Body Fluid Compartments – Part 1Body Fluid Compartments – Part 1Body Composition Body Composition

E.S.Prakash, E.S.Prakash,

Faculty of Medicine, AIMST UniversityFaculty of Medicine, AIMST University

E-mail: E-mail: dresprakash@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.

Intracellular Fluid [ICF]; 2/3 of total body water is inside cells

Interstitial Fluid [ISF]; About 3/4th of ECF volume

Plasma [about 1/4th of ECF volume]

ECF

Body fluid volumes in a Body fluid volumes in a healthy 70-kg adult malehealthy 70-kg adult male

CompartmentCompartment VolumeVolume SubdivisionsSubdivisions

Intracellular fluid, ICF (2/3 Intracellular fluid, ICF (2/3 of TBW)of TBW)

28 L28 L --

Extracellular fluid, ECFExtracellular fluid, ECF

(Sucrose space); (Sucrose space);

1/3 of TBW1/3 of TBW

14 L14 L 10.5 L10.5 L

(Interstitial fluid)(Interstitial fluid)

3.5 L3.5 L

(Plasma)(Plasma)

Total body water (TBW); Total body water (TBW);

60% of body weight60% of body weight

42 L42 L --

Measuring body fluid volumes:Measuring body fluid volumes:

Principle:Principle: Indicator-dilution principle Indicator-dilution principle

Method:Method:

1.1. Administer a known amount (A) of a substance that will Administer a known amount (A) of a substance that will

get distributed in a particular body fluid compartment;get distributed in a particular body fluid compartment;

2.2. Determine the final steady state concentration (C) of this Determine the final steady state concentration (C) of this

indicator in blood;indicator in blood;

3.3. Volume of distribution Vd of the indicator = Volume of distribution Vd of the indicator =

Amount of indicator injected (A) Amount of indicator injected (A)

Concentration in blood after mixing Concentration in blood after mixing

(C)(C)

Indicators used for measuring plasma volume, Indicators used for measuring plasma volume, ECF volume and total body waterECF volume and total body water

CompartmentCompartment CriterionCriterion IndicatorsIndicators

PlasmaPlasma Substance should Substance should not cross not cross capillariescapillaries

Evans blue dye; Evans blue dye;

radioiodinated fibrinogen; radioiodinated fibrinogen;

radioiodinated albuminradioiodinated albumin

ECF volumeECF volume Substance should Substance should cross capillaries cross capillaries but not cross cell but not cross cell membranesmembranes

Isotonic solutions of Isotonic solutions of sucrose, inulin, mannitol, sucrose, inulin, mannitol, NaClNaCl

Total body Total body water (TBW)water (TBW)

Substance Substance distributes evenly distributes evenly in ICF & ECFin ICF & ECF

Heavy water, tritiated water, Heavy water, tritiated water, aminopyrine, antipyrineaminopyrine, antipyrine

Take this problem:Take this problem:

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

A.A. 9.5 L9.5 L

B.B. 14 L14 L

C.C. 17.5 L17.5 L

D.D. 10 L10 L

Solution:Solution:

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

= A / C = 95 mg / 0.01 mg/ml = A / C = 95 mg / 0.01 mg/ml

= 9500 ml = 9.5 L (= ECF volume)= 9500 ml = 9.5 L (= ECF volume)

How would you measure interstitial fluid (ISF) volume?How would you measure interstitial fluid (ISF) volume? Cannot be measured; it is calculated (estimated)..Cannot be measured; it is calculated (estimated).. ISF volume = ECF volume – plasma volumeISF volume = ECF volume – plasma volume

How would you measure ICF volume?How would you measure ICF volume? Cannot be measured; it is calculated (estimated)..Cannot be measured; it is calculated (estimated).. ICF volume = Total body water – ECF volumeICF volume = Total body water – ECF volume

Transcellular fluidsTranscellular fluids

Cerebrospinal fluidCerebrospinal fluid Synovial fluidSynovial fluid Aqueous humorAqueous humor Pleural fluidPleural fluid Peritoneal fluidPeritoneal fluid

In health, the total volume of transcellular fluids is < In health, the total volume of transcellular fluids is < 1 L.1 L.

What is the relationship between blood What is the relationship between blood volume and plasma volume?volume and plasma volume?

Blood = plasma + cells in bloodBlood = plasma + cells in blood

Volume of cells: packed cell volume Volume of cells: packed cell volume (PCV)(PCV)

PCV is also called hematocrit (Hct)PCV is also called hematocrit (Hct)

Blood volume Blood volume

= plasma volume × 100 / (100 – Hct)= plasma volume × 100 / (100 – Hct)Image from http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/B/Blood.html

Blood volume = plasma volume Blood volume = plasma volume × (100/100-Hct)× (100/100-Hct)

In a healthy 70 kg adult male, plasma In a healthy 70 kg adult male, plasma volume (measured using the Evans Blue dye) volume (measured using the Evans Blue dye) was found to be 3000 ml. Hematocrit was was found to be 3000 ml. Hematocrit was 40%. 40%. CalculateCalculate his blood volume. his blood volume.

A.A. 5000 ml5000 ml

B.B. 5200 ml5200 ml

C.C. 5400 ml5400 ml

D.D. 5600 ml5600 ml

MeasuringMeasuring red cell volume red cell volumeNote: measuring is different from calculating somethingNote: measuring is different from calculating something

Technique & principle:Technique & principle:Use Chromium 51 labeled RBC as the indicator; Use Chromium 51 labeled RBC as the indicator; Inject a known amount of Cr 51 labeled RBC Inject a known amount of Cr 51 labeled RBC

intravenously;intravenously;Allow them to mix with RBC in blood; Allow them to mix with RBC in blood; Measure the fraction of RBC tagged with Cr 51;Measure the fraction of RBC tagged with Cr 51;Principle:Principle: same – indicator dilution principle. same – indicator dilution principle.

Lean body mass (LBM)Lean body mass (LBM)

Definition:Definition: LBM is fat free mass LBM is fat free mass Total body mass = fat mass + fat free massTotal body mass = fat mass + fat free mass Note:Note: fat is relatively anhydrous fat is relatively anhydrous Note:Note: the water content of LBM is constant the water content of LBM is constant Water content of LBM is constant - 70 ml /100 g tissueWater content of LBM is constant - 70 ml /100 g tissue

Take this problem:Take this problem:

In a healthy adult male weighing 70 kg, total body In a healthy adult male weighing 70 kg, total body water (TBW) was measured to be 42 L. What is his water (TBW) was measured to be 42 L. What is his lean body mass (LBM)? What is his fat mass? lean body mass (LBM)? What is his fat mass? Given TBW = 42 LGiven TBW = 42 LAssume all this water is in LBM & that fat is water freeAssume all this water is in LBM & that fat is water freeWe know that water content of LBM is 70 ml/100 gWe know that water content of LBM is 70 ml/100 gThus, if TBW is 42 L, LBM = 60 kgThus, if TBW is 42 L, LBM = 60 kgSince he weights 70 kg, his fat mass is 70-60 = 10 kgSince he weights 70 kg, his fat mass is 70-60 = 10 kg

Body compositionBody composition Lean body mass = fat free mass Lean body mass = fat free mass

Total body weight = fat-free mass + fat massTotal body weight = fat-free mass + fat mass

TomTom JerryJerry

Body massBody mass 100 kg 100 kg 100 kg100 kg

Fat mass Fat mass 15 % = 15 kg15 % = 15 kg 30 % = 30 kg30 % = 30 kg

Lean body mass Lean body mass 85 % = 85 kg85 % = 85 kg 70 % = 70 kg70 % = 70 kg

Overall health Overall health Fit Fit ObeseObese

Determining body fat:Determining body fat:

Technique:Technique: bioelectric impedance technique bioelectric impedance techniquePrinciple:Principle:

Body fluids conduct electricity well;Body fluids conduct electricity well;But fat is anhydrous and therefore is a poor But fat is anhydrous and therefore is a poor

conductor of electricity;conductor of electricity;The resistance to flow of a small current between The resistance to flow of a small current between

points on the body is proportional to fat mass.points on the body is proportional to fat mass.

Now you should be able to answer these Now you should be able to answer these questions:questions:

1.1. Classify body fluid compartments. Mention the volumes Classify body fluid compartments. Mention the volumes of body fluid compartments in a healthy adult male of body fluid compartments in a healthy adult male weighing 70 kg. weighing 70 kg.

2.2. Explain the principle that is used in the measurement of Explain the principle that is used in the measurement of body fluid volumes and RBC volume. body fluid volumes and RBC volume.

3.3. Mention the indicator that is used to measure the volume Mention the indicator that is used to measure the volume of plasma, ECF, and total body water and explain why of plasma, ECF, and total body water and explain why these indicators are chosen for measuring them.these indicators are chosen for measuring them.

4.4. How you would measure interstitial fluid volume?How you would measure interstitial fluid volume?

5.5. How you would measure ICF volume?How you would measure ICF volume?

6.6. Mention the relationship between hematocrit and blood Mention the relationship between hematocrit and blood volume.volume.

7.7. Describe the meaning of the term ‘lean body mass’. Describe the meaning of the term ‘lean body mass’.

8.8. Mention the relationship between lean body mass and Mention the relationship between lean body mass and total body mass.total body mass.

9.9. Briefly explain the principle that is used in the Briefly explain the principle that is used in the estimation of body fat.estimation of body fat.

10.10. Briefly explain gender differences in body composition.Briefly explain gender differences in body composition.

Required Reading:Required Reading:

Ganong WF. Chapter 1. The General and Cellular Basis Ganong WF. Chapter 1. The General and Cellular Basis

of Medical Physiology. In: of Medical Physiology. In: Review of Medical Review of Medical

Physiology.Physiology. Int’l ed, Mc Graw Hill, 2005; pages 1-6. Int’l ed, Mc Graw Hill, 2005; pages 1-6.