advanced physiology fluid and electrolytes part 2

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ADVANCED PHYSIOLOGY FLUID & ELECTROLYTES PART 2 Instructor Terry Wiseth NORTHLAND COLLEGE

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ELECTROLYTE BALANCEThe exchange of interstitial and intracellular fluid is controlled mainly by the presence of the electrolytes sodium and potassiumNa+K+Na+K+Na+K+Na+K+

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ELECTROLYTE BALANCEPotassium is the chief intracellular cation and sodium the chief extracellular cation Because the osmotic pressure of the interstitial space and the ICF are generally equal, water typically does not enter or leave the cellK+Na+

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ELECTROLYTE BALANCEA change in the concentration of either electrolyte will cause water to move into or out of the cell via osmosis A drop in potassium will cause fluid to leave the cell whilst a drop in sodium will cause fluid to enter the cellK+H2OH2OH2OH2OH2OH2OH2OH2OK+K+K+Na+Na+Na+Na+Click to see animation

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ELECTROLYTE BALANCEA change in the concentration of either electrolyte will cause water to move into or out of the cell via osmosis A drop in potassium will cause fluid to leave the cell whilst a drop in sodium will cause fluid to enter the cellK+H2OH2OH2OH2OH2OH2OH2OH2OK+K+K+Na+Na+Na+Na+Click to see animation

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ELECTROLYTE BALANCEAldosterone, ANP and ADH regulate sodium levels within the body, while aldosterone can be said to regulate potassiumK+Na+aldosteroneADHANP

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ELECTROLYTE BALANCESodium (Na+) ions are the important cations in extracellular fluid Anions which accompany sodium are chloride (Cl-) and bicarbonate (HCO3-) Considered an indicator of total solute concentration of plasma osmolalityNa+HCO3-Cl-

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ELECTROLYTE BALANCESodium ions are osmotically important in determining water movements A discussion of sodium must also include Chlorine Bicarbonate Hydrogen ions Potassium and calcium serum concentrations are also important electrolytes in the living systemH2OH2OH2OH2OH2OH2OH2OH2OH2OH2OH2OH2OH2OH2OH2O

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ELECTROLYTE BALANCESClickHypercalcemia - elevated calcium levels Hypokalcemia -- lowered calcium levelsClickHyperkalemia -- elevated potassium levels Hypokalemia ---- lowered potassium levelsHypernatremia - elevated sodium levels Hyponatremia -- lowered sodium levels

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HYPERNATREMIANormal range for blood levels of sodium is app. 137 - 143 meq/liter Hypernatremia refers to an elevated serum sodium level (145 -150 meq/liter) Increased levels of sodium ions are the result of diffusion and osmosisNa+

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SODIUM PRINCIPLES1) Sodium ions do not cross cell membranes as quickly as water doesNa+H2OH2OH2OH2OH2ONa+

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SODIUM PRINCIPLES2) Cells pump sodium ions out of the cell by using sodium-potassium pumpsNa+Na+Na+Na+

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SODIUM PRINCIPLES3) Increases in extracellular sodium ion levels do not change intracellular sodium ion concentrationNa+Na+Na+Na+Na+Na+Na+Na+Na+Na+Na+Na+Na+Na+Na+Na+Na+Na+Na+Na+

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RESULTS OF HYPERNATREMIA1) Water is osmotically drawn out of the cells Resulting in dehydration 2) Increase in extracellular fluid volumeExtracellular fluid volumeIntracellular fluid volume

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CNS REACTION TO HYPERNATREMIAIn the CNS tight junctions exist between endothelial cells of the capillary walls These junctions restrict diffusion from capillaries to the interstitium of the brain blood-brain barrier Increased levels of sodium ions in the blood does not result in increased sodium ions in brain interstitial fluid

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CNS REACTION TO HYPERNATREMIAAs the result of an osmotic gradient, water shifts from the interstitium and cells of the brain and enters the capillaries The brain tends to shrink and the capillaries dilate and possibly rupture Result is cerebral hemorrhage, blood clots, and neurological dysfunctionH2O

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CNS PROTECTIVE MECHANISMThere is an unknown mechanism that protects the brain from shrinkage Within about 1 day Intracellular osmolality of brain cells increases in response to extracellular hyperosmolality

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CNS PROTECTIVE MECHANISMIdiogenic osmoles accumulate inside brain cells K+, Mg+ from cellular binding sites and amino acids from protein catabolism These idiogenic osmoles create an osmotic force that draws water back into the brain and protects cells from dehydrationH2O

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CAUSES OF HYPERNATREMIA1) Water loss 2) Sodium ion overload Most cases are due to water deficit due to loss or inadequate intake Infants without access to water or increased insensible water loss can be very susceptible to hypernatremia

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WATER LOSSDiabetes insipidus caused by inadequate ADH or renal insensitivity to ADH results in large urinary fluid loss Increased fluid loss also occurs as the result of osmotic diuresis (high solute loads are delivered to the kidney for elimination)

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WATER LOSSDiabetes mellitus results in loss of fluids as well by creating an osmotic pull (increased urine solute concentration) on water into the tubules of the kidneyGlucoseGlucoseGlucoseGlucoseGlucoseGlucoseGlucoseGlucoseGlucoseGlucoseGlucoseH2OH2OH2OH2OH2OH2OH2OH2OH2OH2OH2OH2OClick to animate

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WATER LOSSHigh protein feedings by a stomach tube create high levels of urea in the glomerular filtrate producing an osmotic gradient the same as glucose does and increased urinary output results

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SODIUM EXCESSOccurs less frequently than water loss Retention or intake of excess sodium ex: IV infusion of hypertonic sodium ion solutions Aldosterone promotes sodium and water retention by the kidney High levels of aldosterone may result in mild hypernatremia

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CAUSES OF HYPERNATREMIA

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TREATMENT OF HYPERNATREMIARe-hydration is the primary objective in most cases Decreases sodium concentrations A point of concern is when and how rapid the re-hydration occurs

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TREATMENT OF HYPERNATREMIAAfter 24 hours the brain has responded by producing idiogenic osmoles to re-hydrate brain cells If this adaptation has occurred and treatment involves a rapid infusion of dextrose for example There is danger of cerebral edema with fluid being drawn into brain tissues

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Last Updated: 8th March 2018

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