Body Fluid Compartments and Fluid Balance
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Transcript of Body Fluid Compartments and Fluid Balance
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Body Fluid Compartments
and
Fluid Balance
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Water gain must = water loss
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Rate of formation of metabolic water is not regulated
Source of metabolicallyformed water
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Osmolarity of plasma is about 300 mOsm/L
(Measured by a method called “Freezing Point Depression)
TONICITY is Osmolarity in relation to that of plasma. It has the ability to change the VOLUME of a cell
Isotonic solution: same osmolarity as of plasma
Hypertonic solution
Hypotonic solution?
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ECF IS ISOTONICOsmotic equilibrium is maintained rapidly between ICF and ECF
Isotonic fluid gain: e.g Intravenous infusion of isotonic saline (0.9 % NaCl, 5% glucose solution)
Isotonic fluid loss: Hemorrhage No net fluid shift occur
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ECF IS HYPOTONICWhat happens?
Water moves into the cells from ECF until osmotic equilibrium is achieved. Pronounced swelling of neurons leads to brain dysfunction
Swelling of muscle leads to muscle weakness.Hypertension and edema caused by expansion of plasma volume.
What Causes this?Over hydration:
Renal failure with inability
to excrete diluted urine
Excessive drinking (transient)
Increase in ADH secretion
Water intoxication:
condition of over hydration,
hypotonicity and cellular swelling
from excess water.
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ECF IS HYPERTONICWhat happens?
Water moves out of the cells to ECF until osmotic equilibrium is achieved Cells shrink as water leaves them
Neurons dehydration causes disturbances in brain function manifested as mental confusion to coma.
What Causes this?Dehydration due to: Insufficient
water intake Excessive
water loss (vomiting or
diarrhea) Diabetes
Insipidus (deficiency of
ADH)
Accumulation of high levels of osmotically active solutes (urea in kidney
failure)
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Tonicity & RBC
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Regulation of body water gain
Rate of formation of
metabolicwater is not regulated to
maintain homeostasis
Water gain is regulated mainly
by drinking through thirst
mechanism2% decrease in body mass due
to fluid loss causes mild dehydration
Baroreceptor
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27_table_01
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Measurement of fluid volumes in the different body
compartmentsDye-dilution metod (Indicator-dilution)
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Measurements of various body volumes
Total body wateruse of a substance which when inserted in to the blood, will spread evenly through out all the body compartments.
Substances used i. Radio active water ii. Antipyrine –because it is lipid
soluble
Extra cellular volume Substance should disperse easily through water/plasma but NOT enter cells
Substances used I Radioactive Na, Inulin These rapidly spread through out extra cellular space30-60
min Extra cellular volume is also called SODIUM space or INULIN
space
ICF = TBW-Extra cellular volume
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Plasma & blood volumes Plasma Volume Substance must stay INSIDE blood
compartment after it is injected in to the blood stream
Evans Blue (Dye) is the best choice
Blood volume = Plasma volume + hematocrit (cell volume)
Then BV = Plasma Volume/ (1-
Hct)
Given Plasma vol as 3 litres, and
Hct as 0.45 BV = 3/(1-0.45) = 3/0.55 = 5.45 L
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Measurement of various body fluid compartments
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Summary 1. Osmolarity, its normal value, and osmotic pressure
2. Hydrostatic pressure
3. Distribution of body water
4. Intra and extra cellular fluids and their composition
5. Tonicity of plasma and learnt what is iso, hypo and hyper tonicity
6. Measurements of body fluid compartments