Final Exam

Electrolyte are
solutions containing free ions behaving as electrically conductive media. Because they consist of ions in solution, electrolytes are ionic solutions
Electrolyte solutions are formed when
a salt is placed into a solvent and the individual components dissociate
Electrolytes are classified
based on their migration in and electrical field.
Cations migrate towards
the cathode and are said to be positively charged.
The principle cations in human plasma are
Na+, K+ Ca++, MG++
Anion migrate towards
the anode and are said to be negatively charged.
The principle anions in human plasma are
CL-, HCO3-, So4-,PO4-
Total body water
includes the water within and outside the cell and that normally found in the gastrointestinal and urogential systems
Total body water is subdivided into two compartments:
the intracellular fluid (ICF) and the extracellular fluid (ECF)
is the medium for all metabolic exchange
medium for cellular metabolic reactions
Average total body water
Total body water varies inversely with
total body fat
Plasma volume is
the sole compartment of total body water
Plasma volume percent of total body weight
Total body water as a percentage of body weight decreases
during intrauterine development and reaches the normal adult values by age three.
Plasma volumes remain
constant throughout life
The absolute volume of the water compartments
all increase with growth.
Plasma is
mixture of water and macromolucules, i.e., proteins, lipids.
Plasma water refers strictly
to the aqueous phase
The concentration of ions in the plasma is
lower than their actual concentration in the plasma water.
The ions are present solely in the
water phase
Reported concentrations represent
the ion concentration in the plasma
The actual concentration of the ions in the plasma water impact
diffusion across the capillary membrane.
Increased concentrations of macromolecules in the plasma will result in
lower measured ion concentration even though plasma water ion concentrations and activity may be normal.
Donnan’s equilibrium
requiring that the sum of all charged particles must be equal.
the sum of the cations must
equal the sum of the anions so no net electrical charge exists
Anion Gap
The sum of the measured cations (Na+ +K+) exceeds the sum of the measure anions (CL- + HCO3-).
Anion gap indicates
unmeasured anions are greater than the unmeasured cations.
Increases in the anion gap usually indicates
an increase in one or more of the unmeasured anions. Used in the differential diagnosis of metabolic acidosis
Anion gap formula
[Na+] – [Cl-] – [HCO3-]
Reference range Anion Gap
8 to 16 mmol/l
Major Clinical Uses of the Anion Gap
To signal the presence of a metabolic acidosis
Help differentiate between causes of a metabolic acidosis: high anion gap versus normal anion gap metabolic acidosis.
In an inorganic metabolic acidosis
the infused Cl- replaces HCO3 and the anion gap remains normal.
In an organic acidosis
the lost bicarbonate is replaced by the acid anion which is not normally measured. This means that the AG is increased
Major functions of blood electrolytes
Maintenance of osmotic pressure
Water distribution
Maintenance of pH
Regulation of the proper function of the heart and muscles
Oxidation-reduction reaction – electron transfer
Catalytic reactions by serving as cofactors for enzymes
Theoretical Osmotic Pressure
O.P. (t) (mmHg) = 19.3 mmHg/mOsm/L X Osmolality (mOsm/L)
Theoretical osmotic pressure is proportional
to osmolality.
Osmotic pressure is
the force that tends to move water from dilute solutions to concentrated solutions
effective osmotic pressure
When a membrane is permeable to a solute the solute exerts no osmotic pressure across the membrane
The effective osmotic pressure is dependent upon
the total number of solute particles in solution and the permeability of the membrane to the solute
The higher the permeability of the membrane to the solute
the lower is the effective osmotic pressure of a solution of that solute at any given osmolality.
Measurements of osmolality measure the
theoretical not the effective osmotic pressure
A solution with an effective osmotic pressure greater than plasma
A solution with a theoretical osmotic pressure greater than plasma
Hyposmotic and hypotonic
refer to solutions with effective and theoretical osmotic pressures less than plasma.
colloid osmotic pressure.
The effective osmotic pressure of plasma and the interstitial fluid across the capillary membrane
Capillary endothelium are impermeable to
larger protein molecules (colloids).
These colloids are responsible for
the effective osmotic pressure between the plasma and the interstitial fluid
Water distribution across the capillary endothelial membrane are controlled by
the balance between filtration and reabsorption forces
The principle filtration force in the plasma is
hydrostatic pressure the primary reabsorption force is the colloid osmotic pressure.
Plasma hydrostatic pressure drive water
colloid osmotic pressure draws water
Hydrostatic Pressure
is the pressure that the fluid exerts on the walls of its container. In human body, the hydrostatic pressure refers to the pressure that the blood exerts on the walls of the arteries and veins.
Osmotic Pressure
is the pressure required to prevent the flow of water across a semi permeable membrane via osmosis.
Water and solute distribution across the cell membrane depend on
on the integrity of the cell membrane and on osmotic and electrochemical forces
The permeability of the cell membrane to a solute is directly related to
the lipid solubility of the solute and inversely related to hydrophilicity and molecule size
Extracellular osmolality is maintained between
285 and 300 mOsm/L through the balance between water intake an excretion.
Water intake
Ingestion, Water in foodstuffs and Oxidative metabolism
Water Loss
Urine, Insensible Perspiration and GI water loss (stool)
Kidney is principally responsible for
regulating the volume and composition of the body fluids
Insensible Water Loss
Occurs through the skin and the respiratory tract
Insensible Water Loss varies directly with
ambient temperature, body temperature and activity
Insensible Water Loss varies inversely with
ambient humidity
simple dehydration
Defined as decrease in total body water with a relatively normal total body sodium
simple dehydration results from
failure to replace obligatory water losses, regulatory failures
simple dehydration associated with
hypernatremia and hyperosmolarity because water balance is negative and sodium balance is normal
^ECF osmolality as water is lost results in
movement of water out of the ICF. Results in a contraction of both the ECF and the ICF.
Dehydration due to Water and Sodium Loss
Most often dehydration involves a net negative balance in both water and sodium
Hypernatremic (hyperosmolar) dehydration
water balance is more negative than sodium, most common
Normonatremic (isoosmolar) dehydration
water and sodium balance are equally negative
Hyponatremic (hypoosmolar) dehydration
water balance is less negative than sodium balance
Hypernatremic (hyperosmolar) dehydration Changes to Extracellular Volume
ECF volumes effected the least. ^ECF Osm. Draws water from the ICF – ICF contracts
Normonatremic (isoosmolar) dehydration Changes to Extracellular Volume
no change to ECF Osm – no net water flow
Hyponatremic (hypoosmolar) dehydration
Changes to Extracellular Volume
Greatest effect to ECF volume – vOsm. Of ECF causes water to move into the cells – ICF volume expanded
Water intoxication
Defined as increased total body water
Water intoxication usually results from
impaired renal excretion resulting from excessive ADH secretion
Water intoxication usually results in
hyponatremia and hypoosmolality producing a expansion of the ECF and ICF
If Na is normal the ^ in total body water
water is confined to the EC
If Na is vthan the increase in water is
shared between the ECF and ICF.
Gibbs-Donnan equilibrium
difference in Na concentration between the ECF and the ISF
Sodium balance is a result of
carefully controlled intake and output mechanisms
Sodium intake
food stuffs
Sodium output
occurs through three primary routes: GI tract, skin, and urine
Sodium concentration in sweat is decreased by
Sodium concentration in sweat is increased by
cystic fibrosis
Sodium Loss through the skin can be extensive in
severe burns and exudative skin lesions
The principle route for sodium excretion
Renal excretion regulated through
Management of Na+ reabsorption in the distal tubule
establishes the renal threshold for Na+ – 110mM/L which determine the amount of Na+ excreted in the urine.
Sodium Depletion
Occurs when the output of sodium exceeds intake
Indicates a decreased plasma sodium concentration
Hyponatremia- Causes
Sodium deficit greater than water deficit, Fluid Shift – ECF to ICF, Psuedohyponatremia, Water excess greater than sodium excess
Occurs when sodium intake exceeds sodium output usually because of a defect in the homeostatic mechanism
Hypernatremia- conditions
Cardiac Failure, Liver Disease, Renal Disease (nephrotic syndrome), Hyperaldosteronism, Pregnancy, CHF
Hypernatremia – Causes
Sodium excess greater than water excess, Water deficits greater than sodium deficits, Hyperventilation, Diabetes insipidus, Osmotic diuresis, Diminished fluid input – diminished thirst, Essential hypernatremia, Certain diarrheal states and vomiting
Specimen for sodium determinations
serum, plasma whole blood sweat, urine, feces, GI fluids
Factors that increase cellular influx of K+
Insulin, aldosterone, alkalosis, ? adrenergic stimulation
Factors that decrease cellular influx of K+
Acidosis, alpha adrenergic stimulation, tissue hypoxia
K+ input
K+ output
GI Tract
Factors regulating distal tubular secretion of K+ include
Intake of Na+ and K+
Water flow rate in the distal tubules
Plasma levels of mineralocorticoids
Acid-base status
Increased K+ levels produce
symptoms of mental confusion, weakness, numbness and tingling in the extremities, slowed heart rate, peripheral vascular collapse and cardiac arrest.
K+ excess
+ levels greater than 7.5 mM/L, <10.0 is fatal
Increased potassium intake
Diet, Oral supplementation, IV administration, High dose potassium penicillin use, transfusion
Decreased potassium excretion
Renal Failure, Adrenal failure (hypoaldosteronism), diuretics that block distal K+ secretion (spironolactone), Primary defects in renal tubular handling of K+ secretion.
Causes K+ depletion
Decreased potassium intake, Increased GI Loss, Increased urinary loss
Occurs with an increased plasma K+ concentration
Occurs with decrease plasma K+ concentrations
Hyperkalemia – Causes
Pseudohyperkalemia, Intracellular to extracellular shifts, High potassium intake, and Decreased potassium excretion
Hypokalemia – Causes
Extracellular to intracellular K+ Shift, Decreased potassium intake, Increased GI Loss, and Increased urinary loss
Specimens for the determination of K+
serum or plasma must avoid hemolysis.
Major anion of the extracellular fluid
Output of Cl-GI tract, skin, urine
occurs through three principle routes:
GI tract, skin, urine
Chloride Excess
Accumulation occurs when intake exceeds output because of some abnormality n homeostatic mechanism
Chloride Depletion
Occurs when output exceeds intake

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