Water, Sodium, Potassium

major cation contributor to osmolality in the ECF

sodium

sodium serum normal range

135-145 mmol/L

sodium renal threshold

110-130 mmol/L

why does urea not have an effect on water distribution?

it diffuses freely across membranes

• still affects osmolality

osmolality equation

(1.86 x Na) + (glucose/18) + (BUN/2.8) + 9

most cell membranes are _________ to sodium and the gradient is maintained by ______-__________ _____

impermeable; sodium-potassium pump

sodium retention is controlled by—

aldosterone

sodium excretion is controlled by—

natriuretic peptide hormones

ANP (atrial natriuretic peptide)

inhibits Na reabsorption, inhibits renin release, suppresses norepi and angiotensin II

• released in response to cardiac atria expansion because of fluid expansion

BNP (beta-type natriuretic peptide)

similar to ANP and secreted by cardiac ventricles upon expansion

• congestive heart failure marker

CNP (C-type natriuretic peptide)

present in vascular endothelium

• works as a vasodilator to decrease blood pressure

major cation contributor to osmolality in the ICF

potassium

potassium serum normal range

3.5-5.0 mmol/L

potassium renal threshold

no renal threshold

major function of potassium

contraction of skeletal and cardiac muscles

• imbalance = heart arrythmia

during clotting, platelets release________ leading to—

potassium, increase in serum potassium 0.2-0.3 mmol/L higher than plasma

osmolarity is—

number of osmoles per liter (Osm/L)

osmolality is—

the measurement of the number of dissolved particles in a solution

• mOsm/kg

serum osmolality normal range

275-295 mOsm/kg

• >295 = dehydrated

• <275 = overhydrated

normal urine osmolality in 24 hour collection

301-1090 mOsm/kg

urine osmolality is used to assess—

electrolyte fluid balance and kidney’s ability to concentrate urine

colligative properties

freezing point depression and boiling point elevation

osmometry

method of measurement of osmolality using urine or serum

freezing point depression osmometry cannot use samples that—

are high viscosity or high molality

boiling point depression osmometry cannot use samples that—

are highly volatile

osmolal gap

difference between measure osmolality and calculated osmolality

osmolal gap equation

measured - calculated

osmolal gap normal range

<10-15 mOsm/kg

osmolal gap greater than 10-15 mOsm/kg indicates

presence of unmeasured anions or SLUMPED

SLUMPED osmolal gap causes

• Salicylate intoxication (aspirin)

• Lactic acidosis

• Unmeasured anions

• Methanol, ethanol, alcohol

• Poisoning

• Ethylene glycol (antifreeze)

• Diabetic ketoacidosis (b-hydroxybutyrate presence)

normal response for decreasing blood volume

• increase in aldosterone

• significant increase in ADH

water excess is typically due to—

impaired water excretion

excessive intake in water can lead to—

water intoxication (psychiatric disorder)

• can lead to cerebral overhydration

sodium excess may be due to—

increased intake or decreased excretion leading to edema (water follows Na⁺)

hyponatremia

low Na⁺ in blood

depletional hyponatremia causes—

true loss of total body Na⁺

depletional hyponatremia can be caused by—

• diuretic overuse

• low aldosterone (Addison’s)

• diarrhea/vomiting

• severe burns/trauma

• sick cell syndrome (acute/chronic)

dilutional hyponatremia causes—

relatively low sodium because of increased water volume (overhydration)

dilutional hyponatremia can be caused by—

• overhydration

• SIADH

• hyperglycemia

• CHF

• liver cirrhosis

• nephrotic syndrome

falsely decreased sodium

same with high protein/lipids if using indirect ion selective

hypernatremia

increased Na⁺ in blood

causes of hypernatremia

• diarrhea (lose water 1st, electrolytes next)

• diabetes insipidus

• hyperaldosteronism

• cushing’s syndrome

diabetes insipidius

deficiency in ADH release

hyperaldosteronism

sodium and water retention

• 1^o - conn syndrome at adrenal gland

• 2^o - renin-angiotensin disorder

cushing’s syndrome

excessive production of ACTH

• stimulates adrenal to release aldosterone