emulsified water. 

In the capillary beds of most organs, a rapid passage of molecules occurs from the blood through the endothelial wall of the capillaries into the interstitial fluid. Thus, the composition of interstitial fluid resembles that of blood, and specific receptors or transporters in the plasma membrane of the cells being bathed by the interstitial fluid may directly interact with amino acids, hormones, or other compounds from the blood. In the brain, transcapillary movement of substrates in the peripheral circulation into the brain is highly restricted by the blood-brain barrier. This barrier hmits the accessibility of blood-borne toxins and other potentially harmful compounds to the neurons of the CNS. 

The clay mineral associations may be used as indicators of temperature and degree of metamorphism reached by their enclosing rocks (Kubler 1964,1973). The chemical composition of the rock and of the interstitial fluid together with the mineralogy of the terrigenous rocks also furnishes characteristic indicators for the determination of the mineral associations formed at these temperatures. 

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