Water & The Body Fluids
• 60% of adult body weight
-Water makes up ¾ of the
weight of lean tissue
-Water makes up ¼ of the
weight of fat
Copyright 2005 Wadsworth Group, a division of Thomson Learning
Water & Body Fluids
• Functions of water:
–Transport
–Structural support for molecules
–Participates in metabolic reactions
–Solvent
–Lubricant & shock absorber
–Body temperature regulation
–Maintains blood volume & blood
pressure
Water & The Body Fluids
• Water balance
–Intracellular fluid-within the cells
–Extracellular fluid-outside the cells
•Interstitial fluid
•Plasma
Copyright 2005 Wadsworth Group, a division of Thomson Learning
One Cell
And Its
Associated
Fluids
Copyright 2005 Wadsworth Group, a division of Thomson Learning
Water & Body Fluids
•
Water Balance
-Intake/output = 2.5 liters/day
-Regulated by hypothalamus & kidneys
-Carefully controlled by:
1. Intake (liquid, foods, metabolic water)
affected by thirst & satiety
2. Output (losses via kidneys, skin, lungs,
feces) affected by blood salts, volume &
blood pressure
How The Body Regulates Blood Volume
Copyright 2005 Wadsworth Group, a division of Thomson Learning
Copyright 2005 Wadsworth Group, a division of Thomson Learning
Water & Body Fluids
• Recommendations:
-Needs vary according to type of food
eaten, temperature, humidity, activity
level, etc.
-General rule: 1–1.5 ml/kcal expended
Example: if 2000 kcal “burned” then
2-3 liters suggested; >8 cups from fluids
and the rest comes from food &
metabolic water
-Urine should be pale yellow
-Caffeine & alcohol act as diuretics so not
good water substitutes
Fluid & Electrolyte Balance
• Electrolytes – salts that dissolve in
water, forming ions
• Dissociation of salt in water
–Ions
•Cations- + charged particles
•Anions- - charged particles
–Electrolyte solution
Copyright 2005 Wadsworth Group, a division of Thomson Learning
Water Dissolves Salts
And Follows Electrolytes
Copyright 2005 Wadsworth Group, a division of Thomson Learning
Fluid & Electrolyte Balance
• Electrolytes attract water - affects fluid
distribution in the body by osmosis
• Water follows electrolytes
– Solutes
– Osmosis
– Osmotic pressure
• Electrolyte concentration regulated by
kidneys
• Electrolytes & proteins act as buffers to
maintain the pH of body fluids – acid/base
balance
Copyright 2005 Wadsworth Group, a division of Thomson Learning
Copyright 2005 Wadsworth Group, a division of Thomson Learning
Acid-Base Balance
• pH
• Regulation by the buffers
–Bicarbonate
–Carbonic acid
• Regulation by the kidneys
• Regulation by the lungs
Copyright 2005 Wadsworth Group, a division of Thomson Learning
Copyright 2005 Wadsworth Group, a division of Thomson Learning
Fluid & Electrolyte Imbalance
• Replacing lost
fluids and
electrolytes
–Oral rehydration
therapy (ORT)a simple
solution of
sugar, salt and
water
Copyright 2005 Wadsworth Group, a division of Thomson Learning
Fluid & Electrolyte Imbalance
• Sodium and chloride most easily lost
• Different solutes lost by different
routes
• Rapid fluid/electrolyte loss, i.e.
vomiting, diarrhea, heavy sweating,
fever, burns, wounds = medical
emergency
Copyright 2005 Wadsworth Group, a division of Thomson Learning