WATER, ELECTROLYTE, AND ACIDBASE BALANCE

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WATER, ELECTROLYTE, AND ACID-BASE BALANCE

• Body fluid compartments
• Fluids are in constant motion
• Fluid balance and water
• Water gain and loss
• Regulation of fluid intake (thirst)
• Regulation of fluid output
• Electrolytes vs. nonelectrolytes
• Functions of electrolytes
• Electrolyte distribution
• Exchange of water across capillaries
• Exchange of water across cell membranes
• Acid-base balance

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BODY FLUID COMPARTMENTS
Intracellular fluid (67) Extracellular fluid
(33)
body weight
interstitial fluid (80) plasma (20) other fluids
40 solids
67 ICF
80 interstitial fluid
60 fluids
33 ECF
20 plasma
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FLUIDS ARE IN CONSTANT MOTION
Semi-permeable membranes separate the fluid
compartments Fluids are in constant motion
between the 3 compartments
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FLUID BALANCE AND WATER
What does the term fluid balance mean?
What is the primary mechanism by which water
moves from one compartment to the next?
What controls osmosis and therefore fluid balance?
Fluid balance, then, means water balance, and it
implies electrolyte balance as well the
two are inseparable.
Water makes up 45 75 of total body weight, the
exact percentage depending upon
age newborn 75, lean adult man 60, old
age 45 body size obese as little as 45,
very lean as much as 75 gender lean adult man
60, lean adult women 50
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WATER GAIN AND LOSS
2,500 ml/day Water gain
preformed water metabolic water
Water loss
insensible loss
sensible insensible
sensible loss
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REGULATION OF FLUID INTAKE (THIRST)
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REGULATION OF FLUID OUTPUT
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ELECTROLYTES VS. NON-ELECTROLYTES
Electrolytes have a greater effect on osmosis
than do nonelectrolytes. Consider the following
C6H12O6 in water C6H12O6 in water NaCl in water
Na and Cl- in water CaCl2 in water Ca and
Cl- and Cl- in water
Which of these compounds will exert the greater
effect on osmosis?
Just as important, once the electrolyte
dissociates, its component ions attract other
ions of the opposite charge, creating an
electrochemical gradient that then adds to the
osmotic effect.
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FUNCTIONS OF ELECTROLYTES
Essential minerals Exert osmotic influences Help
maintain acid-base balance Carry electrical
current
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EXCHANGE OF WATER ACROSS CAPILLARIES
Exchange of water between plasma and interstitial
fluid occurs across capillary membranes in what
three ways?
osmosis vesicular transport bulk flow
Bulk flow is dependent upon which four pressures
that determine the net filtration pressure (NFP)?
NFP (BHP IFOP) (BCOP IFHP) 10 mmHg
net filtration - 9 mmHg net reabsorption
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EXCHANGE OF WATER ACROSS CELL MEMBRANES
Based on osmosis Different ionic compositions in
the compartments Net flow zero Na and K have
the greatest effects
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ACID-BASE BALANCE
Normal body fluid pH 7.35 7.45 Range
maintained by three mechanisms
buffer systems strong acids converted to weaker
ones
bicarbonate system CO2 H2O H2CO3
H HCO3- phosphate system H2PO4-
HPO4-- H protein system -COOH -COO-
H -NH2 H
-NH3
exhalation of carbon dioxide (respiratory
compensation)
effects of hyperventilation effects of
hypoventilation
kidney excretion of hydrogen ions (renal
compensation)
most permanent because H are directly eliminated
from the body
Metabolic acidosis vs. respiratory
acidosis Metabolic alkalosis vs. respiratory
alkalosis
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