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Medical Physiology > Electrolytes > Flashcards

Electrolytes Flashcards

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USMLE® Step 1 flashcards
1
Q

How much of total body weight (blood volume) is plasma?

A

4%

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2
Q

What is the range of total body water in % of weight? what causes the variance?

A

45-75%

dependable on sex, body fat, skeletal muscle, and age

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3
Q

what is the typical body water for males and females? (%wt)

A

male - 60%

femae - 50%

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4
Q

what is the %wt body water for a newborn, 1 year old, and adult?

A

nb - 75%
1yo - 65%
adult - 50%

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5
Q

where is the capillary membrane and what is its function?

A

between plasma and interstitial fluid

allows easy movement of electrolytes and water

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6
Q

where is the plasma (cell) membrane and what is its function?

A

located between interstitial fluid and intracellular fluid

limits movement of electrolytes through tightly regulated pumps/channels but allows free movement of water

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7
Q

What is the Na concentration in the plasma, interstitial, and intracellular? Also state for K, Ca, Cl, and HCO

A

Order from plasma to interstitial to intracellular:
Na: 140, 146, 12
K: 4, 5, 150 (only one higher intracellularly)
Ca: 5, 1, 10^-7
Cl: 103, 104, 3
HCO: 24, 27, 10

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8
Q

what occurs once ion gradients are established?

A

little ion movement between ECF to ICF
water moves easily across membranes based on osmotic forces
Na added to ECF - does not change amount in ICF, only ECF

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9
Q

What %body wt is intracellular fluid? extracellular?

A

intra - 40%

extra - 20%

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10
Q

what is ICF?

A

volume within cells that is very tightly controlled

most ICF located in skeletal muscle

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11
Q

what is ECF?

A

volume not within cells that isn’t as tightly controlled

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12
Q

What causes water and solute movement between plasma and interstitium?

A

starling forces

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13
Q

What is Pc?

A

hydrostatic pressure in capillary that increases with incr. venous pressure (leads to edema)

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14
Q

what is pii?

A

oncotic (colloid) pressure in interstitium

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15
Q

what is Pi?

A

hydrostatic pressure in interstitium

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16
Q

what is pic?

A

oncotic pressure of plasma early in capillary

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17
Q 
what are the relative pressure measurements for the following:
Pc
pii
Pi
pic
A 
Pc = 37-20mmHg
pii = 0mmHg
Pi = 1mmHg
pic = 25mmHg
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18
Q

where do preload and afterload occur?

A

after - in artery after left ventricle (arterial resistance)

pre - in veins before right atrium (venous return)

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19
Q

where do preload and afterload occur?

A

after - in artery after left ventricle (arterial resistance)

pre - in veins before right atrium (venous return)

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20
Q

what is hypertension in terms of preload and afterload?

A

increase in afterload

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21
Q

what is the difference between left sided and right sided heart failure?

A

left: blood backs up in lungs (drowning feeling - could be life threatening)
right: blood backs up in periphery (edema)

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22
Q

what on the cell maintains ICF solute/electrolyte levels?

A

Na/K ATPase

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23
Q

what drives water movement?

A

difference in osmolality

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24
Q

What is the major osmotically active cation outside the cell?

A

Na

25
Q

what is the major osmotically acitve cation inside the cell?

A

K

26
Q

what allows movement of fluid between plasma and interstitial space?

A

changes in pic and Pc move fluids and electrolytes

27
Q

what allows movement between plasma and intracellular fluid?

A

sodium (osmolality changes and water movement)

K (resting membrane potential changes)

28
Q

what is K responsible for?

A

determining intracellular osmolality

29
Q

what could occur if there is a change in extracellular K relative to intracellular K?

A

major effects on resting membrane potential which could cause electrical conductance issues

30
Q

how does the body respond to changes in potassium? (acute and chronically)

A

acute - drive potassium in or out of cells

chronic - distal nephron Na delivery/renal actions of aldosterone

31
Q

how do you treat hypokalemia?

A

slowly administer K (diet or IV)

32
Q

how do you treat hyperkalemia? (short term and long term)

A

short term: stimulate beta-adrenergic receptor, cause alkalosis (H leaves, K enters), insulin in emergencies, and Ca (depolarize threshold potential)
long term: aldosterone (K secretion)

33
Q

how do you treat hyperkalemia? (short term and long term)

A

short term: stimulate beta-adrenergic receptor, cause alkalosis (H leaves, K enters), insulin in emergencies, and Ca (depolarize threshold potential)
long term: aldosterone (K secretion)

34
Q

what is osmolality?

A

instrument measurement of solutes in a solution reported as mOsmol/Kg of solvent

35
Q

what is osmotic pressure?

A

a pressure that needs to be applied to a solution to prevent movement of water across semipermeable membrane

36
Q

what is tonicity?

A

osmotic pressure gradient of two solutions separated by a semipermeable membrane which must be selective in blocking movement of solutes

37
Q

what is tonicity?

A

osmotic pressure gradient of two solutions separated by a semipermeable membrane which must be selective in blocking movement of solutes

38
Q

what occurs when cell is put in the following solutions?
isotonic
hypotonic
hypertonic

A

iso - nothing
hypo - cell swells
hyper - cell shrinks

39
Q

what is the equation to calculate osmolality?

A

(2 x [Na]) + [glc] + [BUN]

BUN = blood urea nitrogen

40
Q

what is a normal range of calculated osmolality? what is its accuracy compared to real measured osmolality?

A

280-300mOsm/L

within 10mOsm/L of measured values

41
Q

what happens in the body when you ingest a large amount of water?

A

1) water absorbed from gut into plasma (dilution of Pna and decr. osmolality)
2) osmotic gradient now favours fluid movement into cells
3) water moves into cell to balance osmotic gradient
4) cell size increases (hypotonic result)

42
Q

when is cell size increasing an issue? what is usually associated with it?

A

brain

low Pna associated with brain cell swelling

43
Q

what is hypervolemia? hypovolemia?

A

hyper - too much fluid

hypo - not enough fluid

44
Q

why is Na important in determining total body water?

A

changes in plasma [sodium] changes plasma osmolality, which changes water distribution and hormone levels (vasopressin and aldosterone)

45
Q

what happens in the body when you ingest a large amount of water? (4steps)

A

1) water absorbed from gut into plasma (dilution of Pna and decr. osmolality)
2) osmotic gradient now favours fluid movement into cells
3) water moves into cell to balance osmotic gradient
4) cell size increases (hypotonic result)

46
Q

why is Na important in determining total body water?

A

changes in plasma [sodium] changes plasma osmolality, which changes water distribution and hormone levels (vasopressin and aldosterone)

47
Q

what does vasopressin do?

A

released from post pit and increases water reabsorption in collecting duct of kidney?

48
Q

what does aldosterone do?

A

released from adrenal medulla and increases sodium reabsorption in distal tubule of kidney

49
Q

what happens when there is loss of Na? (4steps)

A

1) plasma [Na] drops, decreasing plasma osmolality (turn vasopressin off, incr. aldosterone release)
2) water moves into cells to balance osmolality
3) fluid shifts from ECF to ICF, decreasing plasma volume
4) plasma osmolality is slightly decreased (aldosterone retains sodium)

50
Q

What is Pc?

A

hydrostatic pressure in capillary that increases with incr. venous pressure (leads to edema)
determines fluid and electrolyte movement within ECF

51
Q

what is hypervolemia? hypovolemia? what does this reflect?

A

hyper - too much fluid (too much Na)

hypo - not enough fluid (too little Na)

52
Q

what happens when there is loss of Na? (4steps)

A

1) plasma [Na] drops, decreasing plasma osmolality (turn vasopressin off, incr. aldosterone release)
2) water moves into cells to balance osmolality
3) fluid shifts from ECF to ICF, decreasing plasma volume
4) plasma osmolality is slightly decreased (aldosterone retains sodium)

53
Q

what happens when there is an increase in Na? (4steps)

A

1) plasma [Na] rises, increasing plasma osmolality (vasopressin release)
2) water moves out of cells to balance
3) plasma osmolality still slightly elevated when balanced
4) vasopressin retains water in kidneys

54
Q

why calc osmolality if you can measure it?

A

shows importance of Na
if measured osmolality is greater than calc osmolality, that can indicate that something is increasing osmolality other than sodium, glc, or BUN (indicates foreign substance in blood)

55
Q

what is the osmolal gap? what is the usual value?

A

the difference between measured and calc values and can detect presence of unknown substance
usually 10mOsmol/L

56
Q

what does a high osmolal gap indicate?

A

poisoning with alcohol or antifreeze

57
Q

what does a high osmolal gap indicate?

A

poisoning with alcohol or antifreeze

58
Q

what is electroneutral?

A

cations = anions

Medical Physiology (15 decks)

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