Body Fluid compartments

Question 1

Anion gap = ?

Answer 1

Serum Na+ - (Cl- + HCO3-)

**essentially the difference between positive and negative charges in the plasma

**plasma is neutral due to presence of negatively charged albumin which makes up for the “gap”

Question 2

Normal plasma osmolality:

Answer 2

~300 mM/L

Question 3

Define osmolality:

Answer 3

total free solute (mM) / kg of solvent

Question 4

Define osmolarity:

Answer 4

total free solute (mM) / L of solvent

Question 5

Osmolarities of Plasma solutes:

Answer 5

Na+: 140 (mM/L)

Cl-: 105

HCO3-: 25

Urea: 6

Weak organic acids: 6

Gluc: 5 (~90 mg)

K+: 4

Ca++: 4

Mg+: 1

H2PO4-: 1

Albumin: 1

Total: 296

Question 6

Interstitial fluid is plasma without____?

Answer 6

albumin

Question 7

Under normal circumstances, capillary hydrostatic pressure is opposed equally by_________.

Answer 7

capillary oncotic pressure (albumin)

**both are ~25mmHg

Question 8

Why is intracellular space so different in composition from vascular and interstitial space?

Answer 8

Only water passes freely (AQUAPORINS).

Ions controlled by ATPases.

More potassium (140 mM/L)

Less sodium (~10 mM/L)

Question 9

Isosmotic refers to?

Answer 9

Any solution with ~300 mM/L (mOsmos)

Question 10

Isotonic refers to?

Answer 10

Any solution that will not change the volume of the cell (contains 300 mOsmos of impermeable solute)

Question 11

Isoncotic refers to:

Answer 11

Any solution with protein oncotic pressure of 25 mmHg

Question 12

% of total body volume made up of water?

Answer 12

60

Question 13

Approximate distribution of total body water in L for 70 kg person:

Answer 13

Intracellular: 28 L (66%)

Extracellular: 14 L (33%)

  Interstitial: 11 L

  Plasma: 3 L

Total: 42 L (28+14)

Question 14

Composition of normal saline:

Answer 14

154 mOsmol Na
154 mOsmol Cl

so this is isosmotic and isotonic – will not enter intracellular space

Question 15

A few indications for NS:

Answer 15

DKA

Sepsis

Diarrhea (loss of Na/Cl)

Question 16

Half NS distribution?

Answer 16

half like NS, half like H2O

Question 17

Distribution of D5?

Answer 17

just like water

Question 18

Will giving NS change the plasma Na concentration?

Answer 18

No

but it will increase plasma volume because Na will not distribute intracellularly