Electrolytes

electrolyte

ions capable of carrying an electrical charge

extracellular fluid

water outside the cell

interstitial fluid, plasma, lymph fluid, cerebrospinal fluid

intracellular fluid

fluid inside the cells

osmolality

a measure of the number of dissolved particles in a solution (mmol/kg solvent)

osmolal gap

the difference between the measure and calculated osmolality

indirectly indicates the presence of osmotically active substances other than sodium, urea, or glucose

anion

negatively charged ions that move toward the anode

cation

positively charged ions that move toward the cathode

electroneutrality

cations = anions

aldosterone

main electrolyte regulating hormone produced by the adrenal gland

regulates sodium absorption and salt/water balance in kidneys

renin-angiotension systems

regulates aldosterone

renin

enzyme produced by kidney in response to decreased blood volume of blood pressure

angiotensinogen

liver globulin acted on by renin to produce angiotensin I

angiotensin I

precursor to angiotensin II

angiotensin II

causes vasoconstriction which quickly increases blood pressure and secretion of aldosterone

antidiuretic hormone (ADH)

secretion by pituitary acts on kidney to increase water reabsorption

hypernatremia

elevate levels of sodium in blood

caused by excess water loss, decreased water intake, increased sodium intake

sweat chloride

increased levels in sweat tests used to dx cystic fibrosis

bicarbonate (HCO3-)

second most abundant anion in ECF

total CO2 (TCO2)

composed of bicarbonate ion, carbonic acid, and dissolved CO2

anion gap

balance between cations and anions

urine electrolytes

Ca, Cl, K, Na

atomic absorption

method to analyze calcium levels

ion-selective electrodes (ISE)

common method used to quantitate sodium, potassium and chloride

freezing point depression

the temperature at which the vapor pressures of the solid and liquid phases are the same

osmometer

lab instrument used to measure osmolality

why does the body need to balance water and electrolytes

water is the solvent for all processes in the human body

total body water

2/3 = ICF

1/3 = ECF

major ECF cation

sodium

major ICF cation

potassium

major ECF anion

chloride

major intracellular anion

phosphate

importance of osmotic pressure

the pressure allows solvent to flow through a membrane to establish equilibrium between compartments of different osmolality

major contributors that determine osmotic pressure

solutes and solvents

major contributors to osmolality

thirst (deceases plasma osmolality) and secretion of ADH (increases water reabsorption)

serum reference range for osmolality

275 - 295 mOsm/kg

osmolality formula

1.86Na + glucose/18 + BUN/2.8 + 9

how to measure osmolality

freezing point depression or vapor pressure osmometers

major cations of the body

Na, K, Ca, Mg, Fe, Cu, Mn, Co, Cd, Cr, Zn

major anions of the body

Cl, HCO3, PO4, SO4, Br, I, organic acids, proteinate

renin-angiotensin-aldosterone system function

to maintain blood pressure and ensure good perfusion to all tissues

another name for ADH

arginine vasopressin hormone

why is the measurement of urine electrolytes of limited value

the kidney is central to the regulation and conservation of electrolytes in the body and many factors can influence urinary electrolyte excretion

specimen for urine electrolyte measurement

24-hour timed urine

reference ranges for 24 hour urine sodium and potassium

K: 25-125 mmol/day

Na: 40-220 mmol/day

analytical/reference method for measuring Na and K concentrtions

ISE

specimens used to measure K and Na concentrations

serum, heparinized plasma, urine

how does hemolysis effect Na and K concentrations

Na: no effect

K: falsely elevates

analytical methods to measure Cl concentrations

ISE

chloride concentration specimen

serum, heparinized plasma, 24 hr urine, sweat

TCO2 specimens

serum, heparinized plasma