10: Body Fluid Compartments

Question 1

Volume contraction vs expansion

Answer 1

Contraction: decrease in ECF (volume depletion)
Expansion: increase in ECF

Question 2

How much of the body’s water is ECF vs ECF

Answer 2

ICF: 66%
ECF: 33%

Question 3

Two portions of ECF and what separates them

Answer 3

Interstitial fluid (80%) + plasma (20%) - separated by capillary wall

Question 4

Other fluids of the body not considered ICF or ECF

Answer 4

Lymph, CSF, humors of eye, serous fluid, GI secretions

Question 5

60-40-20 rule of body water

Answer 5

1. 60% of body weight is total body water
2. 40% of body weight is ICF
3. 20% of body weight is ECF

Question 6

How is ECF an intermediary between cells and external evnironment?

Answer 6

All exchanges btwn cells and environment must occur thru the ECF

Question 7

Only fluid that can be acted on directly to control its volume and composition

Answer 7

Plasma

Question 8

Electrolytes vs non-electrolytes

Answer 8

1. Electrolytes: dissociate into ions in water

2. Non-electrolytes: contain covalent bonds that prevent them from dissociating in solution - have no electrical charges

Question 9

What has a greater ability to cause fluid shift - electrolytes or non electrolytes - and why?

Answer 9

Electrolytes - have higher osmotic power as they dissociate into at least two ions

Question 10

What ions are found more in ICF vs ECF?

Answer 10

ECF: Na, Cl
ICF: K, PO4, more protein anions

Question 11

Tonicity of a solution

Answer 11

The effect the solution has on cell volume - can cause it to remain the same size, swell, or shrink

Question 12

NaCl concentration of an isotonic cell environment

Answer 12

0.85% NaCl

Question 13

Predominant cation in ECF

Answer 13

Na

Question 14

What ion ECF volume mainly regulated by?

Answer 14

Na

Question 15

Na concentrations in ECF and ICF typically

Answer 15

ECF: 140 mEq/L
ICF: 5 mEq/L

Question 16

Three main solutes in ECF

Answer 16

Na, glucose, urea

Question 17

Equation for calculating serum osmolality + the “eyeball” way to do it

Answer 17

Osmolarity = 2(Na) + (glucose/18) + (BUN/2.8)

Eyeball: 2(Na)

Question 18

X and Y axes of Darrow-Yannet diagrams

Answer 18

X axis: volume in L

Y axis: osmolality in mOsm/kg H2O

Question 19

What does polyuria imply about water or solute diuresis or urine volume?

Answer 19

1. Implies water/solute diuresis of 2.5-3 L/day +

2. Urine volume of 40+ mL/kg/day

Question 20

Four mechanisms that cause polyuria

Answer 20

1. Increase fluid intake
2. Increased GFR (fever, hyper metabolic states)
3. Increased solute output (DM, hyperthyroid, use of diuretics)
4. Inability of kidney to reabsorb water in DCT (CDI, drugs, chronic renal failure)

Question 21

Water diuresis

Answer 21

Increased water exretion without corresponding increase in salt exretion

Question 22

Main causes of water diuresis

Answer 22

Increased intake of water, polydipsia, diabetes insipidus

Question 23

Solute diuresis

Answer 23

Increased water excretion concurrent with increased salt excretion

Question 24

Primary causes of solute diuresis

Answer 24

Significant increase in salt present in tubular fluid; NaCl, hyperglycemia, high protein intake, recovery from AKI