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Physiology > Lecture 5: Electrolytes > Flashcards

Lecture 5: Electrolytes Flashcards

1
Q

Total body water distribution

A

Total body weight: 40% dry, 60% water

Total body water: 66% ICF, 33% ECF

Extracellular water: 20% plasma, 80% interstitial

See figure

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2
Q

What % of total body weight are plasma volume and blood volume?

A

Plasma volume: 4% of total body weight

Blood volume (40% Hit): 7% total body weight

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3
Q

What % of total body weight is made of total body water?

A

45 - 75%

Variability depends on sex, % body fat, % skeletal muscle, age

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4
Q

What % body weight is represented by total body water for males vs females

A

Males: 60%

Females: 50%

Females have increased fat, which decreases % water

Males have increased muscle, which increases % water

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5
Q

What does age do to the % body weight of total body water

A

Increasing age decreases % body weight

Newborn: 75%

1 year: 65%

adult 50 - 60%

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6
Q

Relationship of ECF (plasma, interstitial) and ICF

A

See figure

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7
Q

What other system drains into the interstitial?

A

Lymphatic fluid

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8
Q

Relative ion amounts in extracellular vs intracellular fluid

A

High in extracellular: Na, Ca, Cl, HCO,

High in intracellular: K, Mg, HPO4, Protein

See figure

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9
Q

What are the extracellular and intracellular concentrations of Na

A

Extracellular: 140 (plasma), 146 (interstitial)

Intracellular: 12

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10
Q

What are the extracellular and intracellular concentrations of K

A

Extracellular: 4 (plasma), 4 (interstitial)

Intracellular: (150)

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11
Q

What are the extracellular and intracellular concentrations of Cl

A

Extracellular: 103 (plasma), 104 (interstitial)

Intracellular: 3

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12
Q

What happens once gradients are established in the ECF and ICF?

A

little movement of ions between ECF to ICF

water moves easily across plasma membranes based on osmotic forces

if sodium is added to the ECF – amount of Na in the ECF increases; amount of Na in ICF is unchanged

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13
Q

Distribution of anions and cations in the ECF and ICF

A

See figure

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14
Q

Control of ICF and ECF

A

ICF is tightly controlled

ECF is less tightly controlled

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15
Q

What movement does the capillary wall allow?

A

Fluid and electrolytes

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16
Q

Movement across cell membrane

A

Plasma membrane contains channels and pumps which control the movement of electrolytes

Water moves easily across via osmotic forces

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17
Q

What controls movement between plasma and interstitial fluid?

A

Starling forces

See figure

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18
Q

What forces move fluid out of the capillaries?

A

PC = hydrostatic pressure in capillary (changes along capillary, 37 to 17mm Hg)

pi = oncotic (colloid) pressure in interstitium (~0-1 mm Hg)

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19
Q

What happens to movement between plasma and interstitial when venous pressure increases?

A

Increased PC may produce edema since fluid can’t return.

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20
Q

What focus move fluid into capillaries?

A

Pi = hydrostatic pressure in interstitium (~1-2 mm Hg)

pC = oncotic (colloid) pressure in capillary (25 mm Hg)

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21
Q

What happens if the lymphatic system doesn’t drain the interstitial and return fluid to circulation?

A

Edema

The arterial ends of the capillaries have sphincters to control pressure

The venous end of the capillaries do not have these sphincters

See figure

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22
Q

What determines fluid movement between plasma and interstitial space?

A

Hydrostatic pressure

changes in osmolality play a minor role (but still important)

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23
Q

What does an increase in arterial pressure (BP) do to the PC?

A

does not increase PC (at least directly) since pre-capillary sphincters control the pressure in the capillaries

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24
Q

What does an increase in venous return to the heart do to the PC?

A

if the heart is unable to pump blood forward, the pressure backs up into veins

the increased venous pressure increases PC, leading to edema

See figure

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25
Q

What happens if lymphatic system is not working properly?

A

Fluid accumulates in the lymphnodes

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26
Q

How is the electrochemical gradient regulated?

A

The Na/K ATPase establishes/maintains the electrochemical gradient

Ion channels regulate ion movement across membranes

This allows alteration of membrane potential – e.g. action potential

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27
Q

Water movement between ICF and ECF

A

Water moves easily/freely between the two compartments (ICF:ECF)

Water movement is driven by differences in osmolality

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28
Q

What are the osmolalities of the ICF and ECF at steady state>

A

They are the same

this is due to the bidirectional movement of H2O, not solute movement

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29
Q

What is the major osmotically active cation outside the cell? Can its concentration change?

A

Sodium

Concentration can change a fair amount (diet, dehydration)

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30
Q

What is the major osmotically active cation inside the cell? Can its concentration change?

A

Potassium

its concentration should not change very much in or out of the cell

otherwise, arrhythmia/death can occur- especially with a change in extracellular fluid

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31
Q

What are the main consequences OF changes in sodium and potassium?

A

Sodium produce osmolality changes and cause water movement between ICF and ECF

Potassium produce changes in resting membrane potential (RMP) and cellular excitability

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32
Q

What is osmolality?

A

instrument measurement of solutes in a solution

reported as
mOsmol/Kg of solvent

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33
Q

What is osmolarity?

A

calculated measurement of solutes in a solution and reported as mOsmol/litre of solvent

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34
Q

What is osmotic pressure?

A

the pressure needed to prevent the movement of water across a semipermeable membrane

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35
Q

What is tonicity?

A

osmotic pressure gradient of two solutions separated by a semipermeable membrane, usually in reference to plasma.

36
Q

Where does osmosis occur?

A

between two separated compartments if the membrane allows water but not solute movement (e.g. ECF and ICF)

37
Q

What produces osmotic pressure?

A

Difference in osmolality on two sides of membrane

since solutes can’t cross the membrane but water can, the hypertonic side appears to “pull” water out of the hypotonic side.

38
Q

Is it better to drown in fresh water or salt water?

A

Freshwater (hypotonic) drowning: cells will burst

Seawater (hypertonic) drowning: cells shrink

Shrunken cells can still be restored

So, it’s better to drown in seawater

39
Q

What solutes play a major role in plasma osmolality?

A

Sodium and it’s associated anions

40
Q

Formula to calculate osmolality in mOsm/L

A

calculated osmolality (CO) = (2 x [Na]) + [glucose] + blood urea nitrogen (BUN)

in a healthy person, the calculated osmolality is predictably about 10 mOsm/L less than the actual measured osmolality

41
Q

PNa (and hence osmolality) and water movement

A

See figure

42
Q

Why is sodium important in determining total body water?

A

changes in plasma sodium concentration change plasma osmolality

when plasma osmolality changes:

water distribution changes (intracellular and extracellular) - acute and small correction normally

43
Q

What hormone levels change for water and sodium regulation?

A

vasopressin and aldosterone

required for chronic correction

44
Q

Vasopressin (site of release, effect, when would we want it)

A

released from posterior pituitary

increases water reabsorption in collecting duct of kidney

Want this in hypertonic conditions

45
Q

Aldosterone(site of release, effect, when would we want it)

A

released from adrenal medulla

increases sodium reabsorption in distal tubule of kidney

would want this in hypotonic conditions

46
Q

What happens if you ingest large volumes of water?

A

could be due to excessive water reabsorption - SIADH)

water absorbed from gut into the plasma
dilution of PNa

hyponatremia and decreased osmolality ê
osmotic gradient now favors movement of fluid into cells

water moves (is drawn) into cells to balance osmotic gradient

cell size increases
normally not a problem (except in the brain)

47
Q

What happens when you ingest or infuse sodium and little/no water

A

INCREASED NA IN PLASMA (increases vascular volume and TBW)

If you ingest or infuse sodium and little/no water
(increases total body sodium but only in ECF)

plasma sodium concentration rises, increasing plasma osmolality (osmol receptors in hypothalamus - increases vasopressin release)

water moves (is pulled) out of cells to balance osmolality

plasma osmolality still slightly elevated when balanced

vasopressin retains water in the kidney and helps dilute plasma back to normal osmolality

Now have increased extracellular (interstitial and plasma) volume (Na and H20). Cells returned to previous volume (and osmolality)

48
Q

What happens when you lose sodium or have not enough loss of water?

A

DECREASED VASCULAR VOLUME AND TBW

plasma sodium concentration drops, decreasing plasma osmolality (this turns off vasopressin but increases aldosterone release)

water moves (is pulled) into cells to balance osmotically

fluid shifts from ECF to ICF: decreases plasma volume

plasma osmolality remains slightly decreased aldosterone retains sodium in the kidney helps correct low sodium

now have decreased extracellular (interstitial and plasma) volume (sodium and water)

49
Q

Why do we calculate the plasma osmolality (CO) when it can be measured?

A

This equation shows the major importance of Na.

If the measured osmolality (MO)&raquo_space;> calculated osmolality (CO), this indicates that there is a foreign substance in the blood

50
Q

Osmolar gap calcularion

A

OG = MO - CO

Normally about 10 mOsmol/L

51
Q

What does MO measure?

A

Measures the osmolar effects of all substances in the blood including sodium, glucose, BUN and any foreign substances if osmotically active

52
Q

What does CO measure?

A

Only measures osmolar effects of sodium, glucose and BUN

53
Q

What does a high osmolar gap indicate?

A

poisoning with alcoholic beverages, ethanol, wood alcohol (methanol), rubbing alcohol or antifreeze

(osmotically active in blood and blood levels can be high)

54
Q

Where is the OG most helpful?

A

narrowing down causes of metabolic acidosis (later)

55
Q

What is the electrical charge of plasma?

A

Electroneutral (cations = anions)

56
Q

What are the normal major cations and anions in blood?

A

cations: Na and K (less so K)
anions: HCO3 and Cl

57
Q

How to estimate the normal calculated anion gap

A

Na+ - (HCO3- + Cl-)

Eq’n says NaHCO3 and NaCl account for most cation/anion associations

will also account for Na associated with other anions (small in number)

58
Q

What happens if anion gap increases when estimated?

A

Something other than HCO3, Cl and the small number of unmeasured anions is also associated with Na

The level of sodium doesn’t change but the anions it is associated with does

Tells you there is more of an unmeasured anion present that is linked to sodium

59
Q

Normal plasma sodium concentration

A

135-145 mmol/litre

60
Q

What does low sodium concentration in the plasma tell you about the movement of water between the ECF and ICF?

A

Water moves into the ICF

61
Q

What does low sodium concentration in the plasma tell you about the relation of sodium to water in the ECF?

A

More water

62
Q

What does low sodium concentration in the plasma tell you about the plasma volume (low, high or normal)?

A

Requires more info

63
Q

What does a high sodium concentration in the plasma tell you about the movement of water between the ECF and ICF?

A

Moves into ECF

64
Q

What does a high sodium concentration in the plasma tell you about the relation of sodium to water in the ECF?

A

More sodium

65
Q

What does a high sodium concentration in the plasma tell you about the plasma volume (low, high or normal)?

A

Requires more info

66
Q

What is hyponatremia?

A

(only tells you more water than sodium in ECF)

low sodium concentration in plasma

decreased plasma osmolality

increased water in relation to sodium

water would move from plasma to enter cells

can be problematic in brain, producing cerebral edema

67
Q

What is hypernatremia?

A

(only tells you more sodium than water in ECF)

increased sodium concentration in the plasma

increased plasma osmolality

decreased water in relation to sodium

water would move from cells to plasma

may be useful, to treat cerebral edema caused by head injury - may be harmful, decreases brain volume

68
Q

Why is plasma volume important?

A

allows the heart and circulation to function properly!

If plasma volume is too high or low - cardiovascular problems may occur which may be life threatening.

69
Q

What is the total body water or plasma volume of a patient with a chronic plasma sodium concentration of 125 mmol/L

Is plasma volume high, normal or low?

A

ANSWER – we don’t know

Additional information required: volume status of patient to go along with the PNa

70
Q

What is hypovolemia? How is it assessed?

A

insufficient vascular volume

history (vomiting, diarrhea, fluids,

physical (BP, HR, skin turgor, mucous membranes, etc)

urine output (volume, colour)

71
Q

What is hypervolemia? How is it assessed?

A

excessive vascular volume

increased weight

indications heart can not adequately deal with the increased volume (backs up into venous system, edema in lower extremities to start

possible ascites (fluid in abdomen), pulmonary edema

72
Q

How to identify problem using PNa and volume status

A

See figure

73
Q

What is plasma potassium used for?

A

important in determining intracellular osmolality

cells tightly regulate their internal milieu (K changes little)

74
Q

Why are changes occurring in extracellular potassium relative to intracellular potassium critical?

A

These can produce major effects on the resting membrane potential.

this can cause problems in electrically conducting tissues (nerves, heart)

75
Q

Intracellular and serum concentration of K+

A

Intracellular: 140-150 mmol/L

serum: 3.5-5 mmol/L

even small change in serum levels can be life-threatening

76
Q

What can be used to evaluate changes in heart function?

A

EKGs

if changes are chronic and gradual, some patients may be asymptomatic at 6.5 mmol/L whereas others might not survive this as an acute change

77
Q

How does the body respond to changes in plasma potassium?

A

acutely: drive potassium into or out of cells (hide or release potassium?)
chronically: the kidney becomes important (distal nephron sodium delivery , renal actions of aldosterone)

78
Q

What alters the RMP? What alters the threshold?

A

plasma potassium alters the resting membrane level

plasma calcium alters the threshold level

do not want the RMP getting close to the threshold potential

79
Q

How to treat low plasma potassium (hypokalemia)

A

can administer K slowly (diet, intravenously)

must be cautious against producing hyperkalemia

80
Q

How to treat high plasma potassium (hyperkalemia)

A

can drive K into cells (short term solution) - in emergencies give insulin, β-adrenergic receptor stimulation, alkalosis (H leaves the cell in exchange for K entering)

Aldosterone (kidney, long term) - sodium reabsorption and potassium secretion (loss)

calcium to depolarize the threshold potential (i.e. - more positive potential)

81
Q

How do IV solutions work?

A

Fluids and electrolytes are administered to correct imbalances in electrolytes and to correct plasma volume, ECF volume and/or total ECF and ICF volume.

The solvent (water) will follow the solute (glucose or saline)

82
Q

5% dextrose in water (IV solution) distribution

A

D5W

will distribute through all fluid compartments. Less than 10% will remain in the plasma – it distributes through all body water

83
Q

Normal saline (IV solution) distribution

A

distributes in extracellular fluid with only 20% remaining in plasma

84
Q

Dextran, mannitol, albumin IV solution distribution

A

larger molecules that remain in the vascular space

will expand the plasma/blood volume

85
Q

What happens when dextrose in water is given as an IV

A

glucose is useful, but rapidly metabolized to CO2 + H2O

so essentially only giving water (easily distributes)

volume distributed into intracellular as well as extracellular (distributes in total body water)

D5W, D10W (5 or 10% dextrose in water)

Volume replacement and caloric supplement (no electrolytes)

See figure

86
Q

What happens when saline solution is given as an IV

A

come in a variety of concentrations: hypotonic (0.2%), isotonic (0.9%), and hypertonic (5%).

provides sodium, chloride, water

sodium maintains osmolality

water helps to maintain blood volume and organ perfusion

increases interstitial volume

87
Q

What happens when dextran solution is given as an IV

A

Dextran: a long chain polysaccharide (a long sugar)

solutions are confined (large molecule) to the vascular compartment- preferentially expand this portion of the ECF.

albumin (protein) solutions are much the same

Physiology (19 decks)

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