9) Body water and electrolytes Flashcards
list main body cations
sodium
potassium
calcium
magnesium
trace elements
list main body anions
chloride
bicarbonate
proteins (albumin)
organic acids (lactate)
sulfate
phosphate
main intracellular ions
K+
phosphate
proteins
main extracellular ions
Na+
Cl-
HCO3-
proteins
Na+ functions
Maintains osmolality
Regulates acid-base balance by Na-H exchange in kidneys
K+ functions
Involved in heart and skeletal muscle contraction
Maintains intracellular osmolality
Influences acid-base balance
80% plasma osmolality is due to…
Na and Cl
chloride functions
Maintains plasma osmolality with sodium
Chloride shift (Maintains electroneutrality when Cl- exchanges with HCO3-)
Test used to diagnose children with Cystic Fibrosis
sweat chloride
> 60 mmol/L chloride is positive for…
CF
———- and the agent ——– is used to stimulate sweat production on the skin of a child
Iontophoresis
pilocarpine
how does hemolysis affect electrolyte measures?
Increased Potassium
Increased Phosphorus
Increased Iron
Increased Magnesium
Increased AST, ALT, CK, Troponin, and LD (liver & cardiac enzymes)
calculate anion gap
AG = [Na + K] - [Cl + HCO3]
or
AG = AG = Na - [Cl + HCO3]
causes of increased AG (not mudpiles)
- Renal Tubular Disease
- Diabetic Ketoacidosis
causes of low AG
- low albumin (most common)
- Organic paraproteins
- Inorganic bromide, lithium, Iodine, or Polymyxin B
MUDPILES
causes of high AG
- methanol
- uremia
- DM
- paraldehyde
- isoniazid
- lactic acidosis
- ethylene glycol/ethanol
- salicylate
major difference between plasma and ISF
presence of protein in plasma and virtually none in ISF
Represents a heterogeneous mixture of solutes that are difficult to measure directly because of the lack of cells free of contamination
intracellular water compartment
interactions of physical forces within and among fluid compartments
Gibbs-Donnan equilibrium
Used to identify the number of moles of a particle per kilogram of water, not the kind of particle
osmolality
Solution concentrations expressed on a weight factor are ——— independent
temperature
As osmolality increases…
- Osmotic pressure
- Boiling point
- Freezing point
- Vapor pressure
increases
increases
decreases
decreases
explain how the freezing point osmometer works
- Sample is rapidly supercooled to several degrees below its freezing point.
- Then agitated with the stirrer to initiate freezing.
- Rate at which this heat of fusion is released from the ice being rapidly formed reaches equilibrium with the rate of heat removed.
The freezing point is lowered by an amount that is directly proportional to…
the concentration of dissolved particles in the solution
osmolality equation
mOsm/kg = (1.86)(Na) + (Glucose/18) + (BUN/2.8) + 9
osmol gap
osmol gap = measured osm - calculated osm
the causes of high osmol gap and AG are basically the same, except…
salicylate poisoning does not cause high osmol gap
Pressure created in a solution by the presence of large (> 30 kDa) proteins, also called colloids.
colloid oncotic pressure
hypothalamus responds to these stimuli in order to regulate water balance
Increases in extracellular water osmolarity
Decreases in intravascular volume
Angiotensin II
angiotensin II effect on transport
increases NaCl and H2O reabsorption
aldosterone effect on transpoart
increases NaCl and H2O reabsorption
ANP, BNP, CNP effect on transport
inhibits NaCl and H2O reabsorption
urodilantin effect on transport
inhibits NaCl and H2O reabsorption
ADH effect on transport
Increases H2O reabsorption
Causes increased thirst and water intake
thirst center
Stimulates the posterior pituitary gland to secrete Antidiuretic Hormone (ADH)
antidiuretic center
2 areas of hypothalamus responding to low water
thirst center (water intake)
antidiuretic center (water output)
RAAS regulates…
Body sodium and water content
Arterial blood pressure
Potassium balance
proteolytic enzyme produced, stored, and secreted by juxtaglomerular cells of the kidneys
renin
angiotensin II functions
- Stimulation of aldosterone secretion by the adrenal cortex
- Arteriolar vasoconstriction, which increases blood pressure
- Stimulation of ADH secretion and thirst
- Enhancement of NaCl reabsorption by the proximal tubule
aldosterone functions
- Na+ reabsorption in the distal nephron of the kidneys
- Water reabsorption in the kidneys
- K+ excretion (secretion) by the kidneys
Low effective circulating blood volume can be sensed by baroreceptors located in the…
carotid sinus and aortic arch
3 natriuretic peptides
Atrial (A)-type natriuretic peptide (ANP)
Brain (B)-type natriuretic peptide (BNP)
(C)-type natriuretic peptide (CNP)
natriuretic peptides respond to…
intravascular volume expansion
Hormone produced primarily in atria
ANP
ANP functions
- Reducing the venous pressure that occurs with a given increase in blood volume
- Increasing vascular permeability
- Promoting natriuresis and diuresis
natriuresis
excretion of Na+ in urine
Hormone produced and stored in cardiac ventricles
BNP
Levels increase in Congestive Heart Failure
BNP
Produced in vascular endothelial cells, brain, and renal tubules
CNP
Potent venous dilator, but no natriuretic effect
CNP
In the brain, ANP inhibits….
salt appetite
water intake
secretion of ADH and corticotropin
conditions associated with dilutional hyponatremia
Weight gain & excess edema
Liver failure
Congestive heart failure
Renal failure
Nephrotic syndrome
Inappropriate ADH secretion
hyponatremia causes
v/d
polyuria
hypernatremia causes
Ingestion of large amounts of sodium salts
Administration of hypertonic NaCl Hyperaldosteronism
Excessive sweating
DI
Osmotic diuresis
Small amount is taken up by cells and most excreted by the kidneys
K+
hyperkalemia s/s
Mental confusion
Weakness
Tingling sensations
Flaccid paralysis of the extremities
Respiratory muscle weakness
causes of pseudohyperkalemia
Hemolysis
Leukocytosis
Vigorous arm exercise
Tight application of tourniquet
Squeezing the area around a draw site
causes of hyperkalemia
High-potassium uptake
Decreased K+ excretion
Crush injuries
Digitals overdose
Tissue hypoxia
Metabolic acidosis
causes of hypokalemia
Metabolic alkalosis
Diuretic administration
Increased GI loss
Increased urinary loss
Metabolic ——– is often associated with hyperkalemia because potassium moves out of the cell and into the extracellular water space.
acidosis
Metabolic ——- is a condition characterized by hypokalemia. Potassium ions move from the extracellular water space and into the cell.
alkalosis
causes of hyperchloremia
Dehydration
Kidney diseases
Salicylate intoxication
causes of hypochloremia
Vomiting
Salt-losing nephritis
Metabolic acidosis
Decreased secretion of Cortisol and Aldosterone
Causes water and Na loss by kidneys
Addison’s disease
diuretics used to tx…
conditions that have fluid retention (also called edema) as a symptom, such as heart failure, kidney failure and cirrhosis of the liver
Characterized by polyuria accompanied by polydipsia because of ADH deficiency
DI
central vs nephrogenic DI
Central DI is caused by a failure of the pituitary gland to secrete normal amounts of A D H in response to osmoregulatory factors.
Nephrogenic DI patients have renal resistance to the action of ADH. Still producing ADH, but just not receptive to it.
DI s/s
Increased urine output >2.5L/day
Low urine specific gravity, low urine osmolality
Crave water/ice
Extreme fatigue, muscle pain/weakness
Increased serum osmolality, hypernatremia
causes of DI
- Kidneys not receptive to ADH
- Damage to the pituitary gland and/or hypothalamus
- Brain trauma through stroke or head trauma
- Tumors
- Drugs (demenocycline)
- Gestational due to the placenta producing vasopressinase
parts of DI dx
polyuria
urine glucose testing to exclude glycosuria
measurement of urine and serum creatinine, electrolytes, and osmolality
A water-deprivation test is useful to distinguish central from nephrogenic DI
water deprivation test is d/c if…
urine osmolality rises above 500 or if the patient loses more than 3% of body weight, without a rise in urine osmolality
goal of DI therapy
urine osmolality up
urine output down
A chronic, excessive intake of water suppresses ADH secretion and produces hypotonic polyuria
Psychogenic or Primary Polydipsia
The increased production of ADH in the absence of known stimuli for its release
syndrome of inappropriate ADH secretion
SIADH s/s
Low serum osmolality
Normal to increased plasma volume
Fluid overload (weight gain)
Hypotonic (low osmotic pressure) plasma and urine
Hyponatremia, with continued sodium excretion
Low urine output with high specific gravity and increased urine osmolality
—— is suspected if urine osmo > plasma osmo without corresponding low urine Na
SIADH
tx for moderate SIADH
Loop Diuretics (Lasix)
Hypertonic IV solutions (3% Saline)
tx for severe SIADH
Demeclocycline
water overload —ADH, water, serum osmo, serum Na, urine output, urine osmo
ADH—
water ↑
serum osmo ↓
serum Na ↓
urine output ↑
urine osmo ↓
DI — ADH, water, serum osmo, serum Na, urine output, urine osmo
ADH↓
water ↓
serum osmo ↑
serum Na ↑
urine output ↑
urine osmo ↓
SIADH —ADH, water, serum osmo, serum Na, urine output, urine osmo
ADH↑
water ↑
serum osmo ↓
serum Na ↓
urine output ↓
urine osmo ↑
suspect ingestion if osmo gap…
> 25
causes of high osmo gap without high AG
- isopropyl alcohol
- mannitol
- sorbitol
- glycine
- maltose
cannot be used as an anticoag for electrolyte specimens
sodium heparin
Lipemic samples can interfere with…
Sodium falsely decreased due to…
indirect ISE measurement
electrolyte exclusion effect
ISE
ion-selective electrode
direct vs indirect ISE
direct —no dilution
indirect —sample diluted
electrolyte instruments account for —% solid portion of plasma
7%
4 methods of measuring Na+
Both direct and indirect ISEs
Flame-emission spectroscopy (obsolete)
Atomic-absorption spectroscopy
Spectrophotometry
extra K+ in serum (compared to plasma) is mainly a result of…
platelet rupture during coagulation
0.1-0.7 mEq/L lower
Slight hemolysis can raise K+ vales —-%, marked hemolysis —%, and gross hemolysis —–%
3
12
30
incorporates valinomycin into its organic liquid membrane
ISE for K+
Macroduct coils
used to collect sweat
