Body fluids

Dept. of physiology AUADr. R. Sanii

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Physiology of Body fluids

•1. Body fluids compartments

•2. Volumes and ionic composition of each compartment

•3. Osmolarity, and concentration of Na+, K+ , Cl+, Hco3-, Protein, Creatinine and Urea

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Objectives 4. Measurements of Plasma, blood

volume, extracellular volume, intracellular volume, and total body volume

5. Driving force responsible for the movements of water across cell and capillary membrane.

6. How extracellular and intracellular volumes changes under pathological conditions such as edema, dehydration, and volume depletion

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Daily Water Input and Output

• Intake

•A. pure water 1400 ml

•B. content of food 700 ml

•C. Chemically produced 200 ml

•Output

• Lost in Urine 1400 ml

• Lost in feces 100 ml

•Skin (insensible) 300 ml

• d. Lungs (insensible) 100 ml

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2300

2300

Body Water Spaces

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Transcellular water = water in bladder, GI tract, eyeballs, gall bladder, etc.

for a lean, 70 kg male

Composition Of body fluids

Is there a difference between

ICF &ECF

Composition?

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  Plasma Interstitial Intracellular

Sodium 

Chloride 

Potassium 

Bicarbonate 

Protein 

135-145 mM 

95-110 mM 

3-5 mM 

22-28 mM 

7g %

135-145 mM 

95-110 mM 

3-5 mM 

22-28 mM 

0 g%

14 mM 

10mM 

120145 mM 

Low 

A Major anion

Units of measurements

1. Mass per volume

Example: Gram per litter, Mg per litter, Mg /deciliter)

2. Molarity ( the amount relative to its molecular weight)

Example: since Mw of glucose is 180 if we dissolve 180 g of glucose in one litter the concentration will be one mole per litter.

3. Equivalence

Example: NaCl, Since NaCl will dissociate in to Na and Cl then the solution will contains one mole of each. Since valence of both is 1 then each of then will have one eq/L

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Distribution of volume 12If: V1 = volume injected (ml), and C1 = concentrated

injected (mg/ml)

Then: weight injected = V1 x C1 (ml x mg/ml = mg)

After injection, equilibration, and ignoring excretion & metabolism:

If: V2 = body water space volume (ml), C2 = marker concentration (mg/ml)

Then: weight in body after equilibration = V2 x C2

Weight injected at start = weight in body water space after equilibration

Therefore:V1 x C1 = V2 x C2l

or: V2 (volume of distribution) = V1 x C1/ C2

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Markers for Body Water Spaces

Body water space Markers

Total body water: T2O, D2O, antipyrine

Extracellular water: inulin, mannitol, Na+

Plasma: 125I albumin, 51Cr erythrocytes, -- Evans blue (binds to albumin)

Intracellular volume = total body volume - extracellular volume

Interstitial volume = extracellular volume - plasma volume

Calculation of osmolality

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• Osmolality depends on the number of particles, not the nature of those particles

• i.e. 1 albumin (M.Wt. 67,000) = 1 Na+ (M.Wt. 23)

• plasma (osmolality ~285 mOsm/kg water) has ~7 g/dL protein, but the protein osmolality is ~ 1.5 mOsm/kg water

• Assuming complete dissociation:

• “D5W” (5% w/v glucose) = 300 mM = 300 mOsm/kg water

• 150 mM NaCl = 150 mM Na+ + 150 mM Cl- = 300 mOsm/kg water

• 20 mM CaCl2 = 20 mM Ca++ + 2 x 20 mM Cl- = 60 mOsm/kg water

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Water or D5W (isotonic glucose) on body water spaces

Intravenous D5W: after metabolism of glucose to glycogen, D5W is osmotically equivalent to drinking water

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Water or D5W (Dannett-Yarrow diagram)

1. Horizontal axis: volume2. Vertical axis: osmolality3. Solid lines: normal4. Dashed line: after v5. ECF: extracellular fluid6. ICF: intracellular fluid

Isotonic saline or Lactate/Ringer on body water spaces

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Hypertonic saline on body water spaces

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Hypertonic saline on body water spaces

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Sweating without fluid replacement on body water spaces

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Sweating without fluid replacement (Dannett-Yarrow)

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?

Distribution of fluid between interstitial & vascular spaces

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Controlled by “Starling forces”where: Pc = hydrostatic pressure of capillary (blood pressure)

Πc = protein osmotic (oncotic) pressure of capillary

PIF = hydrostatic pressure of interstitial fluid. ΠIF = protein osmotic pressure of interstitial fluid

then: net pressure for efflux = (Pc - PIF) - (Πc-ΠIF)

Plasma or whole blood on body water spaces

Isotonic saline:

lowers plasma oncotic pressure, raises blood pressure

therefore saline distributes throughout extracellular space

Plasma or whole blood:

maintains plasma oncotic pressure, raises blood pressure

most fluid remains in vascular space

Edema formation

Definition: pathological increase in the volume of the interstitial fluid space

Usually caused by disruption of Starling forces • ↓Πc plasma protein osmotic pressure

(e.g. liver disease, nephrotic syndrome)• ↑ ΠIF 2° to ↑capillary protein permeability

(e.g. burns, trauma, infection)• ↑ Pc capillary pressure

(e.g. left heart failure, 1° renal salt & water retention, cirrhosis)• blockage of lymph flow

(e.g. filariasis, lymph node removal)

Edema: decreased πc (plasma protein osmotic pressure)

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Causes:

nephrotic syndrome: urinary protein loss > liver replacement (~3.5 g/day)liver disease (impaired synthesis of albumin)

Edema: increased πi (interstitial protein osmotic

pressure)30

Cause: increased protein permeability of capillary endothelium →↑πi

Contributing factors: vasodilatation →↑capillary b.p., →↑filtration area

Edema increased Pc (capillary blood pressure)

Example: heart failure

Edema: increased Pc (capillary blood pressure)

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Primary cause:

salt & water retention →vascular volume overload

Thank you