Renal (Sodium/water Physiology)

Front 1

In the equation for calculating plasma osmolality, why is sodium multiplied by 2, why is glucose divided by 18, and why is BUN divided by 2.8?

Back 1

Plasma Na is multiplied by 2 to account for osmotic contribution of accompanying anions in the ECF (primarily Cl and HCO3). Conc of glucose and BUN are divided by those numbers to convert from frequently measured units of mg/dL into mmol/L.

Front 2

Which increases the osmolality of a solution more: a gram of sodium chloride, or a gram of albumin?

Back 2

a gram of sodium, but remember it only contributes to osmolality b/w cell and extracellular fluid (not at the capillary wall).

albumin does not contribute to plasma osmolality since normal plasma albumin conc of 4 g/dL represents less than 1 mOsm/kg

Front 3

plasma sodium concentration is regulated by changes in:

a. sodium balance
b. water balance
c. volume balance
d. none of the above

Back 3

B.

plasma osmolality is regulated by osmoreceptors in hypothalamus that influence release of ADH and thirst. ADH reduces water excretion while thirst increases water intake. the combined effects result in water retention, which will tend to lower plasma osmolality and plasma sodium conc by dilution. thus, regulation of plasma sodium conc is mediated almost entirely by CHANGES IN WATER BALANCE, not in the handling of sodium

Front 4

Na/K ATPase maintains ___ in the ECF and ___ in the ICF.

Back 4

Na; K

as a result, water is in steady state equilibrium b/w ECF and ICF

Front 5

addition of water to ECF does what?

Back 5

triggers the movement of water into the ICF until the osmolalities of the ECF and ICF are equal

Front 6

addition of Na to the ECF (without water...like eating a bag of salted potato chips) will do what?

Back 6

... triggers the movement of water from the ICF to the ECF until the osmolalities of the ECF and ICF are equal)

Front 7

EABV/PLASMA OSMOLALITY is regulated by sodium balance.

Back 7

EABV (effective arterial blood volume)

Front 8

EABV/PLASMA OSMOLALITY is regulated by balance of water intake and/or clearance.

Back 8

plasma osmolality

Front 9

Too much water = HYPONATREMIA or HYPERNATREMIA?

Back 9

hyponatremia (decrease osmolality)

Front 10

Excess Na = EXPANSION or CONTRACTION of ECF?

Back 10

expansion (Na will go to ECF and increase plasma osmolality, drawing water out of ICF until equilibrium is re-established)

Front 11

which of the following is NOT found mostly in the ECF?

a. Na
b. K
c. Ca
d. HCO3

Back 11

B.

Front 12

what does osmolar gap suggest?

Back 12

it is an indication that there is something else dissolved in the serum that is producing an osmol gap, which can be a major clue in determining what is ailing the patient.

Front 13

name some possible things that could be present in the serum of a pt with osmolar gap

Back 13

THINGS PTS TAKE:
- methanol
- ethanol
- isopropanol
- ethylene glycol (anti-freeze)

THINGS DOCTORS GIVE TO PTS
- mannitol
- contrast media
- glycine

Front 14

what's the difference b/w effective and non-effective solutes?

Back 14

effective solutes = solutes that are confined to one compartment and can cause water shift b/w ECF and ICF (ie. contrast media, mannitol)

non-effective solutes = solutes that are membrane permeable and equilibrate b/w ICF and ECF (so don't cause water shift) .. ie. urea, ethanol, methanol, etc

Front 15

most body fluids are hypotonic (meaning that the Na, K, Cl contents in these fluids are lower than the conc in the serum). which body fluid is the only one that is isoosmolar or slightly hyperosmolar?

Back 15

bile

Front 16

the loss of what two body fluids will produce acidosis in addition to water loss?

Back 16

bile and diarrhea (due to their high bicarbonate content, there will be over accumulation of serum protons in the case of acute loss of these fluids...leading to metabolic acidosis)

Front 17

_______ is the primary determinant of the size of the ECF.

Back 17

Sodium!!

Front 18

what will happen to ECF and ICF volume when you give isotonic fluid (saline)?

Back 18

only ECF volume will increase; ICF volume will remain unchanged

Front 19

addition of hypotonic soln (0.45% NaCl) to ECF will do what?

Back 19

cause movement of water into ICF

Front 20

addition of hypertonic soln (3% NaCl) to ECF will do what?

Back 20

cause movement of water out of ICF into ECF

Front 21

how will addition of pure water (without sodium) affect ECF and ICF volumes?

Back 21

will increase ECF and ICF volumes equally

Front 22

which is better to give to a pt in order to restore intravascular volume? Why?

a. D5W
b. normal saline

Back 22

B.
adding D5W is like adding pure water, which will distribute 2/3 to ICF and 1/3 to ECF.

all of the saline will stay in the ECF and won't go into ICF at all. this will be an excellent way to restore intravascular volume since 1/4 of an entire liter of fluid will enter intravascular volume.

Front 23

what is the difference b/w EABV and ECF?

Back 23

EABV = unmeasurable parameter that refers to the part of ECF that is in the arterial system and is therefore EFFECTIVELY PERFUSING vital organs (like the kidney); it is governed by baroreceptors rather than osmoreceptors

ECF = fluid that is in extracellular space; they are divided into two compartments: interstitial fluid that bathes the cells and the intravascular compartment of circulating plasma water (These spaces are separated by capillary wall).

Front 24

in hypovolemia due to vomiting, what happens to ECF and EABV?

Back 24

ECF and EABV both decrease

Front 25

what happens to ECF and EABV in CHF?

Back 25

EABV is low due to poor cardiac output, ECF is expanded bc of the activation of sodium-retaining hormones (in an attempt to increase perfusion towards normal), which eventually leads to edema formation and increases plasma volume

Front 26

a FENA of <__% tells you that the kidney sees diminished ECF or that you have low EABV (the kidney can't distinguish bw the two)

Back 26

1%

Front 27

pt gets 2L H2O, what will happen to urine Na?

what if pt gets 400 ml 3% NaCl?

what if pt gets 1 L normal saline?

Back 27

goes up in all three cases; due to the fact that urine Na reflects EABV, not necessarily serum Na. so as long as the EABV goes up, you'll have more urine Na.

a high EABV is assoc with decreased Na uptake (Na retentive hormones shut off + ANP release --> leading to natriuresis and diuresis)

Front 28

low EABV will cause urine Na to INCREASE/DECREASE

Back 28

decrease; bc low EABV will induce more hormones (like ADH) to retain more Na in the kidneys

Front 29

ANP is produced by the heart (atria) in response to stretch (volume expansion) and works on kidneys to induce natriuresis (Na excretion). It is a reliable marker for heart failure, but has little usefulness in tx of Na retention. Why?

Back 29

there are compensatory pathways that offset its action

CHF is a condition where kidneys will sense low EABV (even if it's not really a volume depletion problem, but rather a cardiac output issue).
The stimulus for ADH release in low EABV (due to baroreceptors in afferent arterioles) will over-ride the stimulus to shut-off ADH (due to osmoreceptors in the hypothalamus) when the osmolality is low (aka. when ECF is actually high in the case of CHF)!

Front 30

why does low EABV give you a low FENA?

Back 30

low EABV will mean low effective perfusion to vital organs (ie. kidneys), which means low GFR and low Na delivery to distal nephron sites and urine --> low FENA

Front 31

to check ECF volume status, one only needs to do a physical exam. name some common signs and sx's.

Back 31

skin turgor, moisture of mucous membranes, orthostatics, CVP (which is pretty much a JVP)