1. Part 1 Electrolytes

2. Electrolytes Electrolytes are ions capable of carrying an electricl charge Anions: (-) → Anode Cations: (+) → Cathode Major cations of the body Na +, K +, Ca +2 & Mg +2 Major anions of the body Cl -, HCO 3 -, HPO 4 -2 & SO 4 -2 M. Zaharna Clin. Chem. 2009 2

3. Essential Component in Numerous processes 1. Volume and osmotic pressure (Na +, K +, Cl - ) 2. Myocardial rhythm and contraction (K +, Mg 2+, Ca 2+ ) 3. Cofactors in enzyme activation (Mg 2+, Ca 2+, Zn 2+ ). 4. Regulation of ATPase ion pump (Mg 2+ ) 5. Acid/Base balance (pH) (HCO 3 -, K +, Cl - ) 6. Coagulation (Mg 2+, Ca 2+ ) 7. Neuromuscular (K +, Mg 2+, Ca 2+ ) The body has complex systems for monitoring and maintaining electrolyte concentrations M. Zaharna Clin. Chem. 2009 3

4. Maintenance of water homeostasis is vital to life for all organisms Maintenance of water distribution in various body fluids is a function of electrolytes (Na +, K +, Cl - & HCO 3 - ) M. Zaharna Clin. Chem. 2009 4

5. Water Average water content of human body is 40- 75% of total body weight. Solvent for all body processes Transport nutrients to cells Regulates cell volume Removes waste products → urine Body Coolant → sweating Water is located in intracellular and extracellular compartments M. Zaharna Clin. Chem. 2009 5

6. Water Normal plasma ~ 93 % H 2 O, the rest is mixture of Lipids and proteins. Concentration of ions within the cells and plasma is maintained by: 1. Energy consumption: Active transport 2. Diffusion: Passive transport Maintaining conc. of electrolytes affect distribution of water in compartments Most membranes freely permeable to water Conc. of ions on one side affect flow of water across the membrane M. Zaharna Clin. Chem. 2009 6

7. Osmolality Physical property of a solution based on the concentration of solutes per kilograms of solvent. (mOsm/Kg) Sensation of thirst & arginine vasopressin hormone (AVP) [formerly, Antidiuretic hormone (ADH)] are stimulated by hypothalamus in response to increased blood osmolality Thirst → more water intake AVP → increase water absorption in kidney M. Zaharna Clin. Chem. 2009 7

8. Clinical Significance Osmolality is the parameter to which hypothalmus responds to maintain fluid intake. The regulation of osmolality also affects the Na + concentration in plasma 90% of osmotic activity in plasma Another process affects Na + concentration is regulation of blood volume. M. Zaharna Clin. Chem. 2009 8

9. Clinical significance To maintain normal plasma osmolality (275-295 mOsm/Kg) hypothalamus must respond quickly to small changes 1-2% increase in osmolality: 4 fold increase in AVP secretion. 1-2% decrease in osmolality: shuts off AVP secretion. Renal water regulation by AVP and thirst play important roles in regulating plasma osmolality. Renal water excretion is more important in controlling water excess, whereas thirst is more important in preventing water deficit or dehydration. Consider what happens in several conditions. M. Zaharna Clin. Chem. 2009 9

10. Water Load Excess intake of water lower plasma osmolality Kidney is important in controlling water excess AVP and thirst are suppressed Water is not reabsorbed, causing a large volume of dilute urine to be excreted Hypoosmolality and hyponatremia usually occur in patients with impaired renal excretion of water M. Zaharna Clin. Chem. 2009 10

11. Water deficit As a deficit of water, plasma osmolality begins to increase Both AVP secretion and thirst are activated. Although AVP contributes by minimizing renal water loss, thirst is the major defense against hyperosmolality and hypernatremia. A concern in infants, unconscious patients, or anyone who is unable to either drink or ask for water M. Zaharna Clin. Chem. 2009 11

12. Regulation of blood volume Blood volume essential in maintaining blood pressure and ensure perfusion to all tissue and organs. Regulation of both sodium & water are interrelated in controlling blood volume Renin-angiotensin-aldosterone: system of hormones that respond to decrease in blood volume and help maintain the correct blood volume. M. Zaharna Clin. Chem. 2009 12

13. Regulation of blood volume Changes in blood volume detected by receptors in: the cardiopulmonary circulation, carotid sinus, aortic arch and glomerular arterioles They activate effectors that restore volume by: appropriately varying vascular resistance, cardiac output, and renal Na and H 2 O retention. M. Zaharna Clin. Chem. 2009 13

14. M. Zaharna Clin. Chem. 2009 14 Angiotensin converting enzyme (ACE)

15. 15

16. Regulation of blood volume Other Factors effecting blood volume: 1. Atrial natriuretic Peptide (ANP) → sodium excretion → ↓ blood volume 2. Volume receptors → release of AVP → conserve water → ↑ blood volume 3. Glomerular filtration rate (GFR) ↑ in volume expansion and ↓ in volume depletion M. Zaharna Clin. Chem. 2009 16

17. Determination of Osmolality Serum or urine sample (plasma not recommended due to the use of anticoagulants) Based on properties of a solution related to the number of molecules of solutes per kilogram of solvent such as: Freezing point Vapor pressure M. Zaharna Clin. Chem. 2009 17

18. Determination of Osmolality Freezing Point Osmometer: Standardized method using NaCl reference solution. Specimen is supercooled to -7ºC, to determine freezing point. ↑ osmolality causes depression in the freezing point temp. More solutes present the longer the specimen will take to freeze. M. Zaharna Clin. Chem. 2009 18

19. Osmolal Gap Osmolal gap is the difference between the measured osmolality and the calculated one. Osmolal Gap= measured osmolality - calculated osmolality The osmolal gap indirectly indicates the presence of osmotically active substances other than sodium, urea or glucose. (ethanol, methanol or β -hydroxybutyrate) M. Zaharna Clin. Chem. 2009 19

20. M. Zaharna Clin. Chem. 2009 20

21. Sodium Most abundant extracellular cation- 90% Major function is maintaining the normal water distribution & osmotic pressure of plasma Role in maintaining acid-base balance (Na +, H + exchange mechanism) Normal range Serum:136-145 mmol/L ATPase ion pump: the way the body moves sodium and potassium in and out of cells. 3 Na + out of the cell for every 2 K + in and convert ATP to ADP. M. Zaharna Clin. Chem. 2009 21

22. Regulation of Sodium Balance Plasma Na + concentration depends: on the intake and excretion of water and, on the renal regulation of Na + Three processes are of primary importance: 1. intake of water in response to thirst (p. osmolality) 2. the excretion of water (AVP release) 3. the blood volume status, which affects Na + excretion through aldosterone, angiotensin II, and ANP (atrial natriuretic peptide). M. Zaharna Clin. Chem. 2009 22

23. Nephron 23

24. Regulation of Sodium Balance 70 % of sodium that is filtered is reabsorbed in proximal tubules. Remainder occurs in the ascending loop of Henle (without water absorption) & DCT under regulation of Aldosterone Renin-Angiotensin system Atrial natriuretic Peptide (ANP) → sodium excretion M. Zaharna Clin. Chem. 2009 24

25. Hyponatremia Defined as a serum/plasma level less than 135 mmol/L. One of the most common electrolyte disorders in hospitalized and non-hospitalized patients Levels below 130 mmol/L are clinically significant. M. Zaharna Clin. Chem. 2009 25

26. Hyponatremia M. Zaharna Clin. Chem. 2009 26

27. Hypernatremia Hypernatremia: increased sodium concentration > 145 mmol/l Result of excess water loss in the presence of sodium excess, or from sodium gain M. Zaharna Clin. Chem. 2009 27

28. Sodium determination Methods: 1. Flame emission spectrophotometry 2. Atomic absorption spectrophotometry 3. Ion Selective electrode M. Zaharna Clin. Chem. 2009 28

29. Atomic absorption spectrophotometry M. Zaharna Clin. Chem. 2009 29

30. Ion Selective electrode M. Zaharna Clin. Chem. 2009 30

31. Potassium Major intracellular cation 20 X greater concentration in the cell vs. outside. 2% of the bodies potassium circulates within the plasma. Function: Regulates neuromuscular excitability Hydrogen ion concentration Intracellular fluid volume M. Zaharna Clin. Chem. 2009 31

32. Effects on Cardiac muscle Ratio of K + intracellular & extracellular is important determinant of resting membrane potential across cell membrane Increase plasma potassium; decreasing the resting membrane potential, increase excitability, muscle weakness Decrease extracellular potassium; decrease excitability M. Zaharna Clin. Chem. 2009 32

33. Potassium Role in Hydrogen Concentration In hypokalemia (low serum K + ), As K + is lost from the body, Na + and H + move into the cell. The H + concentration is, therefore, decreased in the ECF, resulting in alkalosis. M. Zaharna Clin. Chem. 2009 33

34. Regulation of potassium The kidneys are important in the regulation of K + balance. Initially, the proximal tubules reabsorb nearly all the K +. Then, under the influence of aldosterone, K + is secreted into the urine in exchange for Na + in both the distal tubules and the collecting ducts. Thus, the distal tubule is the principal determinant of urinary K + excretion. Most individuals consume far more K + than needed; the excess is excreted in the urine but may accumulate to toxic levels if renal failure occurs. M. Zaharna Clin. Chem. 2009 34

35. Hypokalemia Decrease of serum potassium below 3.5 mmol/l M. Zaharna Clin. Chem. 2009 35

36. Hyperkalemia Increase potassium serum levels > 5 mmol/l Associated with diseases such as renal and metabolic acidosis M. Zaharna Clin. Chem. 2009 36

37. Potassium determination Assay method: Ion selective Electrode a valinomycin membrane is used to selectively bind K + M. Zaharna Clin. Chem. 2009 37

38. Chloride Major extracellular anion Cl – is involved in maintaining: osmolality, blood volume, and electric neutrality. In most processes, Cl – ions shift secondarily to a movement of Na + or HCO 3 –. Cl – ingested in the diet is Completely absorbed by the intestinal tract. M. Zaharna Clin. Chem. 2009 38

39. Chloride Cl – ions are filtered out by the glomerulus and passively reabsorbed, in Conjuction with Na, by the proximal tubules. Excess Cl – is excreted in the urine and sweat. Excessive sweating stimulates aldosterone secretion, which acts on the sweat glands to Conserve Na and Cl –. M. Zaharna Clin. Chem. 2009 39

40. Electric Neutrality Sodium/chloride shift maintains equilibrium within the body. 1. Na reabsorbed with Cl in proximal tubules. 2. Chloride shift In this process, carbon dioxide (CO 2 ) generated by cellular metabolism within the tissue diffuses out into both the plasma and the red cell. In the red cell, CO 2 forms carbonic acid (H 2 CO 3 ), which splits into H + and HCO 3 - (bicarbonate). Deoxyhemoglobin buffers H +, whereas the HCO 3 - diffuses out into the plasma and Cl - diffuses into the red cell to maintain the electric balance of the cell M. Zaharna Clin. Chem. 2009 40

41. Chloride shift 41

42. Hypochloremia Hypochloremia: < 98 mmol/l M. Zaharna Clin. Chem. 2009 42

43. Hypercholremia Hypercholremia: > 109 mmol/l M. Zaharna Clin. Chem. 2009 43

44. Assay 1. Coulometric titration (ref. method) 2. Ion selective electrode M. Zaharna Clin. Chem. 2009 44