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| solutions containing free ions behaving as electrically conductive media. Because they consist of ions in solution, electrolytes are ionic solutions |
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| Electrolyte solutions are formed when |
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| a salt is placed into a solvent and the individual components dissociate |
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| Electrolytes are classified |
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| based on their migration in and electrical field. |
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| the cathode and are said to be positively charged. |
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| The principle cations in human plasma are |
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| the anode and are said to be negatively charged. |
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| The principle anions in human plasma are |
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| includes the water within and outside the cell and that normally found in the gastrointestinal and urogential systems |
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| Total body water is subdivided into two compartments: |
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| the intracellular fluid (ICF) and the extracellular fluid (ECF) |
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| is the medium for all metabolic exchange |
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| medium for cellular metabolic reactions |
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| Total body water varies inversely with |
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| the sole compartment of total body water |
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| Plasma volume percent of total body weight |
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| Total body water as a percentage of body weight decreases |
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| during intrauterine development and reaches the normal adult values by age three. |
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| The absolute volume of the water compartments |
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| all increase with growth. |
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| mixture of water and macromolucules, i.e., proteins, lipids. |
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| Plasma water refers strictly |
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| The concentration of ions in the plasma is |
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| lower than their actual concentration in the plasma water. |
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| The ions are present solely in the |
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| Reported concentrations represent |
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| the ion concentration in the plasma |
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| The actual concentration of the ions in the plasma water impact |
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| diffusion across the capillary membrane. |
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| Increased concentrations of macromolecules in the plasma will result in |
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| lower measured ion concentration even though plasma water ion concentrations and activity may be normal. |
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| requiring that the sum of all charged particles must be equal. |
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| the sum of the cations must |
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| equal the sum of the anions so no net electrical charge exists |
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| The sum of the measured cations (Na+ +K+) exceeds the sum of the measure anions (CL- + HCO3-). |
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| unmeasured anions are greater than the unmeasured cations. |
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| Increases in the anion gap usually indicates |
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| an increase in one or more of the unmeasured anions. Used in the differential diagnosis of metabolic acidosis |
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| Reference range Anion Gap |
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| Major Clinical Uses of the Anion Gap |
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To signal the presence of a metabolic acidosis
Help differentiate between causes of a metabolic acidosis: high anion gap versus normal anion gap metabolic acidosis. |
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| In an inorganic metabolic acidosis |
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| the infused Cl- replaces HCO3 and the anion gap remains normal. |
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| the lost bicarbonate is replaced by the acid anion which is not normally measured. This means that the AG is increased |
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| Major functions of blood electrolytes |
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Maintenance of osmotic pressure
Water distribution
Maintenance of pH
Regulation of the proper function of the heart and muscles
Oxidation-reduction reaction – electron transfer
Catalytic reactions by serving as cofactors for enzymes |
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| Theoretical Osmotic Pressure |
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| O.P. (t) (mmHg) = 19.3 mmHg/mOsm/L X Osmolality (mOsm/L) |
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| Theoretical osmotic pressure is proportional |
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| the force that tends to move water from dilute solutions to concentrated solutions |
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| effective osmotic pressure |
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| When a membrane is permeable to a solute the solute exerts no osmotic pressure across the membrane |
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| The effective osmotic pressure is dependent upon |
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| the total number of solute particles in solution and the permeability of the membrane to the solute |
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| The higher the permeability of the membrane to the solute |
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| the lower is the effective osmotic pressure of a solution of that solute at any given osmolality. |
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| Measurements of osmolality measure the |
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| theoretical not the effective osmotic pressure |
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| A solution with an effective osmotic pressure greater than plasma |
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| A solution with a theoretical osmotic pressure greater than plasma |
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| refer to solutions with effective and theoretical osmotic pressures less than plasma. |
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| colloid osmotic pressure. |
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| The effective osmotic pressure of plasma and the interstitial fluid across the capillary membrane |
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| Capillary endothelium are impermeable to |
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| larger protein molecules (colloids). |
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| These colloids are responsible for |
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| the effective osmotic pressure between the plasma and the interstitial fluid |
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| Water distribution across the capillary endothelial membrane are controlled by |
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| the balance between filtration and reabsorption forces |
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| The principle filtration force in the plasma is |
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| hydrostatic pressure the primary reabsorption force is the colloid osmotic pressure. |
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| Plasma hydrostatic pressure drive water |
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| colloid osmotic pressure draws water |
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| is the pressure that the fluid exerts on the walls of its container. In human body, the hydrostatic pressure refers to the pressure that the blood exerts on the walls of the arteries and veins. |
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| is the pressure required to prevent the flow of water across a semi permeable membrane via osmosis. |
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| Water and solute distribution across the cell membrane depend on |
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| on the integrity of the cell membrane and on osmotic and electrochemical forces |
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| The permeability of the cell membrane to a solute is directly related to |
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| the lipid solubility of the solute and inversely related to hydrophilicity and molecule size |
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| Extracellular osmolality is maintained between |
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| 285 and 300 mOsm/L through the balance between water intake an excretion. |
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| Ingestion, Water in foodstuffs and Oxidative metabolism |
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| Urine, Insensible Perspiration and GI water loss (stool) |
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| Kidney is principally responsible for |
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| regulating the volume and composition of the body fluids |
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| Occurs through the skin and the respiratory tract |
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| Insensible Water Loss varies directly with |
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| ambient temperature, body temperature and activity |
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| Insensible Water Loss varies inversely with |
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| Defined as decrease in total body water with a relatively normal total body sodium |
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| simple dehydration results from |
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| failure to replace obligatory water losses, regulatory failures |
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| simple dehydration associated with |
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| hypernatremia and hyperosmolarity because water balance is negative and sodium balance is normal |
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| ^ECF osmolality as water is lost results in |
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| movement of water out of the ICF. Results in a contraction of both the ECF and the ICF. |
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| Dehydration due to Water and Sodium Loss |
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| Most often dehydration involves a net negative balance in both water and sodium |
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| Hypernatremic (hyperosmolar) dehydration |
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| water balance is more negative than sodium, most common |
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| Normonatremic (isoosmolar) dehydration |
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| water and sodium balance are equally negative |
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| Hyponatremic (hypoosmolar) dehydration |
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| water balance is less negative than sodium balance |
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| Hypernatremic (hyperosmolar) dehydration Changes to Extracellular Volume |
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| ECF volumes effected the least. ^ECF Osm. Draws water from the ICF – ICF contracts |
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| Normonatremic (isoosmolar) dehydration Changes to Extracellular Volume |
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| no change to ECF Osm – no net water flow |
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Hyponatremic (hypoosmolar) dehydration
Changes to Extracellular Volume |
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| Greatest effect to ECF volume – vOsm. Of ECF causes water to move into the cells – ICF volume expanded |
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| Defined as increased total body water |
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| Water intoxication usually results from |
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| impaired renal excretion resulting from excessive ADH secretion |
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| Water intoxication usually results in |
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| hyponatremia and hypoosmolality producing a expansion of the ECF and ICF |
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| If Na is normal the ^ in total body water |
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| water is confined to the EC |
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| If Na is vthan the increase in water is |
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| shared between the ECF and ICF. |
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| difference in Na concentration between the ECF and the ISF |
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| Sodium balance is a result of |
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| carefully controlled intake and output mechanisms |
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| occurs through three primary routes: GI tract, skin, and urine |
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| Sodium concentration in sweat is decreased by |
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| Sodium concentration in sweat is increased by |
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| Sodium Loss through the skin can be extensive in |
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| severe burns and exudative skin lesions |
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| The principle route for sodium excretion |
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| Renal excretion regulated through |
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| Management of Na+ reabsorption in the distal tubule |
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| establishes the renal threshold for Na+ – 110mM/L which determine the amount of Na+ excreted in the urine. |
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| Occurs when the output of sodium exceeds intake |
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| Indicates a decreased plasma sodium concentration |
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| Sodium deficit greater than water deficit, Fluid Shift – ECF to ICF, Psuedohyponatremia, Water excess greater than sodium excess |
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| Occurs when sodium intake exceeds sodium output usually because of a defect in the homeostatic mechanism |
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| Hypernatremia- conditions |
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| Cardiac Failure, Liver Disease, Renal Disease (nephrotic syndrome), Hyperaldosteronism, Pregnancy, CHF |
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| Sodium excess greater than water excess, Water deficits greater than sodium deficits, Hyperventilation, Diabetes insipidus, Osmotic diuresis, Diminished fluid input – diminished thirst, Essential hypernatremia, Certain diarrheal states and vomiting |
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| Specimen for sodium determinations |
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| serum, plasma whole blood sweat, urine, feces, GI fluids |
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| Factors that increase cellular influx of K+ |
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| Insulin, aldosterone, alkalosis, ? adrenergic stimulation |
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| Factors that decrease cellular influx of K+ |
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| Acidosis, alpha adrenergic stimulation, tissue hypoxia |
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| Factors regulating distal tubular secretion of K+ include |
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Intake of Na+ and K+
Water flow rate in the distal tubules
Plasma levels of mineralocorticoids
Acid-base status |
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| Increased K+ levels produce |
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| symptoms of mental confusion, weakness, numbness and tingling in the extremities, slowed heart rate, peripheral vascular collapse and cardiac arrest. |
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| + levels greater than 7.5 mM/L, <10.0 is fatal |
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| Increased potassium intake |
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| Diet, Oral supplementation, IV administration, High dose potassium penicillin use, transfusion |
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| Decreased potassium excretion |
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| Renal Failure, Adrenal failure (hypoaldosteronism), diuretics that block distal K+ secretion (spironolactone), Primary defects in renal tubular handling of K+ secretion. |
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| Decreased potassium intake, Increased GI Loss, Increased urinary loss |
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| Occurs with an increased plasma K+ concentration |
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| Occurs with decrease plasma K+ concentrations |
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| Pseudohyperkalemia, Intracellular to extracellular shifts, High potassium intake, and Decreased potassium excretion |
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| Extracellular to intracellular K+ Shift, Decreased potassium intake, Increased GI Loss, and Increased urinary loss |
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| Specimens for the determination of K+ |
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| serum or plasma must avoid hemolysis. |
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| Major anion of the extracellular fluid |
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Output of Cl-GI tract, skin, urine
occurs through three principle routes: |
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| Accumulation occurs when intake exceeds output because of some abnormality n homeostatic mechanism |
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| Occurs when output exceeds intake |
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