Post on 14-Dec-2015
Chapter 27
Fluid, Electrolyte and Acid-Base
Balance
ECF ICF
different ion compositionsdifferent fluid compartments
same osmotic concentration
interstitial fluidblood plasma
cytoplasm
≠
~1/3 ~2/3
Fluid basics
Fluid basics
1. all homeostatic mechanisms monitor the ECF, not the ICF
2. receptors can’t monitor [ion]but can monitor:
plasma volumeosmotic concentration
3. cells cannot actively move H2O“water follows salt”
Fluid basics
4. [water] and [electrolyte]
will rise if gains exceed losses
will fall if losses exceed gains
hormone basics
1. ADH(antidiuretic hormone)
high blood [osmotic]
release
H2O conservation in kidneystimulates thirst
hormone basics
2. Aldosterone
rising [K+]falling [Na+]renin release
released in response to:
[Na+], Cl-, H2Oreabsorption in kidney
hormone basics
3. Natriuretic hormones
block ADH releaseblock aldosterone release
released cardiac/brain cells
[Na+] and H2Olost to urine
interstitial fluid
plasma
Fluid movements
ECF
collo
idosm
oti
cp
ress
ure
hyd
rost
ati
cp
ress
ure
Fluid movements
fig 21-12
interstitial fluid
plasma
Fluid movements
ECF
collo
idosm
oti
cp
ress
ure
hyd
rost
ati
cp
ress
ure
ICF
rapid movement between ICF and ECF is called fluid shift
If [osmotic]
hypertonic
H2O
Fluid shift
ECF ICF
If [osmotic]
hypotonic
H2O
Fluid shift
ECF ICF
Fluid shift
net loss of water dehydration
sweating, vomiting, diarrhea
ICF and ECF become more concentrated
hypernatrimia
ADH, renin secretion thirst, …
give hypotonic fluids (H2O)
Fluid shift
net gain of water
into ECFinto ICF
reduce ADH secretion
increase fluid loss
Fluid shift
net gain of water
water excess (overhydration)
drinking a lotinjection of hypotonic solutionkidney or liver failureexcess ADH production
hyponatrimia
effects on CNS H2O intoxication
Electrolyte balance
electrolyte balance:
will affect H2O balancewill affect cell functions
Na+
K+
most common electrolytebalance problems
less commonmore serious
Electrolyte balance
Na+
too much ADH, retain H2O
renin-angiotensinogen retain Na+, H2O
too little ADH, lose H2O
ANP, BNP lose Na+, H2O
Electrolyte balance
K+
98% is in ICF
balance in ECF is smallmaintained by secretion in kidney
Electrolyte balance
K+
too much severe cardiacarrhythmias
too little and
100 Keys pg. 1007
“Fluid balance and electrolyte balance are interrelated. Small water gains or losses affect electrolyte concentrations only temporarily. The impacts are reduced by fluid shifts between the ECF and ICF, and by hormonal responses that adjust the rates of water intake and excretion. Similarly, electrolyte gains or losses produce only temporary changes in solute concentration. These changes are opposed by fluid shifts, adjustments in the rates of ion absorption and secretion, an adjustments to the rates of water gain and loss.”
100 Keys pg. 1019
“The most common and acute acid-base disorder is respiratory acidosis, which develops when respiratory activity cannot keep pace with the rate of carbon dioxide generation in peripheral tissues.”