Katz: Body Fluid Compartments Flashcards Preview

CRAAB 6 > Katz: Body Fluid Compartments > Flashcards

Flashcards in Katz: Body Fluid Compartments Deck (39):

What are the three separate body fluid compartments?

Interstitial fluid
intracellular fluid


What is the composition of plasma?

Water with a concentration of 55,500 mM


What is the osmolarity of plasma?



Why is albumin important in plasma?

It's a BIG ANION that opposes capillary leak (net filtration)

It also carries and is in equilitbrium with: Ca, fatty acids, H and many drugs.


How may net negative charges does albumin have?



What is primarily responsible for the anion gap? What is the anion gap normally?




What is the equation for the anion gap?

Na- (Cl + HCO3)


What is the main difference between the composition of the interstitial fluid and plasma?

Interstitial fluid is just plasma WIHTOUT albumin


What is the capillary wall permeable and not very permeable to?

Permeable: water, Na, Cl

Not permeable to albumin


Why are capillaries expected to leak?

Capillaries contain plasma under pressure and they have pores


Why don't capillaries not leak as much as expected?

Albumin (relatively impermeable anion) provides a FORCE (protein oncotic pressure) that prevents the hydraulic/hydrostatic capillary pressure from pushing plasma out through the capillary pores.


What is the equation for fluid movement across a capillary wall?

Forces favoring filtration - forces favoring resorption
Kf (Pc + Oif)- (Pisf + Ocap)


What is the approximate concentration of solutes in cells?

300 mM total solutes/L


Why are Na/K pumps present on all cells?

Cells use the Na/K pumps to maintain cell volume!


What happens if cells DON'T have Na/K pumps?

They increase in volume and lyse...this is bad.


What is the Na/K pump?

A cell membrane system that directly hydrolyzes ATP to move solute up the electrochemical gradient (primary active pump)


What is osmolarity?

The total free solute concentration measures as mM of total free solute/L


What is mOsms?

The units of osmolarity (mM of total free solute)


What does isosmotic mean?

When a solution is approximately 300 mOsms (292).


What is the osmolality of plasma closer to 292 mOsms rather than 300?

Both of these DECREASE the conc of free solutes
1. Ca binds albumin
2. Na binds Cl = ion pairing>


What does isotonic mean?

Any solution that does NOT change cell volume ( it needs 300 mOsms) of impermeable solutes


What does isoncotic mean?

Any solution with 1mM plasma albumin, or any solution with a PROTEIN OSMOTIC PRESSURE of approximately 25 mmHg (anion gap of 17).


What causes protein osmotic pressure?

D/t 1 mM plasma albumin (4.5 g albumin/ 100mL) and a semi-permeable capillary wall that is relatively impermeable to albumin. Plasma protein ATTRACTS interstitial fluid INTO the plasma compartment.

The MAGNITUDE of the attraction is PROTEIN OSMOTIC PRESSURE of plasma.


What is protein osmotic pressure?

Approximately 25 mmHg

The hydrostatic pressure required in the plasma compartment to prevent interstitial fluid from moving INTO the plasma compartment.


What percent of a normal person's body weight is d/t water volume?



When you drink water, how does it distribute into the body fluid compartments?

It distributes into ALL 3 compartments (through pores and aquaporins) in PROPORTION to the VOLUME of the compartment.

Water is absorbed from the GI tract into the plasma. The increased concentration of water increases the capillary pressure and water distributes through pores down it's gradient to the ISF. The increased water concentration also decreases the osmotic pressure (albumin) further supporting greater filtration.

The increased conc of water in the ISF than moves down it's conc gradient through aquaporins into the cell. Resulting in distribution into all 3 compartments.


How is a normal saline iv distributed throughout the body? Why?

Plasma and ISF only

A saline Iv increases the capillary pressure and decreases the oncotic pressure leading to increased filtration into the ISF. Na is actively pumped out of the cell so it remains isotonic. Fluid distribution in the plasma and ISF is again proportional to the volumes of the compartment.

Na/K pumps


What do you give to someone who has secretory diarrhea?

It is approximately the SAME as loss of isosmotic (normal) saline.

If you lose 10 L of water/saline through diarrhea>
give them 10 L saline>
Goes to the same compartments from which you lost the fluid (ISF and Plasma)


How does 1/2 normal saline distribute in the body?

Half distributes as WATER and HALF as normal saline. More water goes into the cells than normal saline, but not as much as just drinking water.


What bodily function is equivalent to the loss of 1/2 normal saline?



What can you give someone who has fainted after a marathon?

1/2 normal saline...give them what they lost


What is isoncotic saline?

1mM albumin in normal saline

"Artificial plasma" --not as expensive as blood, but it's still expensive to make recombinant albumin


How does Isoncotic saline distribute?

Primarily in the plasma compartment especially during hypovolemia

Isooncotic saline>
increase in capillary pressure>
filtration of water>
increase in concentration of Alb>
resorption of water


What solution should you use if you want to get someone's BP up quickly?

Isoncotic saline


What does D5W consist of? What type of solution is it?

5 grams glucose/100 ml water > aproximately 300 mM



Where does D5W distribute to in the body?

It is just like WATER and distributes to all 3 compartments in proportion to the volume of the compartments.

Dextrose iv>
increased capillary pressure/decrease osmotic pressure>
increased water ISF>
water/glucose get transported into cell>
glucose is oxidized, turned into glycogen/fat>
leaves water distributing to all 3 compartments


Why does D5W distribute in the body like water?

Glucose is COMPLETELY REMOVED (oxidation, glycogen, fat) leaving only water.


What is the difference between giving D5W and water?

You can give D5V to an unconscious person through an IV


In the case of hypovolemia, most solutions will distribute proportionally more w/in the plasma compartment...why?

When a pt is hypovolemic they have low capillary pressure to begin with so adding fluids doesn't increase pressure enough to cause filtration so the solution stays in the plasma.