11. Body Fluid Compartments Flashcards
what is the 60-40-20 rule
60% of body weight = Total Body Weight (TBW)
40% of weight (or 2/3 TBW) = Intracellular fluid compartment (ICF)
20% of weight (or 1/3 TBW) = Extra__cellular fluid compartment (ECF)
what two compartments make up the ECF
plasma = 1/4 *ECF
intestitial fluid = 3/4 *ECF
which compartment can be acted on directly to control vol & composition
plasma
–> then interstital fluid will be regulated too
How do the numbers of fluid intake compare to fluid loss
should match!
total intake = 2300
total loss should be 2300 too (out of this urine is biggest contributer =1400)
what happens to fluid intake and loss during exercise
increase loss of fluid bc of sweat
reduced urine output
output increases ALOT
-so you need to hydrate to match what you lost!!
what is third spacing
third space is apart of ECF, usually minimal fluid there
but too much fluid shift from blood vessels (intravascular) into nonfxnal area => fluid trapped
-ascites, interstitial area around lungs –> pul edema, burn pts, liver disease
what is selectivity
fluid compartments are semipermeable
so using osmosis, h2o moves from high [h2o] to low
trying to match dilution / [solute]
what is the ionic and nonelectrolyte composition of ICF
K+, Mg2+
proteins and organic phosphates
what is the ionic & nonelectrolyte distribution in ECF & how is it divded btn the 2 compartments
Na+, Cl-, & HCO3-
plasma: whats above plus proteins
interstital fluid: whats above but lower than whats in plasma
why is regulation of ECF important
helps regulate BP
maintain via salt balance; so osmolarity is closely regulated to prevent swelling/shrinking of cell
compare the electrolyte composition of ECF & ICF
ICF: proteins that cant permeate, PO43-, primary cation = K+
ECF: Cl-, HCO3-, primary cation = Na+
what are nonelectrolytes
molecules w/ covalent bonds that prevent them from dissociating in sol’n
no electrical charge
=glu, lipids, urea
what are electrolytes
dissociate into ions in water –> gives them higher osmatic power than nonelectrolytes
NaCl, MgCl2, etc
greater ability to cause fluid shift
what is osmolality vs osmolarity
osmolality = osmotically active particles per kg of h2o
osmolarity = osmotically active particle per L of total soln
what are the normal ranges for
Na
K
HCO3-
albumin
glu (fasting)
serum osmolality
Na = 135-147
K = 3.5 - 5.0
HCO3- = 22-28
albumin = 3.5 - 5.5
glu (fasting) = 70-110
serum osmolality = 285 - 295
what are the 4 mechanisms that can cause polyuria
- increase intake (stress/anxiety, DI)
- increased GFR (hyperthyroid, fever)
- increased output of solutes (DM, hyperthyroid, hyperparathyroid)
- inabilty of kidney to reabs in DCT (CRF, drugs)
what can cause oliguria
dehydration, blood loss, diarrhea, kidney disease, enlarged prostate
what can cause anuria
kidney failure, obstruction (stone or tumor)
what is the difference btn water diuresis & solute diuresis
both = increase h2o excretion
water diuresis = W/O increased salt excretion
solute (osmotic) = WITH increased salt excretion
what is free water clearance,
how do you calculate & what do the results mean
Ch2o = rate at which solute free h2o excreted
if positive = dilute urine
if negative = concentrated urine, conserving h2o
(if urine osm > plasma osm, free water clearance = neg bc h2o conserved)
how do you measure the amount of fluid in compartments
= dilution method
- dye distributed in body fluid compartment based on characteristics
- allow dye to equilibrate
- remove plasma & meaure [marker]
- calculate -> vol of distribution = amount injected/ [] in plasma
amount injected = amoutn injected - amount excreted in urine!
what are the indicators used for each compartment
TBW = isotopic water (d2o, 3h2o, 2h2o, antipyrine)
ECF = mannitol, inulin, sulfate, 22Na
plasma = 125I-albumin, evans blue dye
ICF & interstitial fluid cant be directly measured
how do you measure plasma (serum) osm
normal = 285-295
& estimating way = 2 * [plasma Na]
what is the Gibbs-Donnan Effect
plasma contain proteins (-) = impermeable so they create oncotic gradient && create electrival environment
both favoring movement of h2o INTO cell
what happens if gibb-donnan effect isn’t countered
cell swell –> death
prevent this by Na/K ATPase - 3 Na in & 2 K out ==> prevent excess inward h2o
what forces play a role in h2o movement btn ICF & ECF
how does the movement occur
osmotic forces
-h2o diffuse thru capillary walls & P diff btn inside & outside vessel help fluid move freely
what are the Ps close to the arteriole & venule ends of the caps
& what do the promote
arteriole end - cap BP > plasma colloid osmotic P ==> filtration
venule end - cap BP < plasma colloid osmotic P ==> absorption
occationaly extra fluid out of cap and into lymphatic vessels
what are two causes that lead to edema
- change in hemodynamic –> increase filtration - noticed when interstitial vol increased by 2.5-3 L (ie CHF, liver failure)
- renal retention of dietary Na & h2o expansion of ECF vol (ie primary renal disease)
what is an isotonic cell environment & what happens to the cell
environment has [NaCl] = 0.85%
equal movement of h2o in & out cell
what happens to a cell in a hypertonic enviornment
[NaCl] > 0.85%
net movemnt out of the cell –> cell will shrink
what happens to a cell in a hypotonic environment
[NaCl] < 0.85%
net movement of h2o into cell –> cell swells
How can plasma content change?
- ECF vol los –> increase [plasma protein] - concentrated
- ECF vol gain –> decrease [plasma protein] -dilute
what will increase Hct
ECF vol loss - concentrated
ICF vol gain - swelling of RBC
what leads to decreased Hct
ECF vol gain - dilute
ICF vol loss - shrinkage of RBC
what are crystalloids
used in replacement therapy
contain organic/inorganic salts dissolved in sterile h2o –> DO NOT cross plasma mem & stay in ECF
use glucose & NaCl
(ie 0.9% NaCl normal saline & lactated Ringers (LR))
what are colloids
used in replacement therapy
-contain large molecules that don’t pass thru semipermeable mem –> stay in intravascular compartment
so fluid out of extravascular space to balance out
ie hydroxyethyl startches & albumin
what happens when you have increased fluid loss?
hemorrhage vomitting, diarrhea
loss of isosmotic fluid
-decrease ECF vol
NOT osm bc fluid lost = isosmotic –> so no need to change ICF vol
what happens to ECV & ICV with water deprivation (increased sweating & no intake)
sweat = hypotonic
soln compared to ECF
ECF vol decrease & osm increases –> which cause h2o shift from ICF into ECF until ICF osm increases & is = to ECF osm
new steady state –> ECF & ICF vol decreased & osm increased
what happens to ECF & ICF in hyponatremia
serum Na < 130-135
decrease ECF osmotic P –> h2o moved into cell –> hypovolemia & cellular swelling
-increase ICF vol can cause edema, brain cell swelling, irritablility, depression, confusion, weakness, M cramps, anorexia, nausea & diarrhea
what happens with hypernatremia
serum Na > 147-150
h2o moves from ICF to ECF –> intracell dehyrdation & shinkage
increased ECF vol –> edema & increased BP
high Na levels - M weakness, hyperactive reflexes
decreased ICF - thirst, decrease urine output, confusion and ultimately coma
what is the difference btn vol contraction vs expansion
contraction - decreased ECF fluid –> cause decrease blood vol & BP
expansion = increased ECF fluid –> increase BP & cause edema
what occurs when you have hypotonic fluid loss?
dehydration, DI & alcoholism
= hyperosmotic vol contraction
decrease ECF & ICF vol & increase osm for both
what happens to ECF & ICF in adrenal insufficiency
=hyposmotic volume contraction
-excess NaCl in urine –> ECF osm decrease –> cause osm difference & h2o move from ECF to ICF until osm match
ICF vol increased & osm decreased
what happens during isotonic vol expansion
ie infusion of isotonic NaCl
ECF vol increase (nothing else)
what occurs w/ hypertonic vol expansion
high NaCl intake
increase ECF vol –> increase ECF osm - flow ICF to ECF
decrease ICF vol & increase osm
what happens in pts w/ SIADH
(similar effects for excess water drinking)
= hyposmotic vol expansion
increase ECF & ICF vol & decrease both osm
Pts w/ CHF have low effective circulating vol bc decreased CO. What occurs to counteract this
- activation of RAAS
- stimulation of sym NS bc baroreceptor detect decrease P
- increase ADH secretion
- increase renal fluid retention
–> edema, retain Na, increase ECF vol but dont correct effective circulating vol
what happens if ECF vol is expanded
renal NaCL & h2o excretion increased
(opposite if ECF vol contracted)
when vascular & body fluid dynamics change, what systems are called into play
renal sym Ns (decrease NaCl excretion)
RAAS (decrease NaCl excretion)
ADH (decrease h2o excretion)
ANP/BNP/urodilatin (incease NaCl excretion & reduce renin & ADH secretion)
