Body Fluid: Distribution and Measurement

Soumen  Manna

SECTION 1

1General Physiology

Body Fluid: Distribution and Measurement
Cell Membrane, Transport and Membrane potential

Body Fluid: Distribution and Measurement1

BODY COMPOSITION (AS % OF BODY WEIGHT)

Human body is composed of the following:

Atomic/ Elementary level		Molecular or, chemical level		Histology/Tissue level
Oxygen	60%	Water	60%	Skeletal muscle	36%
Carbon	20%	Protein	18%	Non-skeletal	29%
Hydrogen	15%	Fat	15%	Adipose tissue	25%
Calcium	1%	Mineral	6%	Bone	10%
Others	4%	Glycogen	1%

Body Water as % Body Weight

TBW = 60%
1. ICF = 40% (2/3rd of TBW)
2. ECF = 20% (1/3rd of TBW)
  1. Plasma = 5% (1/4th of ECF)
  2. Interstitial fluid = 15% (3/4th of ECF). It includes lymph also, which is 2–3% of total body weight.
  3. Transcellular fluid = ~1.5%
Total blood volume = 8% of body weight (Since, plasma volume = 5% of body weight and blood cell volume = 3% of body weight)

Transcellular Fluid

This compartment includes fluid in the synovial, peritoneal, pericardial, and intraocular spaces, as well as the cerebrospinal fluid; it is usually considered to be a specialized type of ECF, although in some cases, its composition may differ markedly from that of the plasma or ISF. All the transcellular fluids together constitute about 1 to 2 liters (1% to 3% of body weight).

Pericardial fluid: 50 ml
Pleural fluid: 10–20 ml4
Peritoneal fluid: Male–no fluid, Female–20 ml (early luteal phase) and 5 ml (late luteal phase).
Synovial fluid:
- About 1ml of fluid is present in each large joint like knee, hip, ankle, shoulder, elbow and wrist. (Range 0.5 ml to 1.5 ml). In Osteoarthritis it may be upto 100 ml.

The normal internal cell functions depend upon the consistency of the fluid that forms the actual immediate environment of the cells. For this reason the extra-cellular fluid environment, more particularly the interstitial fluid is known as “milieu interieur”, a term coined by Claude Bernerd.
Maintenance of the internal milieu was first called the “wisdom of the body” by Starling.
The term homeostasis was later coined by Walter Cannon to describe the physiologic processes that, in aggregate, maintain the constancy of the internal chemistries, as well as BP, body temperature, and energy balance.

Measurement of Body Fluid

The volume of water in different compartment can be measured by Volume of distribution principle (indicator dilution principle).

Where,

ν = Volume of fluid
Q = Quantity of indicator given
C = Concentration of the indicator
e = The amount of indicator which has either been lost or metabolized

Substances Used for Measurement of Various Compartments

Compartment	Indicator used
Plasma volume	Evans’ blue (T1824), ¹²⁵I-albumin (most commonly used)
RBC volume	Tagging RBC with ⁵¹Cr, ⁵⁹Fe, 32P; also antigenic tagging
Total blood volume	Plasma volume / (1-Hematocrit)
ECF volume	Inulin, sucrose, Mannitol, Sodium thiosulphate, sodium thiocyanate, ²²Na, ¹²⁵I-iothalamate
Interstitial fluid	Cannot be measured directly; can be calculated as (ECF volume–Plasma volume)
ICF	Cannot be measured directly; can be calculated as (Total body water–ECF)
Total body water	D₂O is most frequent used; also, tritium oxide, antipyrine

Some Important Aspects of Body Fluid

Women have less body water than men, because women have proportionately more fat (a tissue with low water content).
After 40 years of age, the mean value for TBW in percentage of total body weight decrease in both men and women but the sex difference remains.5

Age	~ Total Body Water (As % of body weight)
Premature infant	90%
Full term Newborn	70-80%
One year	64%
Puberty to 39 years	Men: 64% Women: 52%
40 to 60 years	Men: 55% Women: 47%
>60 years	Men: 52% Women: 46%
Ref: Fluid and Electrolyte Balance By Norma M. Metheny

Infant contains proportionately more body fluid than adult and relatively more fluid in extracellular compartment (prone to dehydration).
By the age of two years, body fluid % approaches the adult %.
At puberty, for the first time there is a sex difference of fluid content.
Water content of lean body mass = 71-72 mL/ 100 gm of tissue (Lean body mass = body mass devoid of fat)
Fat tissue contains 20% of water, while muscle contains 65% of water.

Normal Fluid Balance in Body

Daily intake of water: Total 2300 ml (Fluids ingested 2100 ml and from metabolism 200 ml)
Daily loss of water:
- Insensible Water Loss 700 ml (from skin 350 ml and from lungs 350 ml)
- Sweat 100 ml
- Feces 100 ml
- Urine 1400 ml

Shifts of Water between Compartments

It is important to understand how volume and osmolality of ECF and ICF in abnormal states changes. The relationship is easily explained by Darrow-Yannet Diagram, which is explained below:

Remember:
- Water moves rapidly across cell membranes; therefore, the osmolarities of ICF and ECF remain almost exactly equal to each other except for a few minutes after a change in one of the compartments.
- Cell membranes are almost completely impermeable to many solutes; therefore, the number of osmoles in the ECF or ICF generally remains constant unless solutes are added to or lost from the ECF compartment.6
Y-axis: solute concentration or, osmolality
X-axis: Volume of ICF (2/3) and ECF (1/3)
- In normal control state, osmolality of ICF and ECF is equal.
- Whenever any solution is added or, lost from body, its changes the ECF volume or, osmolality or, both according to the type of solution (isotonic, hypotonic or, hypertonic).
- ICF volume varies with ECF osmolality and ICF osmolality changes inversely to volume change.

Now Carefully Check the Following Diagrams

(Broken line indicates shifts from normal).

Gain of Isotonic Fluid (B)

Infusion of isotonic solution will lead to increase ECF volume but no change in osmolality. Because there is no change in osmolality, ICF volume remains same.

Loss of Isotonic Fluid (C)

Will only decrease the ECF volume.

Gain of Hypotonic Fluid (D)

It increases the ECF volume, but because of its hypotonicity, the final osmolality of ECF decreases. Water shifts from ECF to ICF (osmosis), which leads to increase ICF volume. Because its only shift of water from ECF to ICF, osmolality of ICF reduces until new equilibrium reached.

Loss of Hypotonic Fluid (E)

Hypotonic loss leads to decrease volume but increase osmolality of ECF. Water shifts from ICF to ECF (osmosis), which decrease ICF volume.

Gain of Hypertonic Fluid (F)

Increase in effective volume and osmolality of ECF. Water shifts from ICF to ECF, which leads to decrease ICF volume and increase osmolality until new equilibrium reached.

Loss of Hypertonic Fluid (G)

Decrease ECF volume and tonicity because of hypertonic fluid loss. Decrease tonicity of ECF, shifts the fluid from ICF to ECF (osmosis). So, ICF volume increases and tonicity decreases.

SUMMARY OF DARROW-YANNET DIAGRAM

Type (diagram no)	Example	ECF volume	ICF volume	ECF Osmolarity
Gain of isotonic fluid (B)	Isotonic NaCl infusion	Increased	No change	No change
Loss of isotonic fluid (C)	Hemorrhage Diarrhea Vomiting	Decreased	No change	No change
Gain of hypotonic fluid (D)	SIADH Drinking of tap water	Increased	Increased	Decreased
Loss of hypotonic fluid (E)	Sweating, Diabetes insipidus	Decreased	Decreased	Increased
Gain of Hypertonic fluid (F)	Excessive NaCl intake, mannitol	Increased	Decreased	Increased
Loss of Hypertonic fluid (G)	Adrenocortical insufficiency	Decreased	Increased	Decreased

Hypotonic fluid distributed both in ECF and ICF

Example: If there is loss of 1 L of water (hypotonic), isotonic NaCl, or half-isotonic NaCl fluid from body, calculate amount of ECF loss in all three conditions.

Water loss: If 1 L of water is lost, the ICF volume will decrease by 667 mL, whereas the ECF volume will fall by only 333 mL.
Isotonic loss: ECF volume will decrease by 1 L, no change in ICF volume.
Half-isotonic loss: One liter of half-isotonic NaCl is equivalent to 500 mL of water plus 500 mL of isotonic saline. So, 500 ml water will be lost from ECF and ICF. And another 500 ml will be lost from ECF only. Therefore, the loss of 1 L of half-isotonic saline decreases the ECF and ICF volumes by 667 mL and 333 mL, respectively.

COMPOSITION OF DIFFERENT FLUID COMPARTMENT

ECF

Ionic composition of plasma and interstitial fluid (ISF) is similar.

The most important difference between these two compartments is the higher concentration of protein in the plasma.
Because of the Donnan effect, negatively charge plasma protein holds a slightly greater (~2%) cations in the plasma than in the interstitial fluid.

ICF

Only small quantities of Na⁺ and Cl^- ions and almost no Ca⁺⁺ ions. Instead, it contains large amounts of K⁺ and phosphate ions plus moderate quantities of Mg⁺⁺ and sulfate ions. Also, cells contain large amounts of protein, almost four times as much as in the plasma.

TYPICAL IONIC CONCENTRATION OF MAMMALIAN CELL

Ion	Cell (ICF) in mOsm/L	ISF in mOsm/L	Blood (ECF) in mOsm/L
K⁺	140 (max cation)	4	4.2
Na⁺	14	139	145 (max cation)
Cl^–	4	108	108 (max anion)
HCO₃^–	10	28	24
HPO₄, H₂PO₄	11 (max anion)	2	2
Protein	4	0.2	1.2
Ca²⁺	<0.0002	1.2	1.8
Mg²⁺	20	0.7	1.5
Corrected osmolar activity (mOsm/L)	281	281	282
Total osmotic pressure at 37°C (mm Hg)	5423	5423	5443

Concentration gradient between ECF and ICF is maximum for Ca⁺⁺ (~12000:1)9

In an average 70-kg adult, the whole-body:

Sodium content: 3500 to 5000 mEq (mMol), which is ~58mEq/kg body weight. Of this amount, 90% is in the ECF compartment and 10% is in the ICF compartment (primarily in the Bone). Daily turnover is 4%.
Potassium content: 3000 to 3750 mEq (mMol), which is ~53 mEq/kg body weight. Of this amount, 98% is in the ICF compartment (primarily in the muscle) and 2% is in the ECF compartment. Because plasma constitutes 1/4th of ECF, K⁺ content of plasma will be 0.5% of total body K⁺. Daily turnover is 2.3%.
Calcium content: 60,000 mEq, with a daily turnover of 0.01%.
Magnesium content: 2000 mEq with a turnover of 0.5%.
Phosphate content: 18,000 mMol with a turnover of 0.17%.

It is important to note that:

Essentially all of the body K⁺ is in the exchangeable pool.
Only 65–70% of the body Na⁺ is exchangeable.
Almost all of the body Ca²⁺ and Mg²⁺ are non-exchangeable.
Only the exchangeable solutes are osmotically active.

UNITS OF MEASUREMENTS

Moles

A mole is the molecular weight of the substance in grams. Each mole (mol) consists of 6 × 10²³ molecules. The millimole (mmol) is 1/1000 of a mole, and the micromole (μmol) is 1/1,000,000 of a mole.

Example: 1 mol of NaCl = 23 g + 35.5 g = 58.5 g, and 1 mmol = 58.5 mg. (Atomic weight of Na = 23 and CL = 35.5)

EQUIVALENTS

One equivalent (Eq) is 1 mol of an ionized substance divided by its valence.

Examples: One mole of NaCl dissociates into1Eq of Na+ and1Eq of Cl^–. One equivalent of Na⁺ = 23g, but 1 Eeq of Ca²⁺ = 40 g/2 = 20 g.

OSMOLE

It expresses concentration of osmotically active particles.

1 Osmole = Mol /Number of freely moving particular each molecule liberates in solution

Examples:

1 mol of NaCl = 2 osmoles because each NaCI molecule given one Na⁺ and one Cl^- particle is solution.
1 mol of Na₂SO₄ = 3 osmoles because each Na₂SO₄ molecule gives 2 Na⁺ and 1 SO₄ in solution
1 mol of, CaCl2 = 3 osmoles, because each molecule of CaCl2 give 3 particles (1 calcium and 2 Cl^-) in solution.10

CONVERTING WEIGHT TO OSMOLALITY

CONVERTING WEIGHT TO MILLIEQUIVALENTS

Example A: Convert the expression 10 mg% of Ca⁺⁺ to mEq/L and mOsmol/L

10 mg% of Ca⁺⁺ means, 10 mg/100 ml= 100 mg/L

Example B: How many mEq of KCl are in 1.5 g of KCl

Molecular weight of KCL = 39 + 35.5 = 74.5

Example C: 100 mg each of NaCl, CaCl₂ and FeCl₃ in 1L of water. Determine the concentration in percent, molarity, milliequivalent (mEq) and milliosmolarity (mOsmol).

Percent (g/volume)

NaCl: 100 mg of NaCl in 1L solution = 0.1g/1000 ml= 0.01 g/100 ml = 0.01%
CaCl₂: 100 mg of CaCl₂ in 1L solution = 0.1g/1000 ml= 0.01g/100 ml = 0.01%
FeCl₃: 100 mg of FeCl₃ in 1L solution =0.1g/1000 ml= 0.01g/100 ml = 0.01%
Molarity NaCl: Molecular weight = 58.5 g (so, 1Mol = 58.5 g) 0.01g/58.5 g = 0.0017 M = 1.7 mMol
CaCl₂: Molecular weight = 111 g (so, 1Mol = 111 g) 0.01g/111g = 0.0009 M = 0.9 mMol
FeCl₃: Molecular weight = 162.2 g (so, 1Mol = 162.2 g) 0.01g/162.2 g = 0.00062 M = 0.62 mMol

Milliequivalent

NaCl: Molecular weight = 58.5g valence 1
CaCl₂: Molecular weight = 111g and valence 2
FeCl₃: Molecular weight = 162.2g and valence 3

Milliosmole

We have already discussed, that 1 mol of NaCl = 2 osmoles, 1 mol of, CaCl₂ = 3 osmoles. Similarly 1 mol FeCl₃ = 4 osmoles.

So,

1.7 mM of NaCl = (2 × 1.7) mOsmol = 3.4 mOsmol/L

0.9 mM of CaCl₂ =(3 × 0.9) mOsmol = 2.7 mOsmol/L

0.62 mM of FeCl₃ = (4 × 0.62) = 24.8 mOsmol/L

Or, directly using the formula

result.

TONICITY

Definition: This is the osmolality of a solution with respect to plasma osmolality.

Example: 0.9% NaCI is isotonic; 5% glucose is isotonic initially; later has become hypotonic.

Calculated Osmolarity (CO)/Osmolality

When unit of Na and K are in mEq/L or, mmol/L, and unit of Glucose and BUN are in mg/dl

When all units are in mmol/L:

Measured osmolality (MO)

The most accurate way of finding out the osmolality is by freezing point depression.

OSMOLAL GAP

If there is a difference between the CO and MO, it is called osmolal gap. Osmolol gap indicates the presence of a foreign substance like usually a toxic alcohol such as ethanol, methanol or isopropyl alcohol.

So, sometime a different equation is used when the patient has ingested ethanol, or, mannitol therapy:

The normal osmolality of the ECF and ICF fluids is ~290-290 mOsm kg. In the plasma of the total osmolality Na+, Cl^– and HCO₃– contribute 270 mOsm. The remaining 20 mOsm are contributed by glucose and urea.

Because of the large molecular weight and hence lesser number of particles, plasma proteins (70g/L) contribute 2 mOsm to the total plasma osmolality.
There are altogether, around 36 formulas for osmolality calculation!!!!
The best equation is: Zander's optimized equation, which is not commonly used.
The best method for measurement is: freezing point depression.

TONICITY OF DIFFERENT SOLUTION

	Tonicity	mOsmol/Kg	Glucose (g/L)	Comments
Dextrose solution
5%	Isotonic but physiologically hypotonic	278	50	Provide 170 Cal/L
10%	Hypertonic	556	100	Provide 340 Cal/L
Saline solution
0.45%	Hypotonic	154	0	No Calories
0.9%	Isotonic	308	0	Only solution that may be administered with blood product
3%	Hypertonic	1026	0	No Calories
Dextrose in saline
5% in 0.225%	Isotonic	355	50	Provide 170 Cal/L
5% in 0.45%	Hypertonic	432	50	Provide 170 Cal/L
5% in 0.9%	Hypertonic	586	50	Provide 170 Cal/L
13
Multiple electrolytes solution
Ringer's solution	Isotonic	309	0	Similar in composition to plasma except it has excess Cl^- and No Mg⁺⁺, no HCO₃^–
Lactate Ringer's (Hartmann's Solution)	Isotonic	274	0	Similar in composition to plasma except it has No Mg⁺⁺

BODY FLUIDS

RECENT MCQs

1. Volume of ICF in body:

0.2 × body wt.
0.4 × body wt
0.6 × body wt.
0.8 × body wt.

2. ECF is how much part of total body weight:

One third
Half
Two third
None

3. ICF is:

14 L
20 % of body weight
28 L
33% of body weight

4. Major cation in ECF:

Na⁺
K⁺
Ca⁺⁺
Mg⁺⁺

5. Most osmotically active intracellular cation:

K⁺
Na⁺
Mg⁺²
Protein

6. True regarding Na⁺ ion

Responsible for Donnan effect
Responsible for Resting membrane potential
Responsible for Depolarization
Does not help other ions in trans port

AIIMS/PGI/JIPMER

7. The following are true about body water [PGI Dec 07]

Water constitutes 60% of the body weight
Plasma volume constitutes 10% of the total body water
ECF volume can be determined by dilution methods
10% is intracellular water

8. ECF forms what percentage of body weight [AI 97]

10 %
25%
33 %
60%

9. True statements are: [PGI Dec 04]

Total body water constitutes about 60% of body weight
Most intracellular water is the musculoskeletal system
Extracellular water constitutes about 40% of body weight
Total plasma constitutes about 10% body weight
Extracellular fluid can be measured by dilution method

10. Which of the following methods is not used for measurement of body fluid volumes? [AIIMS May 05]

Antipyrine for total body water
Inulin for extracellular fluid
Evans blue for plasma volume
I¹²⁵ albumin for blood volume14

11. Most accurate measurement of extracellular fluid volume (ECF) can be done by using: [AIIMS May 03]

Sucrose
Mannitol
Inulin
Aminopyrine

12. Predominant extracellular ions are:

Na⁺
K⁺
Cl^-
HCO₃^-
PO₄

13. True statements about ions composition in body: [PGI June 06]

Intracellular & Extracellular ions compositions are same
Phosphorus and Mg⁺⁺ are major ions intracellularly
Na⁺, Cl^– principal ions in ECF
Kidney tightly regulates Na⁺, K⁺, Cl^- composition

14. About sodium, true: [PGI Dec 07]

Normal serum level is 135-145 mEq/L
Daily intake is 150 mmol of NaCl
Major portion is extracellular
Major reserve is skeletal muscle

15. Total body water differences between male and female is not seen at the age of [JIPMER]

Above 60 years
40- 60 years
10-18 years
18- 25 years

16. Osmotic pressure of 1 mole of ideal solute relative to pure water is: [PGI May 09]

6.5 atm
22.4 atm
4 atm
l atm
2 atm

17. Ineffective osmols is [JIPMER 02]

Na⁺
K⁺
Urea
All

FUTURE TRENDS

18. One person has ingested 1500 ml of water. Calculate the amount that will be present in ISF after equilibrium?

1000 ml
500 ml
375 ml
125 ml

Answer questions number 19 and 20 from the following diagram (dashed lines represent original conditions and solid lines the final steady-state situation).

19. Which of the diagram best illustrates the fluid shifts resulting from infusion of 1L of distilled water into the bloodstream:

20. Which best illustrates the status of a person who received 1 L of a hypertonic saline solution intravenously.

21. A 60 kg patient has a hematocrit reading of 40 and a plasma volume of 3 liters. What is his total blood volume?

4.0 liters
5.0 liters
6.0 liters
7.0 liters

22. What is the calculated osmolarity of a solution containing 12 mmol NaCl, 4 mmol KCl and 2 millimolar CaCl2 (mOsmol/L)?

16
26
38
3215

23. Assuming complete dissociation of all solutes, which of the following solutions would be hyperosmotic to 1 mM NaCl?

1 mM glucose
1.5 mM glucose
1 mM CaCl2
1 mM sucrose

24. Which of the following best describes the changes in cell volume that will occur when red blood cells (previously equilibrated in a 280-mOmol solution of NaCl are placed in a solution of 140 mmol NaCl containing 20 mmol urea, a relatively large but permeant molecule?

Cells shrink initially, then swell over time and lyse
Cells shrink transiently and return to their original volume over time
Cells swell and lyse
No change in cell volume will occur

The diagram below illustrates possible changes in RBC volume resulting from a change in ECF composition for a cell equilibrated in 150 mM/L NaCl solution at time 0. Answer questions number 25 and 26 below:

25. Which curve best illustrates the volume caused by immersion of the cell into an aqueous solution of 300 mOsm CaCl2

26. Which curve best illustrates the volume change caused by immersion of the cell into a mixture of aqueous solution of 200 mOsm/L NaCl and 200 mOsm/L of glycerol?

ANSWERS

Ans. b.0.4 x body wt

(Ref: Ganong's Physiology 24th ed. pp 2)

ICF is 40% of total body weight.

Ans. d.None

(Ref: Ganong's Physiology 24th ed. pp 2)

ECF is 20% of total body weight, so, its 1/5th of body weigth and 1/3^rd of total body water (33%)

Ans. c.28 L

(Ref: Ganong's Physiology 24th ed. Pp 2)

ICF is 40% of total body weight. Adult person with 70 Kg body weight, total body water is 42 L and ICF (2/3^rd) volume is 28L

Ans. a. Na⁺

(Ref: Ganong's Physiology 24th ed. pp 3)

In ECF Major cation is Na⁺ and anion is Cl^-. In ICF major cation is K⁺ and anion is phosphate.

Ans. a. K⁺

(Ref: Ganong's Physiology 24th ed. pp 2)

Osmolality depends on number of molecules. As K⁺ concentration is maximum in cell, most osmotically active particle is K⁺

Ans. c. Responsible for Depolarization

(Ref: Ganong's Physiology 24th ed. pp 6)

Donnan effect is distribution of all permeable ions due to presents of non-permeable ions. K⁺ is responsible for RMP.

Ans. a.Water constitutes 60% of the body weight

(Ref: Ganong's Physiology 24th ed. pp 2)16

c. ECF volume can be determined by dilution methods

Plasma volume is 5% of total body weight. In a 70 kg person, plasma volume is 3.5L and total body water is 42L (60% of body weight). So, plasma is 8.3% of total body water [(3.5/42)×100]

Ans. b. 25%

(Ref: Ganong's Physiology 24th ed. pp 2)

ECF is 20% of total body weight. So, close answer is 25% with the provided options.

Ans. a.Total body water constitutes about 60% of body weight,
1. Most intracellular water is the musculoskeletal system
1. Extracellular fluid can be measured by dilution method

(Ref: Ganong's Physiology 24th ed. pp 2)

ECF constitute 20% of total body weight. Total plasma is 5% of body weight.

Ans. d.I ¹²⁵albumin for blood volume

(Ref: Guyton-Physiology-13th edn.pp 49)

I¹²⁵ albumin is used for plasma volume not blood volume.

Ans. c.Inulin (Ref: Guyton-Physiology-13th edn.pp 49)

Inulin is best for ECF measurement.

Ans. a. Na⁺ c. Cl^- d. HCO₃^-

(Ref: Ganong's Physiology 24th ed. Pp 3)

Predominant ECF: Na^{+ ,} Cl^-, HCO₃^- and Ca⁺⁺

Predominant ICF: K^+, Mg⁺⁺, phosphate and protein.

Ans. b.Phosphorus and Mg⁺⁺ are major ions intracellularly,
1. Na⁺, Cl^- principal ions in ECF
2. Kidney tightly regulates Na⁺, K⁺, Cl^- composition

(Ref: Ganong's Physiology 24th ed. pp 3)

Ans. a.Normal serum level is 135-145 mEq/L
1. Daily intake is 150 mmol of NaCl
2. Major portion is extracellular

(Ref: Ganong's Physiology 24th ed. pp 3)

Major reserve of Na is bones not muscle.

Ans. c.10-18 years.

(Ref: Fluid and Electrolyte Balance By Norma M. Metheny)

Difference is not seen upto the age of puberty

Ans. b.22.4 atm

(Ref: Guyton's Physiology 12th edn.pp. 299 & 13th edn.pp 51)

“At 37°C, a concentration of 1 osmole per liter will cause 19,300 mm Hg osmotic pressure in the solution. Likewise, 1 mOsmol per liter concentration is equivalent to 19.3 mm Hg osmotic pressure.”

Ans. c.Urea

(Ref: Guyton's Physiology 12th edn. pp. 299 & 13th edn.pp 52)

“Highly permeating substances, such as urea, can cause transient shifts in fluid volume between the ICF and ECF, but given enough time, the concentrations of these substances eventually become equal in the two compartments and have little effect on intracellular osmolality and volume under steady-state conditions.” That's why urea is an ineffective osmoles.

Ans. c.

Water is a hypotonic fluid so, it will be distributed equally in both ECF and ICF according to their volume.

So,

2/3^rd of 1500 ml will be distributed in ICF = 1000 ml
1/3^rd of 1500 ml will be distributed in ECF = 500 ml
ISF is 3/4th of ECF = 3/4th of 500 ml = 375 ml.

Ans. b.

Infusion of distilled water would decrease body osmolarity and increase the volume of the ECF. The decreased ECF osmolarity would cause water to diffuse into cells and raise ICF volume.17

Ans.None

Infusing hypertonic saline will increase body osmolarity. Since fluid is given, the volume of the ECF compartment will increase. The increased osmolarity of the ECF will cause water to diffuse out of cells, decreasing ICF volume. None of the diagram is matching.

Ans. b.

Hematocrit (Hct) = 40% = 0.4

Blood volume = Plasma volume/(1-Hct) = 3/ (1-0.4) = 5L

Ans. c.

1 mmol solution has 1mOsmol when the solute does not dissociate. NaCl and KCl both dissociate into two molecules and CaCl2 dissociae into 3 molecules. So, 12mmol of NaCl has an osmolality of 24 mOsmol, 4 mmol of KCl = 8 mOsmol and 2 mmol of CaCl2 = 6 mOsmol. Total 38 mOsmol.

Ans. c.

The 1 mM CaCl₂ solution (osmolarity = 3 mOsm/L) is hyperosmotic to 1 mM NaCl (osmolarity = 2 mOsm/L). The 1 mM glucose, 1.5 mM glucose, and 1 mM sucrose solutions are hyposmotic to 1 mM NaCl.

Ans. b.

Cell is placed in a solution of 140 mmol NaCl with 20-mmol urea. A solution of 140 mmol NaCl has an osmolarity of 280 mOsmol, which is iso-osmotic relative to “normal” intracellular osmolarity. If RBC were placed in 140 mmol NaCl alone, there would be no change in cell volume. But the additional presence of 20-mmol urea, however, increases the solution's osmolarity and makes it hypertonic relative to the ICF solution. Water will initially move out of the cell, but because the plasma membrane is permeable to urea, urea will diffuse into the cell and equilibrate across the plasma membrane. As a result, water will re-enter the cell, and the cell will return to its original volume. So, B better answer>>D.

Ans. c.

The RBC was equilibrated in 150 mM NaCl (means 300 mOsmol NaCl) that is an isotonic saline solution. A 300 mOsm CaCl₂ solution is also an isotonic solution of a nonpenetrating solute, thus, there will be no change in RBC volume.

Ans. b.

200 mOsm NaCl is nonpenetrating but the 200 mOsm glycerol penetrates slowly. Initially the effective osmolarity of the solution is 400 mOsm (200 Nacl+ 200 glycerol), thus the cell shrinks. With time the glycerol penetrates and the final effective osmolarity of the solution is only 200 mOsm due to the NaCl. Thus, as the glycerol penetrates, water moves into the red blood cell and final volume will be greater than at time zero. Curve B, which shows an initial shrinkage then overall swelling, is the best answer.

Chapter Notes

Body Fluid: Distribution and Measurement1