1 / 21

Chapter 16: Electrolytes

Chapter 16: Electrolytes. By George A. Harwell. Introduction to Electrolytes. Electrolytes: ions capable of carrying an electric charge Two types 1. Anions have negative charge & move toward anode. 2. Cations have positive charge & move toward cathode.

genica
Download Presentation

Chapter 16: Electrolytes

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Chapter 16: Electrolytes By George A. Harwell

  2. Introduction to Electrolytes • Electrolytes: ions capable of carrying an electric charge • Two types • 1.Anions have negative charge & move toward anode. • 2.Cations have positive charge & move toward cathode. • Electrolytes are an essential component in many processes: • Volume & osmotic regulation (Na, Cl, K) • Myocardial rhythm & contractility (K, Mg, Ca) • Cofactors in enzyme activation (Mg, Ca, Zn) • Blood coagulation (Ca, Mg)

  3. Water • Water = 40–75% of human body weight • Declines with age & obesity • Less in women than in men, due to higher % of body fat • Water is solvent for all processes in human body: • Transports nutrients to cells • Determines cell volume by its transport into & out of cells • Removes waste products by way of urine • Acts as body’s coolant by way of sweating • Found in intra- (2/3) & extracellular (1/3) compartments

  4. Water (cont’d) • Osmolality • A physical property of a solution based on concentration of solutes (millimoles) per kilogram of solvent (w/w) • Related to changes in properties of solution relative to pure water (decreases in freezing point & vapor pressure) • Clinical significance of osmolality • Osmolality is parameter to which hypothalamus responds. • Regulation of osmolality affects plasma sodium concentration. • Regulation of sodium & water controls blood volume. • Determination of osmolality: may be measured in serum or urine

  5. Water (cont’d) • Responses to changes in blood osmolality and blood volume

  6. The Electrolytes • Sodium • Most abundant cation in ECF (90%) & largely determines osmolality of plasma • Sodium concentration in ECF is much larger than inside cells. • Active transport systems, such as ATPase ion pumps, prevent sodium equilibrium in all cells. • Regulation • Intake of water in response to thirst • Excretion of water • Blood volume status

  7. The Electrolytes (cont’d) • Sodium • Clinical applications • Hyponatremia: lower-than-normal (<135 mmol/L) concentration of sodium in serum • Hypernatremia: higher-than-normal concentration of sodium in serum • Determination of sodium • Specimen: serum, plasma, whole blood, urine, sweat • Methods: Ion-selective electrodes method is most common.

  8. The Electrolytes (cont’d) • Potassium • The major intracellular cation in body; concentration 20 times greater inside cells than outside • Functions include: • Regulation of neuromuscular excitability • Contraction of heart • ICF volume • Hydrogen ion concentration • Because K+ is intracellular, it is critical for the laboratorian to be aware of a hemolysis in a serum/plasma sample, as this can falsely elevate the K+ results.

  9. The Electrolytes (cont’d) • Potassium • Regulation • Kidneys regulate potassium balance. • Potassium uptake from EFG into cells normalizes acute rise in plasma potassium concentration due to increased intake. • Factors that influence distribution of potassium: • 1. Inhibition of NaK ATPase pump by certain conditions • 2. Insulin promotes potassium ions entering muscle & liver. • 3. Catecholamines promote cellular entry of potassium.

  10. The Electrolytes (cont’d) • Potassium • Regulation • Exercise increases plasma potassium. • Hyperosmolality depletes potassium. • Cellular breakdown releases potassium into ECF. • Clinical applications • Hypokalemia: lower-than-normal plasma potassium • Hyperkalemia: higher-than-normal plasma potassium • Collection of samples: Proper collection & handling is important. • Determination of potassium: specimen: serum, plasma, urine

  11. The Electrolytes (cont’d) • Chloride • The major extracellular anion • Functions: maintains osmolality, blood volume, electric neutrality • Ingested in diet & almost completely absorbed by intestinal tract • Clinical applications • Hyperchloremia • Hypochloremia • Determinations of chloride • Specimen: serum, plasma, urine, sweat; method: ISE

  12. The Electrolytes (cont’d) • Bicarbonate • Second most abundant anion in ECF • Major component of buffering system in blood • Regulation • Reabsorbed by proximal (85%) & distal (15%) tubules in kidneys • Clinical applications • Metabolic acidosis may decrease bicarbonate. • Determinations of carbon dioxide • Specimen: serum, plasma; methods: ISE & enzymatic

  13. The Electrolytes (cont’d) • Magnesium • Physiology • 4th most abundant cation in body, 2nd intracellularly • Average human body contains 1 mole (24 g) of magnesium. • Widespread role in body • Glycolysis • Transcellular ion transport • Neuromuscular transmission • Synthesis of carbohydrates, proteins, lipids, nucleic acids • Release of & response to certain hormones

  14. The Electrolytes (cont’d) • Magnesium • Regulation • Rich sources of magnesium: raw nuts, dry cereal, hard drinking water, vegetables, meats, fish, & fruit • Consumption of processed foods can lead to inadequate intake. • Regulation of body magnesium controlled largely by kidneys, which can reabsorb it in deficiency states or excrete excess • Clinical applications: hypomagnesemia & hypermagnesemia • Specimen: nonhemolyzed serum or lithium heparin plasma • Methods: calmagite, formazan dye, methylthymol blue

  15. The Electrolytes (cont’d) • Calcium • Physiology • Essential for myocardial contraction • Blood-ionized calcium is closely regulated & has mean concentration in humans of about 1.18 mmol/L. • Important to maintain normal ionized levels during surgery & in critically ill patients • Regulation • Three hormones regulate calcium: PTH, vitamin D, calcitonin.

  16. The Electrolytes (cont’d) • Calcium • Distribution • 99% of body calcium is in bone; 1% is in blood & other ECF. • Of total amount in blood, 45% circulates as free calcium ions, 40% is bound to protein, & 15% is bound to anions. • Clinical applications • Hypocalcemia: calcium depletion • Hypercalcemia: elevated calcium levels • Determination of calcium • Specimen: serum, plasma; methods: dye binding

  17. The Electrolytes (cont’d) • Phosphate • Physiology • Found everywhere in living cells; participates in key biochemical processes • Regulation • May be absorbed in intestine from dietary sources, released from cells into blood, & lost from bone • Distribution: 80% in bone, 20% soft tissues, <1% serum/plasma • Clinical applications: hypophosphatemia & hyperphosphatemia • Specimen: serum, lithium heparin plasma; methods: formation of an ammonium phosphomolybdate complex

  18. The Electrolytes (cont’d) • Lactate • Biochemistry and physiology • Byproduct of an emergency mechanism that produces a small amount of ATP when oxygen is severely diminished • Regulation • Not specifically regulated; levels rise rapidly when oxygen delivery decreases below a critical level • Clinical applications: metabolic monitoring in critically ill patients • Specimen handling: Avoid using tourniquet. • Methods: Most common today are enzymatic methods.

  19. Anion Gap • Anion gap (AG): the difference between unmeasured anions & unmeasured cations • Created by concentration difference between commonly measured cations (Na+K) & anions (Cl+HCO3) • Useful for: • Indicating an increase in 1 or more unmeasured anions in serum • Quality control for analyzer used to measure electrolytes • Causes of elevation: uremia/renal failure, ketoacidosis, glycol poisoning, lactic acidosis, hypernatremia, error

  20. Anion Gap (cont’d) • Demonstration of anion gap from concentrations of anions and cations in normal state and in lactate acidosis

  21. Electrolytes and Renal Function • Summary of electrolyte excretion & conservation • Glomerulus: filters out large proteins & protein-bound particles • Renal tubules • Phosphate: reabsorption inhibited by PTH • Calcium: reabsorbed under influence of PTH • Magnesium: reabsorption occurs in Henle’s loop • Sodium: reabsorbed through 3 mechanisms • Chloride: reabsorbed by passive transport in proximal tubule • Potassium: reabsorbed by 2 mechanisms • Bicarbonate: recovered from glomerular filtrate

More Related