Cell Water Balance
Terms
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- Major fluid compartments
-
1) intracellular
2) extracellular
3) interstitial
4) blood plasma - Major intracellular ion
- K
- Major extracellular ion
- Na
- osmolarity of body fluid compartments
- 290 mosmoles/L
- intracellular fluid compartment
-
25 L
2/3 of total body water - extracellular fluid compartment
-
16 L
1/3 of total body water - interstitial fluid compartment
-
13 L
3/4 of ECF (1/4 of TBW) - blood plasma fluid compartment
-
1) blood volume = plasma volume + RBC volume (5L) (1/4 of ECF)
2) hematocrit: % of blood volume occupied by RBC
- RBC volume/ blood volume * 100
plama volume/blood volume = 1 - Hct - Barriers separating compartments
-
1) Cell membrane
2) Capillary Endothelial layer - Cell membrane
-
- Na-K pump maintains high [K] and low [Na} inside cell
- Na impermeabl to CM without channels, so [Na] determines osmolarity - Capillary Endothelial Layer
-
- permeable to all molecules but large ones
- albumin = osmotic effect on water
- water forced out by blood pressure - Total Body Water
-
measured by:
1) 3H20
2) antipyrine - Extracellular Fluid
-
1) 22Na
2) inulin
3) mannitol - Plasma volume
-
1) 131I-Albumin
2) Evans blue - Intracellular Volume
- TBW - ECF
- Interstitial Volume
- ECF - Plasma Volume
- water lost in exhalation
- 350 ml/day
- water lost from kidneys
- 500 ml/day
- evaporative water loss
- 550 ml/day
- normal ingestion of water
- 2L
- 60-40-20 rule
-
60% of body weight = water
40% = IC 2/3 of TBW
20% = EC - Volume Contraction
-
1) Diarrhea
2) dehydration
3) adrenal insufficiency - Volume Expansion
-
1) Infusion of isotonic NaCl
2) eating salt
3) - isosmotic volume contraction
-
ex. diarrhea
Increase:Hcrit, Plasma protein
Decrease:ECF volume
No change:osmolarity, ICF volume - Hyperosmotic Volume Contraction
-
ex. sweating, fever, diabetes I
Increase:osmolarity, plasma protein
Decrease: ECF volume, ICF volume,
No change: Hcrit - Hyposmotic volume contraction
-
ex. adrenal isuffciency
Increase: ICF volume, Hcrit, plasma protein
Decrease:ECF volume, osmolarity
No change: - Isosmotic volume expansion
-
ex.infusion of isotonic NaCl
Increase:ECF volume,
Decrease:Hcrit, plasma protein
No change: ICF volume, osmolarity - Hyperosmotic volume expansion
-
ex. Salt intake
Increase:ECF volume,
Decrease: ICF volume, Hcrit, plasma protein
No change: - Hyposmotic volume expansion
-
ex. Syndrome of inapproriate ADH
Increase:ECF volume, ICF volume,
Decrease: osmolarity, plasma protein
No change: Hcrit