Physiology: Body Fluid Compartments

Front 1

What's the makeup of our body fluids?
How much is TBW?
Intracellular Fluid?
Extracellular Fluid?
Interstitial Fluid?
Intravascular fluid?

Back 1

Front 2

Another way of visualizing our body fluid makeup:
What % of us is solid?
What % of us is fluid?
What are the major intracellular electrolytes (3) ?
What are the major extracellular electrolytes (2) ?

Back 2

Front 3

What's the distribution of electrolytes in the body fluid compartments?

What is the major difference (what are the most important cations and where do they dominate)?

Back 3

*Extracellular is mostly Na.
*Intracellular is mostly K.

Front 4

What the relationship between osmolality and total body water?

Back 4

*When you change one compartment, you change them all. More osmolality means more body water.

Front 5

Are cell membranes and vasculature permeable to water? Any exceptions?

What kinds of substances can cross membranes?

What kinds of substances can't as easily get through?

Back 5

*Cell membranes and vasculature are freely permeable to water (except for parts of the distal nephron).

*Urea and alcohols, as well as many drugs, can freely cross most membranes.

*Glucose and sodium may cross membranes, but only via channels which are selectively permissive.

Front 6

Describe what would occur if you were to add 1.5L of isotonic saline to the extracellular fluid.

Back 6

*Since the isotonic saline is the SAME osmolality as the ICF/ECF, you just increase the volume of the ECF. No water is lost from the ICF, because there's no need to adjust the osmolality.

Front 7

What would occur if you added 1.5L of pure water to the ECF?

Back 7

*The water would distribute evenly in ECF and ICF.
*The Na and K concentrations decrease slightly, because you're diluting them.
*Volumes change as well, 2/3 intracellular and 1/3 extracellular, just like the body's normal fluid makeup.

Front 8

What would occur if you added pure salt?

Back 8

*Na will preferentially expand the ECF, because that's where Na hangs out.
*[Na] of the ECF will increase transiently, causing water to shift from the ICF to the ECF. This maintains the osmolality between the two.
*TBW hasn't changed, but its distribution b/t the two compartment has changed. The ICF has shrunk.

Front 9

What would happen here if you were a diabetic and you added a bunch of glucose to the ECF (ate an entire box of powdered sugar like the dirty little pig you know you are)?

Back 9

*Water shifts from the ICF to the ECF to maintain osmolality b/t the two.
*With more water in the ECF, [Na] decreases.
*With less water in the ICF, [K] goes up.
*In a non-diabetic, you'd be able to take glucose up into the cells and equalize the fluid levels.

Front 10

What is an ineffective osmole and what would happen if you consumed a bunch of one?

Back 10

*Alcohol is a good example. Ineffective osmoles can go wherever they want, so they increase the total osmolarity of the ECF and ICF equally.
*[Na] and [K] both decrease slightly.

Front 11

A 40 year-old man appears in the emergency room following a gun shot wound. He is actively bleeding from a penetrating wound in the femoral region. Blood pressure is 70/40 and pulse 140.

While you are examining him, the nurse asks you for “orders” on this patient. What do you give?

Back 11

*Answer: 1 liter packed RBCs.
*Blood (particularly cells) will localize to the intravascular space and have the greatest effect to raise blood pressure.
*Other fluids will have a larger volume of distribution and therefore, not as much of an impact on blood pressure.
*This is totally not what Marino said during the cardio block, but I don't know...just go with it?

Front 12

A 40 year-old man appears in the emergency room following a gun shot wound. He is actively bleeding from a penetrating wound in the femoral region. Blood pressure is 70/40 and pulse 140.

While you are examining him, the nurse asks you for “orders” on this patient. Packed RBCs are NOT available!

What do you give?

Back 12

*The important thing to do is increase volume in the ECF, not the ICF, since the ECF will increase the plasma volume!

*“Normal saline” is your choice. It contains the highest concentration of Na and is “isotonic,” will distribute entirely in the ECF. Hence the ECF will be expanded by 1 liter. Approximately 25% (250 ml) will expand the plasma volume. 

*½ Normal saline has half the Na content. Hence, half will be distributed in ECF (500 ml) of which 25% (125 ml) will expand the plasma.

*½ normal saline with KCl will distribute in a similar fashion. Since K is an intracellular cation, it will obligate the distribution of water into the IC and not the EC compartment

*5% glucose in water is the same as administering water alone, since the glucose is immediately metabolized.

*Water will distribute in the total body water compartment. Hence ~ 1/3 will distribute in ECF (~300 ml) and 25% of that will distribute in plasma (75 ml).

*Distilled water cannot be administered intravenously since the hypoosmolarity will result in LYSIS of RBCs.