Regulation of Na+ Balance and ECF Flashcards
What percent of body weight is Total body water (TBW)?
60%
ICF Volume makes up what fraction of TBW?
2/3
ECF Volume makes up what fraction of TBW?
1/3
ECF is divided into what 2 components?
Plasma Volume 25%
Interstitial Fluid Volume 75%
True or False: ICFV osmolality is always equal to ECFV osmolality.
TRUE- due to passive movement of H2O
What are the major cations of ICFV?
potassium
magnesium
What are the major anions of ICFV?
phosphate
protein
What is the major cation of ECFV?
Sodium
What are the major anions of ECFV?
chloride
bicarbonate
What determines the size of ECFV?
total exchangable Na+ content (TBNa)
What affect does ingestion of Na+ have on ECFV?
Increases TBNa which Increases osmolality of ECFV
What is the effect of having an increased osmolality of the ECFV?
increased thirst, increased water intake, and increased vasopressin release to increase renal water conservation until ECFV osmolality returns to normal
What effect does having an increased ECFV osmolality have on the ICFV?
because the retention of fluid due to increased ECFV osmolality is isotonic, there is little to no change in ICFV
What effect does vomiting and diarrhea have on the ICFV and ECFV?
no real effect on ICFV, because there is an isotonic fluid loss (ECFV) with no change in ECFV osmolality or in the size of the ICFV
What does plasma sodium concentration tell you about the size of the ECFV?
nothing, per se, because the concentration is determined by the ratio of TBNa to TBW
What effect does water loss (no change in TBNa) have on the ICFV and ECFV?
2/3 would go to ICFV
1/3 would go to ECFV
What portion of ECFV perfuses all tissues of the body?
plasma volume
True or false: decreasing 6 L of H2O will decrease ECFV way more than a 2 L loss in isotonic fluid.
False- these would be about the same. If H2O was lost, it would be mostly from the ICFV (2/3)
How does one estimate of the state of ECFV and ICFV?
clinical criteria: H&P, urinary Na+, H2O excretion
What are the 5 things you can obtain from a history that will allow you to estimate ECFV and ICFV?
1) Volume depletion (isotonic)
2) Volume loss (mainly water)
3) Isotonic volume expansion
4) Hypotonic volume expansion
5) Hypertonic volume expansion
What can lead to isotonic volume depletion?
vomiting
diarrhea
poor intake
urine losses (from diuretics)
What do isotonic losses do to TBW, ECFV, and ICFV?
Decrease TBW
Decrease ECFV
no change in ICFV
What can lead to volume loss (water)?
- Lack of H2O intake
- Obligate H2O loss from urine
- Impaired renal H2O conservation
- Marked solute excretion
What do water losses do to TBW, ECFV, and ICFV?
Decrease TBW
Decrease ECFV
Decrease ICFV
What causes isotonic volume expansion? What specific conditions?
Occurs when salt and water intake exceed the ability of the kidney to excrete them
Can occur in CHF, cirrhosis, nephrotic syndrome, and renal failure
Will TBNa and TBW always increase similarly in isotonic volume expansion?
No- they can be different leading to different effects on plasma sodium concentration
What is hypotonic volume expansion?
retention of water (intake > output) with no change in TBNa
What does hypotonic volume expansion do to TBW, ECFV, and ICFV?
Increase TBW
Increase ICFV
Increase ECFV
(plamsa osmolality and Na+ conc is low)
What could cause hypertonic volume expansion?
RARE- a massive ingestion of Na+ without much H2O intake OR excessive administration of NaHCO3 in hospital
What is hypertonic volume expansion?
an increase in TBNa with normal or slightly decreased TBW
What does hypertonic volume expansion do to TBW, ECFV, and ICFV?
Increase ECFV (increased osmolality pulls it in from ICFV) Decrease ICFV Unchanged TBW
List the signs of ECFV depletion.
Increased HR Decreased BP Orthostatic tachycardia or hypotension Poor skin turgor Absence of edema
List the signs of volume expansion.
Edema (due to increased ISFV from ECFV)
JVD (distended neck veins)
Rales (increased fluid in lungs)
Cardiomegaly
Describe the urine of someone with isotonic loss.
Urine Na+ excretion is low (Na+ retention)
Urine is concentrated (high osmolality from water reabsorption; mainly urea)
What pathological settings could send neural and humoral signals to the kidney to retain NaCl and H2O?
CHF
Cirrhosis
Nephrotic syndrome
What is neutral balance?
intake = output
What is positive balance?
intake > output
What is negative balance?
output > intake
