Electrolytes Flashcards
Anion
A negatively charge ion, i.e. one that would be attracted to the anode in electrolysis.
Cation
A positively charged ion, i.e, one that would be attracted to the cathode in electrolysis.
Anion Gap
A measurement of the difference- or gap-between the negatively charged and positively charged electrolytes.
Active Transport
The process of moving molecules across a cellular membrane through the use of cellular energy.
Passive Transport
A type of membrane transport that does not require energy to move substances across cell membranes.
Electrolyte
The ionized or ionizable constituents capable of carrying an electric charge.
Extracellular Fluid
Body fluid that is not contained within cells.
Intracellular Fluid
Body fluid that is contained within the cells and cytosol.
Osmolality
A measure of the number of dissolved particles in a fluid. (i.e. sodium, potassium, etc.)
Osmolarity
The number of particles of solute per liter of solution.
Osmolal Gap
The difference between measured serum osmolality and calculated serum osmolality.
Diabetes Insipidus
A disorder of salt and water metabolism barked by intense thirst and heavy urination.
Polydipsia
Excess thirst
Anion
Electrolytes with a negative charge; moves towards the anode.
Cation
Electrolytes with a positive charge; move towards the cathode.
Anion Gap
A measurement of the difference- or gap-between the negatively charged and positively charged electrolytes.
Active Transport
A mechanism that requires energy to move ions across cellular membranes.
Ex: Na/K Pump
Passive Transport (Diffusion)
The passive movement of ions (no energy consumed) across a membrane.
Dependent on the size and charge of ion being transported.
Osmolality
Physical property of a solution that is based on the concentration of solutes expressed as milliosmoles/kg of solvent (w/w).
Extracellular Fluid
Accounts for 1/3 of the total body water and can be subdivided into intravascular ECF (plasma), and the interstitial cell fluid which surrounds the cells in the tissue.
Osmosis
The spontaneous passage or diffusion of water or other solvents through a semipermeable membrane.
Movement of solvent from low to high solute concentration.
Osmosis
The spontaneous passage or diffusion of water or other solvents through a semipermeable membrane.
Movement of solvent from low to high solute concentration.
Osmotic Pressure
The amount of pressure required to exactly oppose osmosis into any solution across a semipermeable membrane separating it from pure water.
Proportional to the number of dissolved solute particles per unit volume.
Osmotic Pressure
The amount of pressure required to exactly oppose osmosis into any solution across a semipermeable membrane separating it from pure water.
Proportional to the number of dissolved solute particles per unit volume.
Oncotic Pressure
Osmotic pressure when there is a higher concentration of protein on the plasma side than the interstitial side of the cell membrane.
Hydrostatic Pressure
Blood Pressure
Homeostasis
Maintenance of a steady state in the body of a relative constant concentration of ions, pH, and osmotic pressure in the various body fluids.
Homeostasis
Maintenance of a steady state in the body of a relative constant concentration of ions, pH, and osmotic pressure in the various body fluids.
What is the body’s response to variation in plasma osmolality under the following condition:
Increased plasma osmolality
(1) Increased stimulation of arginine vasopressin hormone (AVP), increases retention of water in body
(2) increased sensation of thirst, increases intake in water
What is the body’s response to variation in plasma osmolality under the following condition:
Decreased plasma osmolality
Decreased stimulation of arginine vasopressin hormone (AVP) - lose water
What is the body’s response to variation in plasma osmolality under the following condition:
Decreased renal perfusion pressure
Increase in angiotensin II - increase aldosterone and retain sodium and vasoconstrict vessels
What are five factors affecting blood volume?
(1) Renin-angiotensin system
(2) Volume receptors independent of osmolality stimulate the release of AVP, which conserves water by renal absorption
(3) Atrial natriuretic peptide (ANP) - released from the myocardial atria in response to volume expansion; promotes sodium excretion in the kidney
(4) Glomerular filtration rate (GFR) - increases with volume expansion and decreases with volume depletion
(5) Increased sodium in urine or plasma
What type of specimen should be used for osmolality analysis?
Serum or Urine
Why can’t plasma be used for osmolality?
The possibility of introducing osmotically active substances to the specimen from the anticoagulant.
The sample should be free of particulate matter to obtain accurate results.
For direct test osmolality, what is being tested?
The properties of freezing point, boiling point, and vapor pressure.
For an increase in osmolality, what will the outcome of the tests be?
Decrease in freezing point temperature and vapor pressure, and an increase in the boiling point temperature.
What is the reference interval for osmolality for both serum and urine?
Serum: 275-295 mOm/kg
Urine: 300 - 900 mOsm/kg
Osmolal Gap
(Direct Osmolality) - (Indirect Osmolality)
What does it mean if the osmolal gap is high?
That some osmotically active substance (other than Na, glucose, or BUN) is present in the serum or urine, or proteins are present in higher amounts than normal.
Sodium
Most abundant cation in the ECF.
Function of Sodium
- Regulates water
- Can passively move/diffuse into the red cell
- ATP needed to pump Na out of the red cell/other tissue cells
Regulation of Sodium
Renal control, freely filtered by the glomerulus, majority actively reabsorbed by proximal convoluted tubule.
Reference interval of Sodium
135 - 145 mmol/L
Hyponatremia
Serum/plasma levels less than 135 mmol/L; below 130 mmol/L are critical values; below 120 mmol/L a medical emergency.
Hypernatremia
Serum/plama levels greater than 145 mml/L; above 160 mmol/L are critical values.
How is Sodium tested?
Ion selective electrodes.
Semipermeable membrane, with two electrodes:
(1) Internal reference electrode/constant potential
(2) Glass electrode (measuring electrode)
The difference in potential can be measured as activity and converted to concentration.
Sodium specimen requirement
Serum or heparin plasma.
Potassium
Major intracellular cation
Function of Potassium
Neuromuscular excitability, along with Mg, controls the rate and force of contractions of the heart.
Regulation of Potassium
Dietary - need about 50 - 150 mmol/day, aldosterone, active reabsorption in the proximal tubules, reciprocal relationship with H ion.
Reference interval of Potassium
Plasma, Males: 3.5 - 4.5 mmol/L;
Plasma, Females: 3.4 - 4.4 mmol/L
Serum: 3.5 - 5.1 mmol/L
Critical Values of Potassium
Less than 2.8 mmol/L
Greater than 6.2 mmol/L
Hypokalemia
A plasma K+ concentration below the lower limit of the reference range.
Can occur with GI or urinary loss of K+ or with increased cellular uptake of K+.
Hyperkalemia
A plasma K+ concentration above the upper limit of the reference range.
Common with patients with underlying disorders, such as renal insufficiency or diabetes mellitus.
How is Potassium tested?
Ion Selective Electrodes (ISE) - a valinomycin membrane is used to selectively bind K+ causing an impedance change that can be correlated to K+ concentration, where KCl is the inner electrolyte solution.
Atomic Absorption Spectroscopy - light absorbed is proportional to concentration of sodium and potassium. Not common in clinical laboratories.
What happens to Potassium with increased platelets?
Increased potassium in serum
What happens to Potassium with increased leukocytes?
Increased potassium in serum.
Chloride
Major cellular anion
Function of Chloride
Osmotic pressure, proper body hydration, electric neutrality balances cations and anions.
Regulation of Chloride
Dietary intake; kidney - excess is lost in urine.
Reference intervals of Chloride
Plasma, Serum: 98 - 107 mmol/L
Chloride Shift
CO2 generated by cellular metabolism within the tissue diffuses out into both the plasma and the red cell. In the red cell, CO2 forms carbonic acid, which splits into H+ and HCO3-. Deoxyhemoglobin buffers H+, whereas the HCO3- diffuses out into the plasma and Cl- diffuses into the red cell to maintain the electric balance of the cell.
Hyperchloremia
An electrolyte imbalance and is indicated by a high level of chloride in the blood.
Hypochloremia
An electrolyte imbalance and is indicated by a low level of chloride in the blood.
How is Chloride tested?
Ion Selective Electrode - AgCl electrode with silver sulfide sensing element.
Bromide from medications may interfere.
Sample needed for Chloride testing.
Serum or heparinized plasma.
Amperometric-moulometric titration
Chloride in solution is titrated with Ag ions which are formed at a constant rate by the passage of an electric current. As long as Cl ions are present the conc. of silver ions remains low. When Cl ions are gone, Ag ions goes up and this is detected by a silver electrode and an associated circuit automatically stops titration and timer
Bicarbonate
Second most abundant anion in the ECF. Makes up most of the total carbon dioxide of venous plasma.
Function of Bicarbonate
Plays a role in acid/base balance.
Regulation of Bicarbonate
Most of the bicarbonate in the kidneys is reabsorbed by the proximal tubules (85%); 15% by the distal tubules.
Reference interval of Arterial Bicarbonate
22 - 26 mmol/L,
total CO2 23 - 27 mmol/L
Reference interval of Venous Bicarbonate
24 - 28 mmol/L,
total CO2 25 - 29 mmol/L
How do you determine total CO2?
The sum of all forms of CO2 found in the blood (dissolved CO2, bicarbonate, carbonic acid)
Calculation method derived from pH and pCO2
Total CO2 = (pCO2 x 0.0306) + HCO3
When is total CO2 measured?
When CO2 from a sample diffuses through a semipermeable membrane into an electrolyte solution. A change of pH is measured.
Enzymatic methodology for bicarbonate testing
The specimen is alkalinized to convert all forms of CO2 to HCO3. HCO3 + phosphoenol pyruvate(PEP) yields oxaloacetate which + NADH + H in the presence of malate dehydrogenase yield malate + NAD+ which is measured at 340 nm. The decrease in 38 NADH is proportional to the total CO2 content.
Magnesium
Second most abundant intracellular ion, fourth most abundant cation in the body.
Function of Magnesium
Myocardial rhythm and contractility, essential cofactor in more than 300 enzymes; involved in cardiovascular, metabolic and neuromuscular disorders
Regulation of Magnesium
Small intestine may absorb 20% to 65% of the dietary Mg2+, depending on need and uptake. Overall regulation is controlled largely by the kidney, which can reabsorb Mg2+ in deficiency states or readily excrete excess Mg2+ in overload states
Reference interval of Magnesium
Serum, colorimetric: 1.26 - 2.10 mg/dL = 0.63 - 1.0 mmol/L
Magnesium testing methodology
Colorimetric Methods:
(1) Calmagite: Reddish-violet complex read at 532 nm
(2) Formazan dye: Colorex complex read at 600 nm
(3) Methylthymol blue: A colored complex
Calcium
Cation found in plasma as ionized Ca, or 45- 50% bound to protein, some bound to citrate
Function of Calcium
Bone and teeth formation, membrane permeability, neuromuscular excitability- regulates primary sensory neurons, transmission of nerve impulses, blood coagulation, activities for enzymes including activation
Regulation of Calcium
Three hormones regulate Ca2+, PTH, vitamin D and calcitonin
Reference Interval of Calcium
8.6 - 10.0 mg/dL
Regulation of Calcium
PTH secretion in blood is stimulated by a decrease of ionized Ca+2, and conversely, PTH secretion is stopped by an increase in ionized Ca2+.
PTH exerts three major effects on both bone and kidney. In the bone, PTH
activates a process known as bone resorption, in which activated osteoclasts break down bone and subsequently release Ca+2 into the ECF.
In the kidneys, PTH conserves Ca+2 by increasing tubular reabsorption of Ca+2 ions. PTH stimulates renal production of active Vit D
Calcium Testing Methodology
Ionized free calcium uses ISE for the measurement.
Preferred specimen for Calcium testing
Serum or lithium heparin plasma.
Phosphate
An anion found in the human body
Function of Phosphate
Phosphate compounds participate in many of the most important biochemical processes. E.g. myocardial rhythm and contractility
Phosphate Regulation
May be absorbed in the intestine from dietary sources.
Phosphate Reference Intervals
0.78-1.42 mmol/L = 2.4 - 4.4 mg/dL
Lactate
Byproduct of an emergency mechanism that produces a small amount of ATP when oxygen delivery is severely diminished.
Lactate Reference Interval
0.5 - 2.2 mmol/L
Lactate Specimen Handling
Special care should be practiced when collecting and handling specimens for lactate analysis: no tourniquet and put on ice slush once drawn.
Draw in NaFl tube, use plasma, or can be done point of care, whole blood.
Formula to determine Anion Gap
(Na + K) - (Cl + HCO3)
Formula to determine Anion Gap without Potassium
Na - (Cl + HCO3)
Causes of increased anion gap
- Salicylate intoxication
- Lactic acidosis
- Unmeasured anions
- Methanol
- Polyethylene glycol
- Ethanol
- Diabetic ketoacidosis
- Uremia
- Plasma proteins
- Decrease in unmeasured cations (Ca or Mg)
