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M2 Renal/FEK > 2. Sodium and Water I > Flashcards

2. Sodium and Water I Flashcards

1
Q

how should we think of volume regulation and osmoregulation?

A

they are separate: linked by ADH, but separate processes

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2
Q

what is the difference between osmolarity and osmolality?

A

for the purposes of this course, they can be used interchangeably. they refer to concentration of solute per L or Kg of solvent

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3
Q

what formula describes the movement of water via osmotic pressure?

A 
osmotic pressure = nCRT
n = dissociable particles per molecule
C = concentration of solute in solvent
R = constant (0.082)
T = temp in K
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4
Q

what are some common isotonic fluids?

A

normal saline, Ringer’s Lactate

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5
Q

what are some common hypotonic fluids?

A

1/2 normal saline, 5% dextrose in water (rapidly metabolized to 0 mosm/L)

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6
Q

what is a common hypertonic fluid?

A

3% NaCl

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7
Q

hypo/hypernatremia is a problem of what?

A

water

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8
Q

hypo/hypervolemia is a problem of what?

A

sodium

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9
Q

sodium determines volume where?

A

extracellular volume

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10
Q

usual concentration of sodium in extracellular space?

A

140 mmol/L

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11
Q

what is the primary extracellular osmole?

A

sodium

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12
Q

what is a quality of an effective osmole?

A

in order to exert osmotic pressure, a particle cannot cross membrane

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13
Q

how does water move between the 3 body compartments?

A

moves freely

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14
Q

how are changes in osmolar content balanced?

A

by redistribution of water

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15
Q

is urea an effective osmole?

A

no

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16
Q

is glucose an effective osmole?

A

yes unless insulin is present

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17
Q

body water is what % of males body wt? what % of females body wt?

A

60% males

50% females

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18
Q

what is normal plasma osmolarity?

A

280-290 mosm/L

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19
Q

how can we estimate plasma osmolarity (formula)?

A

formula: 2 x ([Na] + [glucose]/18 + [BUN/2.8])

if BUN is normal: 2 x ([Na] + [glucose]/20

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20
Q

if calculated osmolarity and measured osmolarity are different by more than 10 mosm/L (measured will be higher), what is probable?

A

presence of a foreign substance: alcohols, poisons

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21
Q

what is the primary determinant of plasma osmotic pressure? why?

A

albumin: confined to plasma

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22
Q

high serum Na will do what? low serum Na will do what?

A

high serum Na will draw water out of cells. low serum Na will send water into cells

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23
Q

overall, what will a change in serum Na accomplish?

A

a redistribution of total body water. not necessarily a change in absolute total body water.

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24
Q

low serum albumin can be associated with what?

A

edema, as fluid leaves intravascular space for the interstitium

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25
Q

adding K to serum will accomplish what?

A

water migrates to from extracellular space -> intracellular space;

26
Q

changes to cell volume will affect what organ in particular?

A

brain. look here first for evidence of swelling/shrinking

27
Q

hyponatremia (low serum sodium) will promote water movement in what direction?

A

into cells, increasing their volume

28
Q

how does the brain defend itself against changes in osmolarity?

A

can resist change by varying concentration of solutes other than Na and K such as inositol or AAs. glial cells can create and secrete these molecules and blunt effect of systemic change. can also remove these small molecules if needed.

29
Q

what are idiogenic osmoles?

A

the solutes that the brain can create (inositol or AAs) in order to protect itself rom systemic changes in concentration.

30
Q

how long does the production or removal of idiogenic osmoles take?

A

2-3 days

31
Q

osmolarity is monitored by what receptors, and where?

A

osmoreceptors in the hypothalamus

32
Q

increases in osmolarity as sensed by the osmoreceptors in the hypothalamus triggers what?

A

ADH release, thirst

33
Q

what does ADH stimulate?

A

water retention, peripheral vasoconstriction

34
Q

at what plasma osmolarity does ADH level begin to rise quickly?

A

right at 280, and thirst increases accordingly

35
Q

ADH released more dramatically in response to blood volume depletion or in response to hyper-osmolarity?

A

blood vol depletion trumps osmoregulation

36
Q

how is water handled in the PT?

A

water passively follows solutes

37
Q

how are water and NaCl handled in the LoH?

A

both are reabsorbed independently of each other

38
Q

how is water handled in the CT?

A

water can be reabsorbed independently of solutes (via aquaporins)

39
Q

what is the range of average urine output?

A

0.5 to 12L per day

40
Q

in the absence of ADH, will the urine be more or less dilute?

A

more dilute: in the absence of ADH, relatively dilute urine from the DCT becomes further diluted by Na reabsorbtion in the collecting tubule

41
Q

what will increase osmolarity of the renal medulla?

A

NaCl reabsorption in the LoH

42
Q

volume regulation: what senses changes in the Na flow rate?

A

Macula densa senses increased Na load (indication of incr tubular pressure) and feeds back to the afferent arteriole, which constricts in response

43
Q

volume is monitored by what receptors, and where?

A

baroreceptors in the carotid sinus sense decr arterial pressure
atrial stretch receptors sense volume expansion

44
Q

when baroreceptors in the carotid sinus sense decr arterial pressure, how do they respond?

A

stimulate the adrenergic system, release ADH

45
Q

when atrial stretch receptors sense volume expansion, how do they respond?

A

stimulate ANP release

46
Q

what does Effective Circulating Volume refer to?

A

the perfusing, bioavailable blood volume (plasma/intravascular blood: not interstitial blood)

47
Q

what compartment of the total body volume is available to stimulate baroreceptors?

A

only the plasma/effective circ volume

48
Q

hyperaldosteronism can lead to what state?

A

abnormal fluid retention, hypervolemia

49
Q

what is the typical response to low ECV (effective circ volume)?

A

incr cardiac output, incr peripheral resistance, incr intravascular volume via Na and water retention

50
Q

What does renin do?

A

cleaves angiotensinogen to angiotensin I

51
Q

what does ACE do?

A

converts angiotensin I to angiotensin II

52
Q

what are 5 actions of angiotensin II?

A
  1. direct vasoconstriction of the efferent arteriole
  2. incr Na and HCO3- reab in the prox tubule
  3. stimulates aldosterone release
  4. systemic vasoconstriction
  5. increase thirst (though ADH is the primary stimulator of thirst)
53
Q

when Na and HCO3- are reabsorbed in the PT (as a result of incr amounts of AtII), what happens to the water?

A

follows passively, resulting in isotonic fluid retention

54
Q

where is aldosterone synthesized?

A

adrenal cortex

55
Q

where does aldosterone primarily act?

A

collecting duct

56
Q

what does aldosterone do to Na and K?

A

stimulates Na channels in principle cells of collecting duct, increases Na absorption and K secretion

57
Q

what does aldosterone do to H+?

A

stimulates H+ secretion in intercalated cells

58
Q

what does ANP do to vessels?

A

1) incr. Na secretion in medullary CD
2) direct systemic vasodilator, lowers BP.
3) vasodilation of the afferent arteriole leads to increased GFR.
4) inhibits renin, aldosterone, and ADH

59
Q

what does ANP do to Na?

A

stimulates Na excretion in medullary CD

60
Q

what effect does an elevated BP have in normal patients?

A

triggers Na diuresis: increased renal blood flow causes suppression of renin release, and ANP is released. intravascular volume falls, reducing BP

M2 Renal/FEK (20 decks)

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