4 Electrolytes and Osmometry

• Helps transport nutrients. • Used to removes waste products via urination. • Regulates body temperature through sweating. 40-75% of your total body weight is water.

• Charged minerals that help to control the body’s fluid (osmotic pressure & water) and acid-base balance. • Connected to muscle and nerve activity, heart rhythm, etc. • Oxidation-reduction reactions and enzyme cofacters. Common electrolytes include Na+, k+, Cl- TCO2 (or HCO3-).

Hypothalamus in response to increased plasma osmolality.

ADH (antidiuretic hormone) and aldosterone action in the kidney. • ADH causes the kidneys to reabsorb water, decrease urine. • Aldosterone conserves Na+ and Cl- levels in bloodstream (water follows and gets retained in body) and promotes the elimination of K in urine. Overall plasma osmolality starts to return normal (as well as blood volume and pressure) until ADH and aldosterone are suppressed.

Intracellular Fluid –> 2/3 of total body water (inside cells) Extracellular Fluid –> 1/3 remaining. Includes interstitial fluid spaces, plasma, lymph, GI fluids, synovial fluids, pleural fluids, CSF, etc. Separated by semipermeable membranes.

Controlled by maintaining concentrations of electrolytes and proteins in individual compartments (cells) using these three modes: • Active Transport - ATP (energy) moves solutes from low to high concentration areas • Passive Diffusion - Solutes move from high to low concentration without energy input. Random. • Osmosis - semipermeable membrane allows water (not solutes) to move from low osmotic pressure to areas of high osmotic pressure. No energy input.

Lithium heparin anticoagulant tubes (used most often). Precautions: • Sodium heparin anticoagulant will falsely increase Na values. • Avoid hemolysis & separate cells from plasma/serum ASAP. • Intracellular K+ will be released into plasma/serum. Falsely increases results. • Samples for ionized calcium must remained unopened.

May need 24 hour collection. A 100 mL random sample may be acceptable.

Strenuous exercise can cause potassium values to be increased as much as 20%.

Sodium - Adult Plasma 135-147 mmol/L Urine 40-200 mmol/d

Potassium - Adult: Plasma 3.5 - 5.1 mmol/L Urine 40-80 mmol/d

Chloride - Adult: Plasma 97-106 mmol/L Urine 110-250 mmol/d

Total Carbon Dioxide (CO2) 22-30 mmol/L

Total Calcium - Adult: Plasma 2.10 - 2.60 mmol/L

Plasma samples - adults: Glucose 3.6-6.0 mmol/L Albumin - 33-45 g/L Urea 2.8 - 7.1 mmol/L

Sodium functions: • Maintains a) fluid distribution b) Osmotic pressure • Role in nerve and muscle function. Recall that Na went through the channels that were opened ACh in the NMJ then traveled as a muscle action impulse! Plus it operates in nerves as a voltage gated channel.

Imbalances in Sodium –> Can lead to brain swelling and coma.

Clinical: • Acid base balance, water balance. • Dehydration. • Renal threshold 110-120 mmol/L.

Potassium (K+): • Nerve impulse transmission • Muscle contractility. Recall that when a nerve impulse depolarizes (charge goes up), K+ channels open to bring the signal back down to repolarize.

• Electrolyte imbalance. • Muscle weakness • Cardiac arrhythmia. • renal failure • Hemolysis falsely increases lab value.

• Maintains fluid balance with Na+ • Cl- values change with Na+ (i.e. NaCl, salt) • Acid-base regulation.

• Sweat chloride test is used to detect cystic fibrosis. • Stomach is unable to secrete digestive enzyme • Acid base balance, water balance and dehydration. Note: re2 in ppt she said it was pancreas.

• Acid base regulation • Released and reabsorbed by kidneys to maintain pH • Electrical neutrality. 4 Chloride shift • Transport of CO2 (via HCO3- and that acid/base equation with carbonate.)

Total CO2: • Acid base imbalance in respiratory & metabolic systems. • Increased TCO2 in metabolic alkalosis. • Decreased TCO2 in metabolic acidosis.