Regulation of Na+ Balance and ECF

Question 1

What percent of body weight is Total body water (TBW)?

Answer 1

60%

Question 2

ICF Volume makes up what fraction of TBW?

Answer 2

2/3

Question 3

ECF Volume makes up what fraction of TBW?

Answer 3

1/3

Question 4

ECF is divided into what 2 components?

Answer 4

Plasma Volume 25%

Interstitial Fluid Volume 75%

Question 5

True or False: ICFV osmolality is always equal to ECFV osmolality.

Answer 5

TRUE- due to passive movement of H2O

Question 6

What are the major cations of ICFV?

Answer 6

potassium

magnesium

Question 7

What are the major anions of ICFV?

Answer 7

phosphate

protein

Question 8

What is the major cation of ECFV?

Answer 8

Sodium

Question 9

What are the major anions of ECFV?

Answer 9

chloride

bicarbonate

Question 10

What determines the size of ECFV?

Answer 10

total exchangable Na+ content (TBNa)

Question 11

What affect does ingestion of Na+ have on ECFV?

Answer 11

Increases TBNa which Increases osmolality of ECFV

Question 12

What is the effect of having an increased osmolality of the ECFV?

Answer 12

increased thirst, increased water intake, and increased vasopressin release to increase renal water conservation until ECFV osmolality returns to normal

Question 13

What effect does having an increased ECFV osmolality have on the ICFV?

Answer 13

because the retention of fluid due to increased ECFV osmolality is isotonic, there is little to no change in ICFV

Question 14

What effect does vomiting and diarrhea have on the ICFV and ECFV?

Answer 14

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

Question 15

What does plasma sodium concentration tell you about the size of the ECFV?

Answer 15

nothing, per se, because the concentration is determined by the ratio of TBNa to TBW

Question 16

What effect does water loss (no change in TBNa) have on the ICFV and ECFV?

Answer 16

2/3 would go to ICFV

1/3 would go to ECFV

Question 17

What portion of ECFV perfuses all tissues of the body?

Answer 17

plasma volume

Question 18

True or false: decreasing 6 L of H2O will decrease ECFV way more than a 2 L loss in isotonic fluid.

Answer 18

False- these would be about the same. If H2O was lost, it would be mostly from the ICFV (2/3)

Question 19

How does one estimate of the state of ECFV and ICFV?

Answer 19

clinical criteria: H&P, urinary Na+, H2O excretion

Question 20

What are the 5 things you can obtain from a history that will allow you to estimate ECFV and ICFV?

Answer 20

1) Volume depletion (isotonic)
2) Volume loss (mainly water)
3) Isotonic volume expansion
4) Hypotonic volume expansion
5) Hypertonic volume expansion

Question 21

What can lead to isotonic volume depletion?

Answer 21

vomiting
diarrhea
poor intake
urine losses (from diuretics)

Question 22

What do isotonic losses do to TBW, ECFV, and ICFV?

Answer 22

Decrease TBW
Decrease ECFV
no change in ICFV

Question 23

What can lead to volume loss (water)?

Answer 23

• Lack of H2O intake
• Obligate H2O loss from urine
• Impaired renal H2O conservation
• Marked solute excretion

Question 24

What do water losses do to TBW, ECFV, and ICFV?

Answer 24

Decrease TBW
Decrease ECFV
Decrease ICFV

Question 25

What causes isotonic volume expansion? What specific conditions?

Answer 25

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

Question 26

Will TBNa and TBW always increase similarly in isotonic volume expansion?

Answer 26

No- they can be different leading to different effects on plasma sodium concentration

Question 27

What is hypotonic volume expansion?

Answer 27

retention of water (intake > output) with no change in TBNa

Question 28

What does hypotonic volume expansion do to TBW, ECFV, and ICFV?

Answer 28

Increase TBW Increase ICFV Increase ECFV (plamsa osmolality and Na+ conc is low)

Question 29

What could cause hypertonic volume expansion?

Answer 29

RARE- a massive ingestion of Na+ without much H2O intake OR excessive administration of NaHCO3 in hospital

Question 30

What is hypertonic volume expansion?

Answer 30

an increase in TBNa with normal or slightly decreased TBW

Question 31

What does hypertonic volume expansion do to TBW, ECFV, and ICFV?

Answer 31

``` Increase ECFV (increased osmolality pulls it in from ICFV) Decrease ICFV Unchanged TBW ```

Question 32

List the signs of ECFV depletion.

Answer 32

``` Increased HR Decreased BP Orthostatic tachycardia or hypotension Poor skin turgor Absence of edema ```

Question 33

List the signs of volume expansion.

Answer 33

Edema (due to increased ISFV from ECFV) JVD (distended neck veins) Rales (increased fluid in lungs) Cardiomegaly

Question 34

Describe the urine of someone with isotonic loss.

Answer 34

Urine Na+ excretion is low (Na+ retention) | Urine is concentrated (high osmolality from water reabsorption; mainly urea)

Question 35

What pathological settings could send neural and humoral signals to the kidney to retain NaCl and H2O?

Answer 35

CHF Cirrhosis Nephrotic syndrome

Question 36

What is neutral balance?

Answer 36

intake = output

Question 37

What is positive balance?

Answer 37

intake > output

Question 38

What is negative balance?

Answer 38

output > intake