This document summarizes the composition and distribution of body fluids in the human body. It discusses that the normal adult body is composed of 60% water, 7% minerals, 18% protein, and 15% fat. Total body water is distributed between intracellular fluid (ICF, 40% of body weight) and extracellular fluid (ECF, 20% of body weight). ECF is further divided into plasma (5% of body weight), interstitial fluid (15% of body weight), and transcellular fluid (1.5% of body weight). The document also describes the ionic composition of different body fluids and units used to measure solute concentration like moles, equivalents, and osmoles. It introduces

1. Body fluid & composition
Dr. Amruta N. Kumbhar
Assistant Professor
Dept. Of Physiology

2. Specific learning objectives
• Distribution of total body water in the body
• Ionic composition of body fluids
• Define: moles; equivalents; osmoles
• Concepts of pH; H+ concentration, Buffer system

3. Introduction
• The normal body in an average adult male is composed of water
(60%)
• minerals (7%)
• protein and related substances (18%)
• fat (15%)
• The water, denoted by the term total body water (TBW), the
electrolytes need special emphasis
• TBW 10% lower in young females
• In infants TBW is 65-75 % of body weight

4. Distribution of total body water (TBW)
Compartment Volume (L) Percent
Body weight Body water
Total body water (TBW) 42 60 100
a) Extra Cellular Fluid (ECF) 14 20 33
b) Intra cellular fluid (ICF) 28 40 67

5. Distribution of extra cellular fluid (ECF) in a
normal adult 70 kg person
compartment Volume (L) Percent ()
Body weight Body water
Plasma (25% of ECF) 3.5 4-5 8
Interstitial plus transcellular fluid
(75% of ECF)
10.5 15 25

6. ECF
1. Plasma :
100- Hematocrit (PCV)
Plasma volume (L) = blood volume(L)x
100
• comprises about 5% of the body weight (i.e. 25% of the ECF).
• On an average out of 5 L of total blood volume 3.5 L is plasma.

7. 2. Interstitial fluid
• part of the ECF i.e outside the vascular system
• It constitutes the major portion (about 3/4) of the ECF.
• The composition of interstitial fluid is the same as that of plasma
except it has little protein.
• Thus, interstitial fluid is an ultrafiltrate of plasma
• Lymph constitute 2-3% of body wt.

8. 3.Transcellular fluid
• It is the fluid contained in the secretions of the secretory cells and
cavities of the body
• e.g. saliva, sweat, cerebrospinal fluid, intraocular fluids (aqueous
humour and vitreous humour), pericardial fluid, bile, fluid present
between the layers (pleura, peritoneum and synovial membrane),
lacrimal fluid and luminal fluids of the gut, thyroid and cochlea.
• Transcellular fluid volume is relatively small,
• about 1.5% of the body weight, i.e. 15 mL/kg body weight
• about 1 L in a person of 70 kg

9. 4. Mesenchymal tissue fluid
• The mesenchymal tissues such as dense connective tissue, cartilage
and bones contain about 6% of the body water.
• The interstitial fluid, transcellular fluid and mesenchymal tissue fluid
combinedly form the 75% of ECF.
• The normal distribution of total body water in the fluid compartments
is kept constant by two opposing sets of forces: osmotic and
hydrostatic pressure.

10. Distribution of total body water in a normal 70 kg
person
Compartment Volume (L) Body weight (%) Body water (%)
Total body water
(TBW)
42 60 100
Intracellular fluid
(ICF)
28 40 67
Extracellular fluid 14 20 33

11. Intracellular fluid compartment
• The intracellular fluid (ICF) compartment comprises about 40% of the
body weight
• It is the fluid contained within the body cells
• the bulk of which is contained in the muscles

12. MEASUREMENT OF BODY FLUID VOLUMES
• The volume of water in each fluid compartment can be measured by the
indicator dilution principle
• It is based on relationship between –
A1 – A2
V =
where, C
V = Volume of fluid distributed in compartment
A1 = Amount of indicator injected in the fluid,
A2 = Amount of indicator removed by excretion and metabolism, and
C = Concentration of the indicator in the fluid.

13. Q. If 150 mg of sucrose (A1) is injected into a 70 kg man, 10 mg
sucrose (A2) has been excreted or metabolized and the concentration
of plasma sucrose (C) measured is 0.01 mg/mL; then the volume
distribution of sucrose is ?

14. Characteristics of the Indicator (marker) used
• It should be non-toxic.
• It must mix evenly throughout the compartment being measured.
• It should be relatively easy to measure its concentration.
• It must have no effect of its own on the distribution of water or other
substances in the body.
• Either it must be unchanged by the body during the mixing period or
the amount changed (excreted and/or metabolized) must be known.

15. 1. Measurement of total body water volume
• The volume of TBW can be measured by injecting a marker which will
be evenly distributed in all the compartments of body fluid. Such
markers include:
• Deuterium oxide (D2O),
• Tritium oxide, and
• Aminopyrine

16. 2. Measurement of extracellular fluid volume
1. Radioactive substances like sodium, chloride (36Cl− and 38Cl−),
bromide (82Br−), sulphate and thiosulphate; and
2. Non-metabolizable saccharides like inulin, mannitol and sucrose
• Most accurate method of measuring the volume of ECF is by using
inulin (polysaccharide, MW 5200)
• The values of ECF volume are calculated from the values of
concentration of inulin in the plasma since it makes an important
component of the ECF.

17. 3. Measurement of plasma volume
• The plasma volume can be measured by injecting those markers which bind
strongly with the plasma protein
• either do not diffuse or diffuse only in small quantities into the interstitium.
These substances are
1. Radioactive iodine – 131I, and
2. The dye Evan’s blue – T-1824.
3. radioactive isotopes of chromium (51Cr)
4. Radio iodinated human serum albumin (RISA)
5. Radio iodinated gamma globulin & fibrinogen- do not leak out of blood
stream 100 - PCV
6. plasma volume= blood volume x
100

18. 4. Measurement of intracellular fluid volume
• values of ICF volume are calculated from the values of TBW and ECF
as
• ICF volume = TBW volume − ECF volume.

19. 5. Measurement of interstitial fluid volume
• Its values can be roughly calculated from the values of ECF volume
and plasma volume as
• Interstitial fluid volume = ECF volume − plasma volume
• The ECF volume/intracellular fluid volume ratio is larger in infants and
children as compared to adults,
• but absolute volume of ECF in children is smaller than in adults
• Applied aspect-

20. Ionic composition of body fluids
• Ions constitutes approx. 95% of the solutes in the body fluids
Ionic distribution in the various body fluids (mEq/L of H2O)
ions plasma Interstitial fluid ICF
Cations
Na 153 145 12
K 5.4 5 155
Mg2+ 1.9 2 15
Others 2.7 2 2
Total cations 163 154 184

21. Ionic composition of body fluids
anions ions plasma Interstitial fluid ICF
Cl- 111 110 8
HCO3- 26.2 27 8
Phosphate 1 2 90
Proteins 17.2 15 60
Others 7.6 - 18
Total anions 163 154 184
Total ions 326 308 368

22. • Na+, ca2+ Cl-,& HCO-
3 are largely extracellular
• whereas K+, Mg2+, organic phosphates & proteins are predominantly
present in ICF
• Essentially all of the body K+ is in the exchangeable pool whereas
• Only 65- 70% of body Na+ is exchangeable
• Only the exchangeable solutes are osmotically active
• Almost all of the body Ca2+ & most of the body Mg2+ are non
exchangeable

23. Units for measuring concentration of solutes
1. Moles :
• molecular weight of the substance in grams
• Each mole consist of appx. 6 x 1023 molecules
• 1 mmol is 1/1000 of a mole
2. equivalents:
• It is the standard unit for expressing the solutes in the body which are in
the form of charged particles.
• One equivalent(Eq) is 1 mole of an ionized substance divided by its valency
• mEq is 1/1000 of 1 eq
• Normality of solution is the number of gram equivalents in 1 litr.
• 1N solution of HCL contains 1 + 35.5 gm/l = 36.5gm/L

24. 3. Osmoles:
The amount of conc. Of osmotically active particles are usually
expressed in osmoles(osm)
gram molecular weight(i.e one mole)
1 osmole =
no. of freely movable particles, each molecule liberates in
solution

25. Concept of pH & H+ concentration
• pH stands for power of hydrogen
• Refers to negative logarithm of the H+
i. pH= log10 1/[H+]
ii. pH= - log10[H+]
• For decrease in each pH unit (from 7 to 6, [H+] is increased 10 fold vice
versa
• pH & [H+] are inversely related
• Advantage of pH concept : when pK of buffer system is known, it is
immediately possible to determine effective pH range of the buffer
• K= ionisation or dissociation constant
• pK= negative log of K (-log K) & is equal to the pH at which half of the acid
molecules are dissociated & half undissociated

26. • Blood pH always refers to plasma pH(7.4)
• Range of [H+] compatible with life is 20-126 mEq/L i.e pH 7.7 to 6.9
• Optimum pH range at which human body functions properly is 7.45
• Clinically blood pH <7.35 is referred as acidosis
• Blood pH > 7.45 as alkalosis

27. Concept of buffer system
• A buffer is a substance that has ability to bind or release H+ in
solution
• Buffer is solution consist of a weak acid & its conjugate base, keeping
pH of solution constant
• It is a primary means by which large changes in [H+] are minimized
within a fraction of seconds

28. Dynamics of buffering
• Handerson- Hasselbalch Equation
• HA H+ + A-
• A- represent any anion & HA the undissociated acid

29. Handerson Hasselbalch equation

30. • Text book of Medical Physiology
• Guyton & Hall
• Text book of Medical Physiology
• A.K.Jain
• Text Book of Medical Physiology
• Sembulingam
• Net sources

31. Thank you