Extracellular electrolytes

The concentrations and distribution of electrolytes are not fixed, because cell membranes are permeant to ions and to water. Movement of ions and water in and out of cells is determined by the balance of thermodynamic forces, which are normally close to equilibrium. Selective changes of ion concentrations cause movement of water in or out of cells to compensate for these alterations. The kidneys are a major site where changes in salt or water are sensed. The loss of fluids due to illness or disease may alter intracellular and extracellular electrolyte concentrations, with attendant changes in fluid movement in or out of cells. Changes of extracellular or intracellular ion concentrations, particularly for potassium, sodium, and calcium, can have profound effects on neuronal excitability and contractility of the heart and other muscles. 

Calcium is the principal extracellular electrolyte regulated by PTH, calcitonin, and D3. Extracellular calcium is a critical component of signal transduction across the plasma membrane, which regulates a wide spectrum of physiological events including muscle contraction, secretion of neurotransmitters and hormones, and the ac-... 

All living systems require the major cations and anions Na+, K+, Ca +, Mg +, CU, P04 and S04 . These ions are involved in the (1) regulation of intra-and extracellular electrolyte balance, (2) maintenance of bioelectric potentials and function of bioexcitable membranes, (3) control of pH, (4) stabilization of membrane structure and integrity, (5) mineralization of endo- and exoskeletons,... 

The model to the left in Figure 10.3 is often used to model skin impedance. For instance, R may represent the deeper viable parts and the parallel R and C components represent the poorly conducting stratum corneum (SC). The model to the right may be used for tissue as shown in Figure 10.2. Then G models the extracellular electrolyte, C, the cell membranes, and R the intracellular resistance. Fixed component values in the two models can be found so that they have exactly the same impedance spectrum. 

The intracellular and extracellular electrolytes are listed in Table 2.6. They cause an electrolytic conductivity on the order of 1 S/m. Up to at least 10 MHz, it is considered to be frequency independent (Cooper, 1946). 

Consider a cell model such as the one in Figure 5.6, with the cell interior completely insulated from the outside by a perfect membrane without channels. The intracellular and extracellular electrolytes are very conductive. The interior has been polarized by an initial transport of some cations out from the interior and into the extracellular volume. 

Cautious intravenous infusion of isotonic sodium chloride solution improves the patient s condition. Although sodium chloride solution is neutral, the provision of the principal extracellular electrolytes provides the necessary osmotically active material to return the extracellular fluid volume towards normal. This switches the drive from mechanisms for retention of electrolyte to those for correction of metabolic alkalosis. The body puts its own house in order so far as the acid-base problems are concerned and the situation is saved. 

Diuretic therapy is a common iatrogenic origin of metabolic disturbances of acid-base physiology. Diuretics are administered for their naturetic properties particularly in patients with cardiac, hepatic, pulmonary and renal disease, to rid the body of excess extracellular fluid. When the loss of sodium is matched by losses of other extracellular electrolytes in proportion to their extracellular concentrations, no disturbance of acid-base balance occurs. In cases where there is a disproportionate loss of bicarbonate, the result is metabolic acidosis. Conversely when there is an exaggeration of loss of ammonium or chloride ions by comparison with sodium, this leads to metabolic alkalosis. 

Clinical Applications Perhaps the area in which ion-selective electrodes receive the widest use is in clinical analysis, where their selectivity for the analyte in a complex matrix provides a significant advantage over many other analytical methods. The most common analytes are electrolytes, such as Na+, K+, Ca +, H+, and Ch, and dissolved gases, such as CO2. For extracellular fluids, such as blood and urine, the analysis can be made in vitro with conventional electrodes, provided that sufficient sample is available. Some clinical analyzers place a series of ion-selective electrodes in a flow... 

Sodium chloride [7647-14-5] is an essential dietary component. It is necessary for proper acid—base balance and for electrolyte transfer between the iatra-and extracellular spaces. The adult human requirement for NaCl probably ranges between 5—8 g/d. The normal diet provides something ia excess of 10 g/d NaCl, and adding salt duting cooking or at the table iacreases this iatake. 

The integrity of mammalian kidneys is vital to body homeostasis, because the kidneys play the principal role in the excretion of metabolic wastes and the regulation of extracellular fluid volume, electrolyte balance, and acid-base... 

A surgical implant is constantly bathed in extracellular tissue fluid. Basically water, this fluid contains electrolytes, complex compounds, oxygen and carbon dioxide. Electrolytes present in the largest amounts are sodium (Na ) and chloride (Cl ) ions. Most of the fluids existing in the body (such as blood, plasma and lymph) have a chloride content (and pH) somewhat similar to that of sea water (about 5 to 20g/l and pH about 8) . 

A 0-9% salt solution is considered to be isotonic with blood. Other electrolytes present include bicarbonate ions (HCOj ) and small amounts of potassium, calcium, magnesium, phosphate, sulphate and organic acid ions. Included among the complex compounds and present in smaller amounts are phospholipids, cholesterols, natural fats, proteins, glucose and amino acids. Under normal conditions the extracellular body fluid is slightly alkaline with a pH of 7-4. ... 

Filter aids are widely used in die fermentation industry to improve the efficiency of filtration. It is a pre-coated filter medium to prevent blockage or blinding of the filter by solids, which would otherwise wedge diemselves into the pores of the cloth. Filter aid can be added to the fermentation broth to increase the porosity of the cake as it formed. This is only recommended when fermentation product is extracellular. Filter aid adds to the cost of filtration. The minimum quantity needed to achieve the desired result must be established experimentally. Fermentation broths can be pretreated to improve filtration characteristics. Heating to denature proteins enhances the filterability of mycelial broths such as in penicillin production. Alternatively, electrolytes may be added to promote coagulation of colloids into larger, denser particles, which are easier to filter. The filtration process is affected by the viscosity and composition of the broth, and the cell cake.5... 

Plasma consists of water, electrolytes, metabolites, nutrients, proteins, and hormones. The water and electrolyte composition of plasma is practically the same as that of ail extracellular fluids. Laboratory determinations of levels of Na, K+, Ca, CL, HC03, PaC02, and of blood pH are important in the management of many patients. 

Identify the electrolytes primarily found in the extracellular and intracellular fluid compartments. 

The extracellular fluid (ECF) is the fluid outside the cell and is rich in sodium, chloride, and bicarbonate. O The ECF is approximately one-third of TBW (14 L in a 70-kg man or 12 Lin a 70-kg woman) and is subdivided into two compartments the interstitial fluid and the intravascular fluid. The interstitial fluid (also known as lymphatic fluid) represents the fluid occupying the spaces between cells, and is about 25% of TBW (10.5 L in a 70-kg man or 8.8 L in a 70-kg woman). The intravascular fluid (also known as plasma) represents the fluid within the blood vessels and is about 8% of TBW (3.4 L in a 70-kg man or 2.8 L in a 70-kg woman). The ECF is approximately one-third of TBW or 14 L in a 70-kg male. Because the exact percentages are cumbersome to recall, many clinicians accept that the ECF represents roughly 20% of body weight (regardless of gender) with 15% in the interstitial space and 5% in the intravascular space.6 Note that serum electrolytes are routinely measured from the ECF. 

Regulation of inorganic electrolyte concentration in extracellular fluid... 

The process of tubular reabsorption is essential for the conservation of plasma constituents important to the body, in particular electrolytes and nutrient molecules. This process is highly selective in that waste products and substances with no physiological value are not reabsorbed, but instead excreted in the urine. Furthermore, reabsorption of many substances, such as Na+, H+, and Ca++ ions, and water is physiologically controlled. Consequently, volume, osmolarity, composition, and pH of the extracellular fluid are precisely regulated. 

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