1. Fluid, Electrolyte and Acid-Base Balance
Chapter 27
Fluid, Electrolyte and Acid-Base Balance

2. ≠ Fluid basics ECF ICF interstitial fluid blood plasma cytoplasm ~1/3
~2/3
different ion compositions
different fluid compartments
same osmotic concentration

3. Fluid basics
all homeostatic mechanisms monitor the ECF, not the ICF
2. receptors can’t monitor [ion]
but can monitor:
plasma volume
osmotic concentration
3. cells cannot actively move H2O
“water follows salt”

4. Fluid basics
4. [water] and [electrolyte]
will rise if gains exceed losses
will fall if losses exceed gains

5. hormone basics
1. ADH (antidiuretic hormone)
high blood [osmotic]
release
H2O conservation in kidney
stimulates thirst

6. hormone basics
2. Aldosterone
released in response to:
rising [K+]
falling [Na+]
renin release
[Na+], Cl-, H2O
reabsorption in kidney

7. hormone basics
3. Natriuretic hormones
released cardiac/brain cells
block ADH release
block aldosterone release
[Na+] and H2O
lost to urine

8. Fluid movements ECF interstitial fluid plasma hydrostatic pressure
osmotic
pressure
colloid
hydrostatic
pressure

9. Fluid movements
fig 21-12

10. rapid movement between ICF and ECF is called fluid shift
Fluid movements
ECF
ICF
interstitial fluid
plasma
rapid movement between ICF and ECF is called fluid shift
osmotic
pressure
colloid
hydrostatic
pressure

11. Fluid shift
ECF
ICF
If [osmotic] 
hypertonic
H2O

12. Fluid shift
ECF
ICF
If [osmotic] 
hypotonic
H2O

13. 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)

14. Fluid shift
net gain of water
into ECF
into ICF
 reduce ADH secretion
 increase fluid loss

15. Fluid shift
net gain of water
water excess (overhydration)
drinking a lot
injection of hypotonic solution
kidney or liver failure
excess ADH production
 hyponatrimia
effects on CNS H2O intoxication

16. Electrolyte balance
electrolyte balance:
will affect H2O balance
will affect cell functions
Na+
most common electrolyte
balance problems
less common
more serious K+

17. Electrolyte balance
Na+
too much
 ADH,  retain H2O
renin-angiotensinogen
 retain Na+, H2O
too little
 ADH,  lose H2O
ANP, BNP
 lose Na+, H2O

18. Electrolyte balance K+
98% is in ICF
balance in ECF is small
maintained by secretion in kidney

19. Electrolyte balance K+
too much
severe cardiac
arrhythmias
too little
 and


20. 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.”

21. 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.”