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Chemistry 2 > electrolytes 1 > Flashcards

electrolytes 1 Flashcards

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1
Q

references ranges for osmolality

  • serum
  • osmolar gap
  • critical values
A

serum : 275-295 mOsm/kg
*urine has a wider range than serum
osmolar gap : 5-10 mOsm/kg
critical serum values : <250 & > 325 mOsm/kg

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2
Q

what is the ultimate regulator of water in the body

A

Kidneys

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3
Q

hormones and water balance

A

Arginine Vasopressin Hormone (AVP )

  • antidiuretic hormone(ADH)
  • increases water reabsorption
  • secreted by the hypothalamus

Aldosterone

  • increases Na+ reabsorption
  • produced by adrenal cortex
  • increased aldosterone= more Na+( and Cl-) reabsorbed in exchange for H= (or K+) secretion into urine
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4
Q

body weight % of water

amount that is intracellular & extracellular

A

40-75% water

2/3 is intracellular
-40-50%

1/3 is extracellular

  • intravascular (plasma) 5%
  • interstitial (lymph & tissue) 15%
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5
Q

anions and anode

cations and cathode

A

anions (-) move toward the anode (+)
cations (+) move towards the cathode (-)

electrolytes are substances that split into ions

total anions =total cations
- an increase in one anion means another anion must decrease or a cation must increase to keep balance

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6
Q

main anion and cation of intracellular fluid & extracellular fluid

A

ICF

  • main cation is K+
  • main anion is HPO4(2-) aka phosphate

ECF

  • main cation is Na+
  • main anion is Cl-
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7
Q

what should you do if you have a high K+ result on a patient

A

first check for hemolysis ( hemolysis falsely increase K+)
then rerun
then report

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8
Q

what has osmolality replaced for testing

A

it has replaced specific gravity as the test to assess renal concentration

SG includes number & size of molecules

osmolality is a measure of concentration based only on the number of small molecules present in solution ( not weight or size )

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9
Q

Colligative properties

A

solution properties related to the number if molecules ( particles present in the solvent

increasing the number of particles in a solution will

  • lower freezing point
  • higher boiling point
  • increased osmotic pressure
  • lower vapor pressure

if 1 Osmol of any solute is added to 1 kg of water the freezing point is decreased by 1.86 degrees Celsius

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10
Q

Na+ accounts fro what % of osmotic activity in plasma

A

• The concentration of Na+ in plasma is affected by:

  • The regulation of osmolality
  • The regulation of blood volume

• Osmoreceptors in the hypothalamus respond to small changes in
osmolality.
- An increase in osmolality causes an increase in AVP concentration.
- A decrease in osmolality shuts off AVP production.

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11
Q

water deficit

A
  • Thirst is important in preventing water deficit.
  • Deficit of H2O will increase plasma osmolality.
  • AVP and thirst will be activated
  • AVP will cause H2O to be reabsorbed

• Thirst is the major defense against hyperosmolality and hypernatremia
• Hyperosmolality and hypernatremia is a concern for:
- Infants
- Unconscious patients
- Older patients
- Those with diminished mental status

• For these patients, dehydration is a concern

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12
Q

water excess

A

• Excess intake of H2O (polydipsia) will lower plasma osmolality.
• AVP and thirst will be suppressed
• H2O will not be reabsorbed
• Large volume of dilute urine excreted (10 - 20 L)
• Hypoosmolality and hyponatremia usually only occur if there is an
impairment with the renal excretion of water

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13
Q

diabetes insipidus

A

• No AVP production or no ability to respond to circulating AVP
• Excessive thirst
• Increased urine output (up to 10 L/day)
• Water intake = water output
• Plasma osmolality remains normal
• Because thirst response is normal in these patients, dehydration is
prevented.

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14
Q

Regulation of blood volume - decreased blood volume or pressure (hypovolemia)

A

Renin converts angiotensinogen to angiotensin l
angiotensisn converting enzyme ( ACE) converts Angiotensin l to angiotensin ll
angiotensin ll causes vasoconstriction
- blood pressure is increased
Aldosterone is excreted which increases retention of Na+ ( and the H2O that accompanies it )

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15
Q

Regulation of blood volume - increased blood volume/ pressure ( hypervolemia )

A
  • Atrial natriuretic peptide (ANP) is released from myocardial atria
  • Promotes Na+ excretion in kidney
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16
Q

specimens for osmolality

A

• Measured on serum or urine (not plasma)

  • Plasma may have osmotically active particles from the anticoagulant
  • Sample must be free of particles or centrifuged prior to testing

• Clinical unit of measure is the milliosmole (mOsm/kg)

17
Q

common methods for analysis of osmolality

A
  • Freezing point depression
  • Vapor Pressure decrease

-Freezing point osmometers use sodium chloride as reference
solutions (calibrators).

18
Q

Osmolality Measurement: Freezing Point Depression Osmometer

A
  • Sample is supercooled to -7 degrees C
  • Supercooling - cooling below the freezing point but remaining in a liquid state

• Mechanical agitation ‘seeds’ crystal formation
• As crystals form, the heat of fusion is released and the solution warms to its
freezing temperature and freezes

  • Probe measures freezing point
  • Final reading is taken reflecting the freezing point of the solution

• The more particles present in a sample, the more the freezing point is depressed
(lowered)

19
Q

Calculated Osmolality

A
  • Based on the major contributors to serum osmolality: glucose, urea and sodium
  • Sodium is always with chloride (therefore 2 ions upon dissociation)

1.86*(Na+ mmol/L) + glucose (mmol/L) + urea (mmol/L)

20
Q

Oamolal Gap

A

Difference between the measured and the calculated osmolality

• An increased osmolal gap may indicate the presence of other
osmotically active substances:
• Ethanol, methanol, ethylene glycol, isopropanol, lactate or β-hydroxybutyrate

- ex. an increase in lactate may occur due to increased anaerobic metabolism 
of glucose (pyruvate → lactate) during an AMI
  • an increase in β-hydroxybutyrate ( a ketone body ) is increased if someone is diabetic

• The osmolal gap should be 5 - 10 mOsm/kg

21
Q

Electrolyte functions

  • maintains osmotic pressure & water distribution
  • maintains pH
  • regulates the function of heart & other muscles
  • oxidation- reduction rxns
A
  • Maintain osmotic pressure and water distribution (Na+)
  • Maintain pH (HCO3-/H+)
  • Regulate the function of heart and other muscles (K+, Ca++)
  • Involved in oxidation-reduction reactions (H+)

• Act as cofactors for enzymes

22
Q

Ion-Selective Electrode Potentiometry - Key Words

oxidation , reduction , anode, cathode, electrochemical cell

A

Oxidation - loss of electrons at the anode

Reduction - gain of electrons at the cathode

Anode - positive electrode; where oxidation takes place

Cathode - negative electrode; where reduction takes place

Electrochemical cell - combination of 2 half cells (oxidation and reduction),
connected by a salt bridge

23
Q

potentiometry & principle

A 
measures voltage (mV) generated by an electrochemical cell at 
zero current

Difference between potential from the reference electrode and the indicator (ISE) electrode

24
Q

electrochemical cell

A

• Electrochemical cell - 2 half cells or electrodes connected by a salt bridge

  • Indicator (ISE) Electrode - detects the ion of interest
  • Reference Electrode - provides constant potential

Note: ISE’s used in instruments have all the components (indicator electrode,
reference electrode and salt bridge) in one unit.

25
Q

indicator electrode

A

• Measuring electrode constructed to detect a specific ion of interest
• Generates electrical potential when placed in a solution containing
the ion to be measured.
• The potential generated is proportional to the concentration of the ion
(activity)

26
Q

reference electrode

A
  • Surrounded by a solution of constant composition
  • At constant pH; generates constant potential; compensates for changes in temp., electrical noise, age of electrodes, etc.
  • Common reference electrodes:
  • Silver/ silver chloride (Ag/AgCl)
  • Calomel (mercury/ mercury chloride) Hg/HgCl
27
Q

Nernst Equation

A

𝐸= (𝐸𝑜+2.39𝑅𝑇 / 𝑛𝐹 ) log𝑎

in brackets is the constant

slope = 2.3 RF/ nF

reduced equation = E~log a
i.e. measuring potential (mV) ~ activity (concentration) of the ion

28
Q

sloping of an electrode ( calibrating using 2 standards )

A

when conc & potential are plotted against each other on a semi log paper
- straight line

For a monovalent ion (eg. K+) Calibration Standards with tenfold difference have
voltage difference of 59.1mV

When the sample is analyzed, the mV reading is used to extrapolate the
concentration of ion from the slope

29
Q

Ion-Selective Electrodes selectivity

A
  • ISEs are selective but not specific
  • Other interfering ions are also measured to a slight degree

• Each ion has a selectivity factor to determine the amount of interference it
will cause

• Electrodes are designed to have the lowest possible selectivity factors for
interfering ions.

30
Q

classes of electrodes

A
  • Solid material (eg. Glass)• Specific types of glass used (eg. H+, Na+)
  • Can be modified using a gas-permeable membrane (eg. CO2)
  • Liquid (Ion-exchange)• Binds with ion being measured (eg. K⁺)
  • Solid state• Insoluble inorganic salts in a membrane; potential due to the ion exchange process. (eg. Cl⁻)
  • Enzyme• Enzyme bound to surface; reacts with a non-ion to produce ionic species which can then be measured (urea/urease = NH₄+)

Chemistry 2 (30 decks)

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