This document discusses body fluids and their composition and movement within the body. It covers the following key points: - The body maintains fluid balance through intake of water and electrolytes and output through urine, sweat, and feces. Total daily water intake is around 2,500ml while output is also around 2,500ml. - Body fluids are contained within two main compartments - intracellular fluid (ICF) and extracellular fluid (ECF). ICF makes up around 28 liters and ECF makes up around 14 liters. ECF is further divided into interstitial fluid and plasma. - Movement of fluid between compartments is determined by osmotic forces and hydrostatic pressures across semiper

1. Body Fluids
Dr Tuntufyege Mwasanjobe

2. Outline
• Fluid in take and output
• Body fluid compartments
• Measurement of body fluid compartments
• Composition of body fluid compartment
• Movement of fluid in compartment

3. Introduction
• Maintenance of relatively constant and stable composition
of the body fluid is essential for homeostasis
• Failure lead to rise
– Many common and important problems in clinical medicine

4. Fluid Intake and Output
• In steady state
• Exchange of fluid and solute occur with
– The external environment and
– Within the different compartments
• Fluid intake is variable hence must be carefully matched
with output

5. Daily in take of water
• Two major sources of water in the body
– Ingestion (liquids or water in food)
• Add to body fluid total of 2200ml/day
– Metabolism(oxidation of carbohydrates)
• Adding 300mls/day
– Total water intake is 2500mls/day
• Variable between different people and the same person
– Depends on climate, habit and level of physical activity

6. Daily loss of body water
• Insensible water loss -evaporation from the respiratory
and diffusion from the skin
– Account for 800ml/day(respiratory-400ml-400ml)
• Fluid loss through sweating -100mls/day
– Variable depending on the
– Physical activity and environmental temperature
– In hot weather or heavy exercise
• 1 to 2 lts/hour

7. Daily loss of body water
• Water loss in feces
– Normally 100mls/day
• Increase in severe diarrhea
• Water loss by the kidney
– Remaining water loss occur in urine excreted by kidney
• Normally 1500mls
– Vary low as 0.5Lt/day and high as 20lts/day in excessive fluid in
take
• Total 2500mls/day

8. Body fluid compartments
• Total body fluid distributed
between two main compartment
– Intracellular fluid compartment
• Fluid inside the cells
– Extracellular fluid compartment
• Interstitial fluid
• Blood plasma
• Transcellular fluid(synovial, peritoneal,
pericardial, intraocular and CSF)

9. Total body water
• In 70kg adult man
– Total body water is 60% of body weight or about 42 liters
– Depends on age, gender and degree of obesity( amount of fat)
• In women total body water average about 50% of the
body weight due to more percent in fat than men
• In premature and newborn total body water ranges from
70% to 75% of body weight

10. Total body water
• There is increase of the average body weight in many
countries
• Currently average body weight for men older than 20
years in the united state is estimated
• Approximately 86.4 kg in men and 74.1 kg in women
• Need for adjustment when considering body fluid
compartments in most people

11. INTRACELLULAR FLUID COMPARTMENT
• 28 liters of the 42 liters are in side the 100 trillion cell
• Constitute
– 40% of total body weight(70 kg)
– 2/3 of total body water(60% of body water)
• The fluid of each cell
– contains its individual mixture of different constituents
– concentrations of these substances are similar from one cell to
another and similar composition in different
animals(microorganism to humans)

12. INTRACELLULAR FLUID COMPARTMENT
• For this reason, the
intracellular fluid of all the
different cells together is
considered to be one large
fluid compartment

13. EXTRACELLULAR FLUID COMPARTMENT
• All fluid out side the cell collectively
called Extra cellular fluid
• 20% of total body weight ( 14 liters)
• Interstitial fluid
– > ¾ of ECF (11 liters)
• Plasma
– ¼ of ECF (3 liters)
– Noncellular part of blood

14. EXTRACELLULAR FLUID COMPARTMENT
• Exchange substances with the interstitial fluid through
pores of capillary membrane
• Highly permeable to all solutes than protein
• ECF are constantly mixing
– Plasma and interstitial fluids have about the same composition
except for protein(higher in plasma)

15. Source : guyton
and hall ed 13 pg
306
Intake-2200mils
Metabilism-300
Kidiney-1500mils
Lungs-400mils
Skin-400mils
Sweat-100mils
Feces-100mils

16. Blood volume
• Consists of
– ECF (plasma) and ICF(RBCs)
• Separate fluid compartment
– Contained in a chamber of its own, the circulatory system
• 7% of total body weight (5 liters)
• 60% plasma and 40% RBCs
• Vary in different people depends on
– Age ,gender, weight and other factors

17. Blood volume
• Hematocrit (packed RBCs)
– Determined by centrifuging blood in hematocrit tube until cells
are packed to the bottom of the tube
– 3% to 4% of plasma is entrapped among cells
– Hematocrit is 96% of the packed RBCs
– In severe anaemia hematocrit decrease
– In polycythemia hematocrit increase

18. Composition of ECF
• Plasma and interstitial are separated by highly permeable
membrane their ionic composition are similar
• Protein less permeable , plasma has higher concentration
and small amount of protein leaked into interstitial space
• For practical purpose
– The concentration of ions in the interstitial fluid and in the
plasma is considered to be about equal.

19. Composition of ECF
• ECF contain larger amount of
– Sodium and chloride
• Reasonably amount of
– bicarbonate
• Small quantities of
– Potassium,calcium,magnesium,
phosphate and organic ions

20. Composition of ICF
• Intracellular contain
• Larger amount of
– Potassium, phosphate and protein
• Moderate of
– Magnesium and sulfate ions
• Small amount of
– Sodium,chloride almost no calcium

21. Composition of body fluid

23. Measurement of Body Fluid
• The volume of a fluid compartment in the body can be
measured by placing an indicator substance in the
compartment
• Allowing it to disperse evenly throughout the
compartment’s fluid, and then
• Analyzing the extent to which the substance becomes
diluted

25. Measurement count….
• Dilution principle
• Based on conservation of mass principle, which means
that the total mass of a substance after dispersion in the
fluid compartment will be the same as the total mass
injected into the compartment.

26. Measurement count….
• A small amount of dye or other
substance contained in the
syringe is injected into a
chamber and
• The substance is allowed to
disperse throughout the
chamber until it becomes mixed
in equal concentrations in all
areas

27. Measurement count….
• If none of the substance leaks out of the compartment
• The total mass of substance in the compartment (Volume
B × Concentration B) will equal the total mass of the
substance injected (VolumeA × Concentration A).

28. Measurement count….
• For example, if 1 milliliter of a solution containing10 mg/ml
of dye is dispersed into chamber B and the final
concentration in the chamber is 0.01 mg/ml of fluid, the
unknown volume of the chamber can be calculated as
follows:
– Volume of a dye = 1milliliter,
– concentration of dye before dilution =10mg/mil
– Concentration after dilution(dispersed) =0.01 mg/ml

29. Measurement count….

31. Measurement count….
• Total body water
– Radioactive water used to measure
• Tritium 3H2O or Heavy water (deuterium 2H2O) and antipyrine
• Calculated using the dilution principle
• Extra Cellular Fluid
– Estimated using any substance that disperse plasma and
interstitial but do not permeate the cell membrane
– They include radioactive sodium, radioactive chloride,
radioactive iothalamate, thiosulfate ion, and inulin.

32. Measurement count….
• Intra Cellular Volume
– Can not be measured directly
– Is calculated as
• Intracellular volume=total body water-Extra Cellular Volume
• Plasma Volume
– Substance does not penetrate the capillary membrane
– Serum albumin labeled with radioactive iodine(131 I- Albumin)
dye bind avidly to plasma protein(Evans blue dye-T-1824)

33. Measurement count….
• Interstitial fluid volume
– Can not be measured directly
– Calculated as
• Interstitial fluid volume=ECF Volume-Plasma Volume
• Blood Volume
– If plasma volume is measured and hematocrit is known
– Blood volume can be calculated using the equation

34. Measurement count….
• For example, if plasma volume is 3 liters and hematocrit
• is 0.40, total blood volume would be calculated as

35. Properties of indicator substance
• It must
– Be non toxic
– Achieve rapid and even distribution throughout the
compartment
– Not enter any other compartment
– Not be metabolized or synthesized
– Not be excreted
– Be easy to measure
– Not interfere with body fluid distribution

37. Movement of fluid between plasma and ISF
• Extracellular fluid distributed between the plasma and
interstitial spaces
• Determined mainly by the balance of
– Hydrostatic pressure
– Colloid osmotic forces
• across the capillary membranes.

38. Movement of fluid between plasma and ISF
• Determined by the four starling forces
• Capillary pressure (Pc) tends to force
fluid outward through the capillary
membrane
• Interstitial fluid pressure(Pif) tends to
force fluid inward through the capillary
membrane when Pif is positive but
outward when Pif is negative.

39. Movement of fluid between plasma and ISF
• The capillary plasma colloid
osmotic pressure (Πp) tends to
cause osmosis of fluid inward
through the capillary membrane.
• The interstitial fluid colloid
osmotic pressure (Πif), tends to
cause osmosis of fluid outward
through the capillary membrane.

40. Movement of fluid between plasma and ISF
• If the sum of these forces—the net filtration pressure—is
positive, there will be a net fluid filtration across the
capillaries.
• If the sum of the Starling forces is negative, there will be a
net fluid absorption from the interstitial spaces into the
capillaries
• The net filtration pressure (NFP) is calculated as

41. Fluid Exchange Between ICF and ECF
• Distribution of fluid between ICF and ECF is determined
by osmotic effect of smaller solutes
– Sodium ion, chloride ion and other electrolytes
• Membrane is highly permeable to water and relatively
impermeable(selective permeable) to ions
• Water move across the membrane rapidly to maintain
isotonic concentration between the ICF and ECF

42. Osmosis and Osmotic pressure
• Osmosis is the movement (diffusion) of pure solvent
(water) from a solution of low solute concentration to
solution of high solute concentration
• Osmotic pressure is the minimum pressure which needs
to be applied to a solution to prevent the inward flow of its
pure solvent across a semipermeable membrane or
• Is the measure of the tendency of a solution to take in
pure solvent by osmosis

43. Osmosis and Osmotic pressure
• Membrane relatively permeable to
solutes and highly permeable to
water
• Whenever there is high
concentration of solute on one of
the cell membrane water diffuse
across the membrane towards the
side of high concentration until
water concentration between the
two sides becomes equal

44. Osmosis and Osmotic pressure
• If sodium chloride is added to the
extracellular fluid
– water rapidly diffuses from the cells
through the cell membranes into the
extracellular fluid until the water
concentration on both sides of the
membrane becomes equal
– Cause Cells to shrink
ICF
ECF
capillary
Selectivelypermeable
cell membrane
[NaCl]
H2O

45. Osmosis and Osmotic pressure
• if sodium chloride is removed from
the extracellular fluid
– water diffuses from the extracellular
fluid through the cell membranes and
into the cells.
– Cause Cells to swelling
ICF
ECF
Selectivelypermeable
cell membrane
[NaCl]
H2O

46. Osmolarity of the body fluids
• Osmolarity referrers to the number of solute particles per
litter of a solution
• 80% of total osmolarity of ISF and plasma due to Na+ &
Cl-
• Half of osmolarity of ICF is due to K+
• Total osmolarity in each of the three compartment is
300mOmol/L

47. Osmotic equilibrium between ECF and ICF
• Large osmotic pressures can develop across the cell
membrane with relatively
• small changes in the conc of solutes in the ECF
• 1mOsm/L conc gradient of an impermeant solute
• About 19.3 mmHg of osmotic pressure is exerted across
the cell membrane

48. Osmotic equilibrium between ECF and ICF
• If the cell membrane is exposed to pure water and
– the osmolarity of ICF= 282 mOsm/L,
• The osmotic pressure that can develop across the cell
membrane =282*19.3=5442
• If ICF and ECF are not in osmotic equilibrium
• Larger force can develop that can move water into the cell

49. Isotonic,Hypotonic and Hypertonic solution

50. Isotonic,Hypotonic and Hypertonic solution
• If a cell is placed in isotonic solution of impermeant
solutes having an osmolarity of 282 mOsm/L,
– the cells will not shrink or swell
– because the water conc in the ICF and ECF is equal
• the solutes cannot enter or leave the cell. .
• Examples
– 0.9 percent solution of sodium chloride or a
– 5 percent glucose solution.

51. Isotonic,Hypotonic and Hypertonic solution
• If a cell is placed into a hypotonic solution that has a lower
concentration of impermeant solutes (<282 mOsm/L)
– water will diffuse into the cell, causing it to swell
• water will diffuse into the cell, diluting the ICF while also
concentrating the ECF until both solutions have about the
same osmolarity.
• Solutions of sodium chloride with a concentration of less
than 0.9 percent are hypotonic and cause cells to swell.

52. Isotonic,Hypotonic and Hypertonic solution
• If a cell is placed in a hypertonic solution having a higher
concentration of impermeant solutes,
• water will flow out of the cell into the ECF, concentrating
the ICF and diluting the ECF.
• The cell will shrink until the two concentrations become
equal.
• Sodium chloride solutions of greater than 0.9 percent are
hypertonic.

53. EFFECT OF ADDING SALINE SOLUTION TO ECF

54. EFFECT OF ADDING SALINE SOLUTION TO ECF
• If isotonic saline is added to the ECF compartment
– No change in osmolarity
– no osmosis occurs through the cell membranes.
– Increase in extracellular fluid volume
• The sodium and chloride largely remain in the
extracellular fluid because the cell membrane behaves as
though it were virtually impermeable to the sodium
chloride.

55. EFFECT OF ADDING SALINE SOLUTION TO ECF
• If a hypertonic solution is added to the ECF,
– the extracellular osmolarity increases and
– causes osmosis of water out of the cells into the extracellular
compartment to achieve osmotic equilibrium
• Almost all the added NaCl remains in the ECF
• The net effect is an increase in extracellular volume a
decrease in intracellular volume, and a rise in osmolarity
in both compartments.

56. EFFECT OF ADDING SALINE SOLUTION TO ECF
• If a hypotonic solution is added to the extracellular fluid,
– the osmolarity decreases
– water diffuses into the cells until the intracellular and
extracellular compartments have the same osmolarity
• Both the intracellular and the extracellular volumes are
increased by the addition of hypotonic fluid, although the
intracellular volume increases to a greater extent

57. references
• Guyton and Hall Textbook of Medical Physiology

58. Thank you