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Electrolyte are

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solutions containing free ions behaving as electrically conductive media. Because they consist of ions in solution, electrolytes are ionic solutions

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Electrolyte solutions are formed when

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a salt is placed into a solvent and the individual components dissociate

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Electrolytes are classified

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based on their migration in and electrical field.

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Cations migrate towards

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the cathode and are said to be positively charged.

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The principle cations in human plasma are

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Na+, K+ Ca++, MG++

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Anion migrate towards

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the anode and are said to be negatively charged.

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The principle anions in human plasma are

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CL-, HCO3-, So4-,PO4-

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Total body water

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includes the water within and outside the cell and that normally found in the gastrointestinal and urogential systems

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Total body water is subdivided into two compartments:

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the intracellular fluid (ICF) and the extracellular fluid (ECF)

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ECF

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is the medium for all metabolic exchange

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ICF

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medium for cellular metabolic reactions

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Average total body water

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65%

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Total body water varies inversely with

answer

total body fat

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Plasma volume is

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the sole compartment of total body water

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Plasma volume percent of total body weight

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5%

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Total body water as a percentage of body weight decreases

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during intrauterine development and reaches the normal adult values by age three.

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Plasma volumes remain

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constant throughout life

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The absolute volume of the water compartments

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all increase with growth.

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Plasma is

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mixture of water and macromolucules, i.e., proteins, lipids.

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Plasma water refers strictly

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to the aqueous phase

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The concentration of ions in the plasma is

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lower than their actual concentration in the plasma water.

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The ions are present solely in the

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water phase

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Reported concentrations represent

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the ion concentration in the plasma

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The actual concentration of the ions in the plasma water impact

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diffusion across the capillary membrane.

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Increased concentrations of macromolecules in the plasma will result in

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lower measured ion concentration even though plasma water ion concentrations and activity may be normal.

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Donnan’s equilibrium

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requiring that the sum of all charged particles must be equal.

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the sum of the cations must

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equal the sum of the anions so no net electrical charge exists

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Anion Gap

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The sum of the measured cations (Na+ +K+) exceeds the sum of the measure anions (CL- + HCO3-).

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Anion gap indicates

answer

unmeasured anions are greater than the unmeasured cations.

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Increases in the anion gap usually indicates

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an increase in one or more of the unmeasured anions. Used in the differential diagnosis of metabolic acidosis

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Anion gap formula

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[Na+] - [Cl-] - [HCO3-]

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Reference range Anion Gap

answer

8 to 16 mmol/l

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Major Clinical Uses of the Anion Gap

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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.

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In an inorganic metabolic acidosis

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the infused Cl- replaces HCO3 and the anion gap remains normal.

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In an organic acidosis

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the lost bicarbonate is replaced by the acid anion which is not normally measured. This means that the AG is increased

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Major functions of blood electrolytes

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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

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Theoretical Osmotic Pressure

answer

O.P. (t) (mmHg) = 19.3 mmHg/mOsm/L X Osmolality (mOsm/L)

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Theoretical osmotic pressure is proportional

answer

to osmolality.

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Osmotic pressure is

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the force that tends to move water from dilute solutions to concentrated solutions

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effective osmotic pressure

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When a membrane is permeable to a solute the solute exerts no osmotic pressure across the membrane

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The effective osmotic pressure is dependent upon

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the total number of solute particles in solution and the permeability of the membrane to the solute

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The higher the permeability of the membrane to the solute

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the lower is the effective osmotic pressure of a solution of that solute at any given osmolality.

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Measurements of osmolality measure the

answer

theoretical not the effective osmotic pressure

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hyperosmotic

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A solution with an effective osmotic pressure greater than plasma

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hypertonic

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A solution with a theoretical osmotic pressure greater than plasma

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Hyposmotic and hypotonic

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refer to solutions with effective and theoretical osmotic pressures less than plasma.

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colloid osmotic pressure.

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The effective osmotic pressure of plasma and the interstitial fluid across the capillary membrane

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Capillary endothelium are impermeable to

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larger protein molecules (colloids).

question

These colloids are responsible for

answer

the effective osmotic pressure between the plasma and the interstitial fluid

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Water distribution across the capillary endothelial membrane are controlled by

answer

the balance between filtration and reabsorption forces

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The principle filtration force in the plasma is

answer

hydrostatic pressure the primary reabsorption force is the colloid osmotic pressure.

question

Plasma hydrostatic pressure drive water

answer

out

question

colloid osmotic pressure draws water

answer

in

question

Hydrostatic Pressure

answer

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.

question

Osmotic Pressure

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is the pressure required to prevent the flow of water across a semi permeable membrane via osmosis.

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Water and solute distribution across the cell membrane depend on

answer

on the integrity of the cell membrane and on osmotic and electrochemical forces

question

The permeability of the cell membrane to a solute is directly related to

answer

the lipid solubility of the solute and inversely related to hydrophilicity and molecule size

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Extracellular osmolality is maintained between

answer

285 and 300 mOsm/L through the balance between water intake an excretion.

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Water intake

answer

Ingestion, Water in foodstuffs and Oxidative metabolism

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Water Loss

answer

Urine, Insensible Perspiration and GI water loss (stool)

question

Kidney is principally responsible for

answer

regulating the volume and composition of the body fluids

question

Insensible Water Loss

answer

Occurs through the skin and the respiratory tract

question

Insensible Water Loss varies directly with

answer

ambient temperature, body temperature and activity

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Insensible Water Loss varies inversely with

answer

ambient humidity

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simple dehydration

answer

Defined as decrease in total body water with a relatively normal total body sodium

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simple dehydration results from

answer

failure to replace obligatory water losses, regulatory failures

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simple dehydration associated with

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hypernatremia and hyperosmolarity because water balance is negative and sodium balance is normal

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^ECF osmolality as water is lost results in

answer

movement of water out of the ICF. Results in a contraction of both the ECF and the ICF.

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Dehydration due to Water and Sodium Loss

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Most often dehydration involves a net negative balance in both water and sodium

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Hypernatremic (hyperosmolar) dehydration

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water balance is more negative than sodium, most common

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Normonatremic (isoosmolar) dehydration

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water and sodium balance are equally negative

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Hyponatremic (hypoosmolar) dehydration

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water balance is less negative than sodium balance

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Hypernatremic (hyperosmolar) dehydration Changes to Extracellular Volume

answer

ECF volumes effected the least. ^ECF Osm. Draws water from the ICF – ICF contracts

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Normonatremic (isoosmolar) dehydration Changes to Extracellular Volume

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no change to ECF Osm – no net water flow

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Hyponatremic (hypoosmolar) dehydration
Changes to Extracellular Volume

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Greatest effect to ECF volume - vOsm. Of ECF causes water to move into the cells – ICF volume expanded

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Water intoxication

answer

Defined as increased total body water

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Water intoxication usually results from

answer

impaired renal excretion resulting from excessive ADH secretion

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Water intoxication usually results in

answer

hyponatremia and hypoosmolality producing a expansion of the ECF and ICF

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If Na is normal the ^ in total body water

answer

water is confined to the EC

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If Na is vthan the increase in water is

answer

shared between the ECF and ICF.

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Gibbs-Donnan equilibrium

answer

difference in Na concentration between the ECF and the ISF

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Sodium balance is a result of

answer

carefully controlled intake and output mechanisms

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Sodium intake

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food stuffs

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Sodium output

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occurs through three primary routes: GI tract, skin, and urine

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Sodium concentration in sweat is decreased by

answer

aldosterone

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Sodium concentration in sweat is increased by

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cystic fibrosis

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Sodium Loss through the skin can be extensive in

answer

severe burns and exudative skin lesions

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The principle route for sodium excretion

answer

Kidney

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Renal excretion regulated through

answer

aldosterone

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Management of Na+ reabsorption in the distal tubule

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establishes the renal threshold for Na+ - 110mM/L which determine the amount of Na+ excreted in the urine.

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Sodium Depletion

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Occurs when the output of sodium exceeds intake

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Hyponatremia

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Indicates a decreased plasma sodium concentration

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Hyponatremia- Causes

answer

Sodium deficit greater than water deficit, Fluid Shift – ECF to ICF, Psuedohyponatremia, Water excess greater than sodium excess

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Hypernatremia

answer

Occurs when sodium intake exceeds sodium output usually because of a defect in the homeostatic mechanism

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Hypernatremia- conditions

answer

Cardiac Failure, Liver Disease, Renal Disease (nephrotic syndrome), Hyperaldosteronism, Pregnancy, CHF

question

Hypernatremia – Causes

answer

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

question

Specimen for sodium determinations

answer

serum, plasma whole blood sweat, urine, feces, GI fluids

question

Factors that increase cellular influx of K+

answer

Insulin, aldosterone, alkalosis, ? adrenergic stimulation

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Factors that decrease cellular influx of K+

answer

Acidosis, alpha adrenergic stimulation, tissue hypoxia

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K+ input

answer

food

question

K+ output

answer

GI Tract
Sweat
Urine

question

Factors regulating distal tubular secretion of K+ include

answer

Intake of Na+ and K+
Water flow rate in the distal tubules
Plasma levels of mineralocorticoids
Acid-base status

question

Increased K+ levels produce

answer

symptoms of mental confusion, weakness, numbness and tingling in the extremities, slowed heart rate, peripheral vascular collapse and cardiac arrest.

question

K+ excess

answer

+ levels greater than 7.5 mM/L, <10.0 is fatal

question

Increased potassium intake

answer

Diet, Oral supplementation, IV administration, High dose potassium penicillin use, transfusion

question

Decreased potassium excretion

answer

Renal Failure, Adrenal failure (hypoaldosteronism), diuretics that block distal K+ secretion (spironolactone), Primary defects in renal tubular handling of K+ secretion.

question

Causes K+ depletion

answer

Decreased potassium intake, Increased GI Loss, Increased urinary loss

question

Hyperkalemia

answer

Occurs with an increased plasma K+ concentration

question

Hypokalermia

answer

Occurs with decrease plasma K+ concentrations

question

Hyperkalemia – Causes

answer

Pseudohyperkalemia, Intracellular to extracellular shifts, High potassium intake, and Decreased potassium excretion

question

Hypokalemia – Causes

answer

Extracellular to intracellular K+ Shift, Decreased potassium intake, Increased GI Loss, and Increased urinary loss

question

Specimens for the determination of K+

answer

serum or plasma must avoid hemolysis.

question

Chloride

answer

Major anion of the extracellular fluid

question

Output of Cl-GI tract, skin, urine
occurs through three principle routes:

answer

GI tract, skin, urine

question

Chloride Excess

answer

Accumulation occurs when intake exceeds output because of some abnormality n homeostatic mechanism

question

Chloride Depletion

answer

Occurs when output exceeds intake

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