Body Fluid Compartments

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Body Fluid Compartments Part 1Body
Composition

• E.S.Prakash,
• Faculty of Medicine, AIMST University
• E-mail dresprakash_at_gmail.com

Note to Readers This is one of the lectures in
the Molecular Cellular Basis of Medicine
course, Element 2 General Physiology, Nerve
Muscle Physiology, Basics of Hematology in Term
1 of Year 1 of the MBBS programme.
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Plasma about 1/4th of ECF volume
ECF
Interstitial Fluid ISF About 3/4th of ECF
volume
Intracellular Fluid ICF 2/3 of total body
water is inside cells
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Body fluid volumes in a healthy 70-kg adult male
Compartment Volume Subdivisions
Intracellular fluid, ICF (2/3 of TBW) 28 L -
Extracellular fluid, ECF (Sucrose space) 1/3 of TBW 14 L 10.5 L (Interstitial fluid)
Extracellular fluid, ECF (Sucrose space) 1/3 of TBW 14 L 3.5 L (Plasma)
Total body water (TBW) 60 of body weight 42 L -
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Measuring body fluid volumes

• Principle Indicator-dilution principle
• Method
• Administer a known amount (A) of a substance that
  will get distributed in a particular body fluid
  compartment
• Determine the final steady state concentration
  (C) of this indicator in blood
• Volume of distribution Vd of the indicator
  Amount of indicator injected (A)
• Concentration in blood after mixing (C)

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Indicators used for measuring plasma volume, ECF
volume and total body water
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 water (TBW) Substance distributes evenly in ICF ECF Heavy water, tritiated water, aminopyrine, antipyrine
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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

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Solution

• Amount of sucrose injected 100 mg
• Amount metabolized 5 mg
• Amount remaining in ECF (A) 95 mg
• Concentration in plasma after mixing (C) 0.01
  mg/ml
• Thus, volume of distribution (Vd) of sucrose
• A / C 95 mg / 0.01 mg/ml
• 9500 ml 9.5 L ( ECF volume)

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• How would you measure interstitial fluid (ISF)
  volume?
• Cannot be measured it is calculated
  (estimated)..
• ISF volume ECF volume plasma volume
• How would you measure ICF volume?
• Cannot be measured it is calculated
  (estimated)..
• ICF volume Total body water ECF volume

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Transcellular fluids

• Cerebrospinal fluid
• Synovial fluid
• Aqueous humor
• Pleural fluid
• Peritoneal fluid
• In health, the total volume of transcellular
  fluids is lt 1 L.

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What is the relationship between blood volume and
plasma volume?

• Blood plasma cells in blood
• Volume of cells packed cell volume (PCV)
• PCV is also called hematocrit (Hct)
• Blood volume
• plasma volume 100 / (100 Hct)

Image from http//users.rcn.com/jkimball.ma.ultran
et/BiologyPages/B/Blood.html
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Blood volume plasma volume (100/100-Hct)

• In a healthy 70 kg adult male, plasma volume
  (measured using the Evans Blue dye) was found to
  be 3000 ml. Hematocrit was 40. Calculate his
  blood volume.
• 5000 ml
• 5200 ml
• 5400 ml
• 5600 ml

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Measuring red cell volumeNote measuring is
different from calculating something

• Technique principle
• Use Chromium 51 labeled RBC as the indicator
• Inject a known amount of Cr 51 labeled RBC
  intravenously
• Allow them to mix with RBC in blood
• Measure the fraction of RBC tagged with Cr 51
• Principle same indicator dilution principle.

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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 water content of LBM is constant
• Water 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 water (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 water is in LBM that fat is
  water free
• We know that water 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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Body composition Lean body mass fat free mass
Total body weight fat-free mass fat mass
Tom Jerry
Body mass 100 kg 100 kg
Fat mass 15 15 kg 30 30 kg
Lean body mass 85 85 kg 70 70 kg
Overall health Fit Obese
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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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Now you should be able to answer these questions

1. Classify body fluid compartments. Mention the
   volumes of body fluid compartments in a healthy
   adult male weighing 70 kg.
2. Explain the principle that is used in the
   measurement of body fluid volumes and RBC volume.
   
3. Mention the indicator that is used to measure the
   volume of plasma, ECF, and total body water and
   explain why these indicators are chosen for
   measuring them.
4. How you would measure interstitial fluid volume?
5. How you would measure ICF volume?

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1. Mention the relationship between hematocrit and
   blood volume.
2. Describe the meaning of the term lean body
   mass.
3. Mention the relationship between lean body mass
   and total body mass.
4. Briefly explain the principle that is used in the
   estimation of body fat.
5. Briefly explain gender differences in body
   composition.

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Required Reading

• Ganong WF. Chapter 1. The General and Cellular
  Basis of Medical Physiology. In Review of
  Medical Physiology. Intl ed, Mc Graw Hill, 2005
  pages 1-6.