Body fluids compositions, and their measurements

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Body fluids compositions, and their measurements

• By DR QAZI IMTIAZ RASOOL

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OBJECTIVES

• a)Discuss the distribution of total body H2O
  (TWB) in the body
• b) List the ionic composition of different body
  compartments
•  
• c) Explain the principles of measurements
•  

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Body as an open sytemBody exchanges materials
and energywith its surroundings
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Route Range (l/day) Regulatory influences
Insensible - lungs 0.3-0.4 Atmospheric vapor pressure (temperature)
Insensible - skin 0.35-0.4 10x increase in burn victims
Sweat 0.1-2 (per hour) Temperature, exercise
Feces 0.1-0.2 Diarrheal disease
Urine 0.5-1.4-20 Body fluid composition
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FACTORS AFFECTING

• Total Body H2O
• varies depending on body fat
• Infant 73-80
• Male adult 60
• Female adult 40-50
• Effects of obesity
• Old age 45
• Climate Level of physical activity

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PERCENTAGE OF H2O IN TISSUES
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FLUID COMPARTMENTS

• EXTRA CELLUAR
  INTRA CELLULAR
• FLUID
  (cytosol)FLUID
• PLASMA INTERSTITIAL
  TRANSCELLULAR
• FLUID
  FLUID
• CSF
• Intra ocular
• Pleural
• Peritoneal
• Synovial
• Digestive Secretions

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PERCENTAGE OF WATER IN TISSUES
Average 70 kg person total
body weight 42 litres total H2O
60 28 l. Intracellular fluid
(ICF) 40 14 l.
Extracellular fluid (ECF) 20 is
important in fluid therapy divided into ¾ ISF
and ¼ plasma water 10.5 l. Interstitial fluid
(ISF) 15 3.5 l. Plasma water
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Regulation of H2O Intake

• The hypothalamic thirst center is stimulated
• By a decline in plasma volume of 1015
• By increases in plasma osmolality of 12
• Via baroreceptor input, angiotensin II, and other
  stimuli

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Net Osmotic Force Development

• Semipermeable membrane
• Movement some solute obstructed
• H2O (solvent) crosses freely
• End point
• H2O moves until solute concentration on both
  sides of the membrane is equal
• OR, an opposing force prevents further movement

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Solutes dissolved particles

• Electrolytes charged particles
• Cations positively charged ions
• Na, K , Ca, H
• Anions negatively charged ions
• Cl-, HCO3- , PO43-
• Non-electrolytes - Uncharged
• Proteins, urea, glucose, O2, CO2

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APPROXIMATE IONIC COMPOSITION OF THE BODY H2O
COMPARTMENTS
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Summary of Ionic composition
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Intra-ECF H2O RedistributionPlasma vs.
Interstitium

• Balance of Starling Forces acting across the
  capillary membrane
• osmotic forces
• hydrostatic forces
• Plasma vs Interstitial Space
• -Balance between Hydrostatic and Colloid Osmotic
  forces across the capillary membranes
• Intracellular vs Extracellular
• Osmotic effect (e.g. electrolytes)
• ICFV is NOT altered by iso-osmotic changes in
  extracellular fluid volume.

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Plasma Osmolarity Measures ECF Osmolarity

• Plasma is clinically accessible
• Dominated by Na and the associated anions
• Under normal conditions, ECF osmolarity can be
  roughly estimated as POSM 2 Nap 270-290
  mOSM

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Net Osmotic Force Development
Ionic composition very different -Total ionic
concentration very similar -Total osmotic
concentrations virtually identical

• Semipermeable membrane.
• Movement some solute obstructed.
• H2O (solvent) crosses freely.
• End point
• H2O moves until solute concentration on both
  sides of the membrane is equal.
• OR, an opposing force prevents further movement.

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Disorders of H2O Balance Dehydration
Cells lose H2O to ECF by osmosis cells shrink
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ECF osmotic pressure rises
Excessive loss of H2O from ECF
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(a) Mechanism of dehydration
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Primary Disturbance

• ECF Osmolarity ?

• ECF Osmolarity ?

1. H2O moves out of cells
2. ICF Volume decreases (Cells shrink)
3. ICF Osmolarity increases
4. Total body osmolarity remains higher than normal

1. H2O moves into the cells
2. ICF Volume increases (Cells swell)
3. ICF Osmolarity decreases
4. Total body osmolarity remains lower than normal

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CRITERIA FOR A SUITABEL DYE.

• BODY FLUID MARKER
• Must mix evenly throughout the compartment
• Non toxic, no physiological activity
• Even mixing
• Must have no effect of its own on the
  distribution of H2O or other substances in the
  body
• Either it must be unchanged during the experiment
  or if it changes , the amount changed must be
  known.
• The material should be relatively easy to measure.

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DILUTION PRINCIPLE
Principle of mass conservation Based on using a
marker whose concentration can be measured.

• Inject x gm of marker into compartment
• measure concentration at equilibrium (y gm/L)
• Since concentration mass/ volume
• Volume mass / concentration x/y L

C1V1C2V2
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Measuring Compartment Size Indirect METHOD
INDICATOR (DYE) DILUTION TECHNIQUE(Law of Mass
Conservation)
Based on concentration in a well-mixed substance
that distributes itself only in the compartment
of interest.
Volume (V)
Tracer Concentration (C)
Concentration Amount
Injected Volume of Distribution Amount of
Tracer Remained in Compartment A -
E Compartment Volume (A E)/C
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Indicators used for measuring plasma volume, ECF
volume and total body H2O
Compartment Criterion Indicators
Plasma Substance should not cross capillaries Evans blue dye radioiodinated fibrinogen radioiodinated albumin
ECF volume Substance should cross capillaries but not cross cell membranes Isotonic solutions of sucrose, inulin, mannitol, NaCl
Total body H2O (TBW) Substance distributes evenly in ICF ECF Heavy H2O, tritiated H2O, aminopyrine, antipyrine
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Total Body H2O (TBW)

• Deuterated H2O (D2O)
• Tritiated H2O (THO)
• Antipyrine

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• Blood volume /Markers used
• Obtained from plasma volume and hematocrit
• Total blood volume Plasma volume/1- Hematocrit
• Example If the plasma volume is 4 liters and the
  hematocrit is 0.45, total blood volume is ?
• PLASME VOL X 100
• 100 -HCT
• 1.T-1824 (Evans blue dye) attaches to plasma
  proteins and is removed by the liver. Measures
  plasma volume
• 2. Radioactive labeled 125 i albumin
• 3. Cr51 (radioactive chromium) is
  incubated with red blood cells then injected
• Measures total blood volume

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Take this problem

• 100 mg of sucrose is injected into a 70 kg man.
  The plasma sucrose level after mixing is 0.01
  mg/ml. If 5 mg has been metabolized during this
  period, then, what is the ECF volume?
• 9.5 L
• 14 L
• 17.5 L
• 10 L

If 1mL of solution (10mg/mL) of dye is dispersed
in chamber B and final concentration is the
chamber is 0.01mg/mL. What is the volume in
chamber B? 1000ml or 1L
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Compartments with no Compartment-Specific
Substance

1. Determine by subtraction
2. How would you measure ICF volume?
3. Cannot be measured it is calculated
   (estimated)..
4. ICF volume Total body H2O ECF volume
5. Interstitial volume
6. Can not be measured directly
7. Interstitial Fluid Volume (ISFV). ISFV
   ECFV - PV

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Measurement of other spaces

• Extracellular volume
• Na24
• Cl35
• Inulin
• Sucrose
• Mannitol
• Sulfate
• I125 iothalamate
• Disperse in plasma and interstitial fluid, but
  not permeable to cell membrane
• 30-60 min for dispersion to extracellular fluid

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Determining body fat

• Technique bioelectric impedance technique
• Principle
• Body fluids conduct electricity well
• But fat is anhydrous and therefore is a poor
  conductor of electricity
• The resistance to flow of a small current between
  points on the body is proportional to fat mass.

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Lean body mass (LBM)

• Definition LBM is fat free mass
• Total body mass fat mass fat free mass
• Note fat is relatively anhydrous
• Note the H2O content of LBM is constant
• H2O content of LBM is constant - 70 ml /100 g
  tissue

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Take this problem

• In a healthy adult male weighing 70 kg, total
  body H2O (TBW) was measured to be 42 L. What is
  his lean body mass (LBM)? What is his fat mass?
• Given TBW 42 L
• Assume all this H2O is in LBM that fat is H2O
  free
• We know that H2O content of LBM is 70 ml/100 g
• Thus, if TBW is 42 L, LBM 60 kg
• Since he weights 70 kg, his fat mass is 70-60
  10 kg

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