Practical Laboratories Physiology I [621136]

Practical Laboratories Physiology I
1
EXPLORATION OF FLUID AND ELECTROLYTE BALANCE.
BODY FLUID COMPARTMENTS

Fluid and electrolyte balance is defined by the fol lowing aspects:
• Maintenance of constant volume of body fluid compar tments (water balance);
• Maintenance of constant ions concentration and equa l the sum of anions and cations
amount of plasma (electrolyte balance);
• Maintenance of constant body fluid osmolarity (osmo tic balance).

1. WATER BALANCE

Water balance refers to maintaining within normal l imits the amount of water in the body and
constant body fluid compartment volumes.

1.1. TOTAL WATER

It represents the water content of the body, with w ide limits of variation based on: body
weight (60%), gender, nutritional status of the bod y and age.
Water is distributed in two sectors within the body : intracellular and extracellular.

INTRACELLULAR FLUID COMPARTMENT (ICF) represents 40% of body weight and
is composed of:
• structural water – constitutive water, immovable, fixed on cytoplas m components;
• free water – with the role of dispersion medium in the cytopl asm, movable, involved in
metabolic processes and transcellular exchanges.

THE EXTRACELLULAR FLUID COMPARTMENT (ECF) represents 20% of body
weight and is composed of:
• interstitial fluid compartment which includes interstitial plasma ultrafiltrate, limited by
the cell membrane from intracellular fluid compartm ent and by capillary membrane from
the intravascular compartment. Represents ¾ of extr acellular water. It is quickly
mobilized and participates in exchanges between blo od and cells. Enables exchanges
between them and the external environment through t he external surface (skin), internal
surfaces of exogenous intake (digestive, pulmonary) and epuration surfaces (liver, kidney,
and lung).
• intravascular fluid compartment is represented by the blood plasma and is separate d by
the capillary membrane from interstitial fluid. It is the linking system between the internal
and external environment of the body, which allows nutrients intake and catabolits
elimination. Represents ¼ of extracellular water.

EXAMPLE for an adult male with body weight 70 kg ( Fig.1.):

Total water (60% of body weight)………………. …………………. ………………………. ………….42 liters
Intracellular water (40% of the total water) …………………………………………… ………..28 liters
Extracellular water (20% of the total water) …………………………………………… ……….14 liters
/uni25CF Interstitial fluid compartment (¾ of extracellul ar water)………………….10.5 liters
/uni25CF Intravascular fluid compartment (¼ of extracellu lar water)………………..3.5 liters

Practical Laboratories Physiology I
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Fig. 1. Fluid water distribution sectors.
The values listed are calculated for a 70 kg person .

MEASUREMENT OF FLUID COMPARTMENTS VOLUMES. It can be performed
using the dilution method based on the following principle: in an unknown compartment
volume (V2) introduce a colored or and radio labele d substance, with known V1 volume and
concentration C1 which have the properties to be di stributed homogeneously in the studied
compartment. C2 concentration of the substance afte r dilution is determined with specific
method, and thus volume of fluid compartment can be determined using following formula:
V2 = V 1 x C 1 / C 2
where: V1 = volume of injected substance
C1 = concentration of injected su bstance
C2 = concentration of the substan ce after dilution
V2 = volume of fluid to be determ ined

Substances used to determine the fluid spaces must fulfill the following conditions:
• non-toxic;
• to disperse uniformly in studied compartment;
• to not fix on the capillary endothelium;
• to remain in the studied compartment a sufficient t ime for determination;
• not to metabolize too quickly;
• not to modify its properties;

Practical Laboratories Physiology I
3 The following volumes of fluid compartments can be determined:
• total body water volume → using substances which diffuse through the capilla ry
membrane and cellular membranes after injection int o the blood (tritiated water,
antypirine)
• extracellular fluid volume → using substances which diffuse through the capilla ry
membrane after injection into the blood, but can no t cross the cell membranes (manitol,
inulin)
• intravascular fluid volume (plasma volume) → using substances which after injection into
the blood, do not leave the bloodstream and do not cross the membrane of blood cells
(Congo red, Evans blue)

Volumes of other fluid compartments are obtained in directly by calculation:
• intracellular fluid compartment = total water volume – extracellular fluid volume
• interstitial fluid compartment = extracellular fluid volume – plasma volume

PHYSIOLOGICAL V ARIATION: Body's water content varies depending on:
• age:
– new-born ……………………………….80% o f body weight
– children …………………………….70-75% o f body weight
– adults …………………………………… 6 0% of body weight
– elderly …………………………… … < 60% of body weight
• gender – women have a water content of about 5% less than men
• nutritional status – obesity, due to hydrophobic adipose tissue, caus es a reduction in the
proportion of body water.

1.2. VOLEMIA

DEFINITION. Volemia represents the total blood volume (TBV), i s the sum of plasma
volume (PV) and cells volume (red cells volume) (CV).
TBV = PV + CV

NORMAL VALUES . Normal volemia (normovolemia ) is 3 ± 0.5 litres/m 2 body surface or
78 ml/kg, which represents 7-8% of the body weight. Thus, a 70 kg adult has approximately 5
liters of volume, 3 liters of blood plasma and 2 li ters of blood cells.

PHYSIOLOGIC VARIATIONS . Under certain conditions, maintaining normal leve ls of
total blood volume is achieved by changing the rati o of plasma volume and cell volume. For
example, in anemia decreasing CV will induce an inc rease of PV, while in chronic
cardiopulmonary diseases, increasing CV will decrea se PV. Volemia is amended by:
• gender – volemia is higher in men because of erythropoiesi s adaptation to increased
oxygen consumption caused by a better developed mus cle mass
• age
– new-born = 80-100 ml/kg body weight due to peri-nat al hypoxic conditions which
stimulate erythropoiesis
– adults = 78 ml/kg body weight
• physiological status – increase in pregnancy in the last half of pregna ncy due to water and
saline retention caused by hypersecretion of estrog en and progesterone
• activity status
– in untrained persons volemia decreases by 10% throu gh increased volume of fluid
extravasations into the interstitial space of muscl e
– in trained persons volemia increases with 100 ml/k g by blood mobilization from
storages

Practical Laboratories Physiology I
4 • external conditions
– at high altitudes volemia increases by increasing globular volume (altitude
polycytemia)
– high temperature induces volemia decrease by dehydr ation
• changes in posture
– after 30 minutes of standing in orthostatic positio n, volemia decreases by
approximately 15% due to increased capillary hydros tatic pressure of the lower limbs
– short time supine position slightly increases volem ia
– long time supine position decreases volemia

PATHOLOGIC VARIATIONS
• Hypovolemia represents decrease of total blood volume under no rmal values. Causes:
– CV decrease – in anemia
– PV decrease – in dehydration (severe vomiting and d iarrhea, burns)
– PV and CV decrease – in hemorrhages
• Hypervolemia represents increase of total blood volume above no rmal values. Causes:
– CV increase- in polycytemia (high altitude, polycyt emia vera)
– PV increase – in hyperaldosteronism
– PV and CV increase – in hyperthyroidism, leukemia

2. ELECTROLYTE BALANCE

ISOIONIA . Represents maintenance of the plasma ions’ concentration between normal
ranges. Electrolyte balances could be evaluated usi ng blood testing and urinary testing.

PLASMA ELECTROLYTES. Represents the quantitative evaluation of main ions
concentration in plasma.

Table I. Electrolytes concentration in plasma (after Harris on 2001).
Cations mEq/l mOsm/l
Na + 136-145 136-145
K + 3.5-5 3.5-5
Ca 2+ 2.2-2.8 1.1-1.4
Mg 2+ 1.6-2.4 0.8-1.2
Total cations 155
Anions mEq/l mOsm/l
Cl – 98-106 98-106
HCO 3 –
23-27 23-27
HPO 4 2- 1.9-2.9 1
SO 4 2- 1 0.5
RCOO – 6 6
Proteins – 16 2
Total anions 155

Concentration change of various ions defines dyselectrolytemia . For example: decreased
plasma K+ concentration (<3.5 mEq/l) is called hypokalemia, and can occur through the
digestive or kidney loss, in hyperaldosteronism, et c. Increased plasma K+ concentration (>5.5
mEq/l) is called hyperkalemia and appears in renal failure, hypoaldosteronism, etc.

Practical Laboratories Physiology I
5 Table II. Pathologic changes of plasma concentration of elec trolytes.
Electrolytes Vomiting Diarrhea Hyper-ALDO Hypo-PTH
Na + ↓ ↓ ↑ N
K + ↓ ↓ ↓ N
Ca 2+ N N N ↓
Mg 2+ N N N ↓
Cl – ↓ ↓ ↑ N
HCO 3 –
↑ ↓ ↑ N
HPO 4 2- N N N ↑
SO 4 2- N N N N
RCOO – N N N N
Proteins – N N N N
Legend: ALDO = aldosteron, PTH = parathyroid hormon e

URINE ELECTROLYTES . Represents the quantitative evaluation of concentra tion (mEq/l)
of the most important ions in urine. The concentrat ion of urinary electrolytes varies in very
wide ranges in order to maintain normal values of p lasma electrolytes.

Table III. Normal electrolytes concentration in urine.
Electrolytes mmol/24 hours
Na + 40-220
K + 25-125
Ca 2+ 2.5-7.5
Mg 2+ 3-5
Cl – 140-250
HCO 3 –
0-3
HPO 4 2- 15-30
SO 4 2- –
RCOO – –
Proteins – 0

3. DISORDERS OF FLUID AND ELECTROLYTES BALANCE

There are two types of hydro-electrolyte disturbanc es: dehydration and hyperhydration,
revealed by humoral plasma changes, schematized in Tables IV and V.

Table III . Types of extracellular dehydration.
Classification Mechanism Causes Humoral changes
Isotonic
dehydration – proportional loss
of water and
electrolytes
(especially Na +) – loss of blood
and plasma → normal osmolarity
→ Na + normal
→ signs of hemoconcentration
(Ht ↑, proteins ↑)
Hypotonic
dehydration – loss of electrolytes
deeper than water
loss – loss of
digestive fluids
– loss of renal
Na + → osmolarity ↓
→ Na + ↓
→ signs of hemoconcentration
(Ht ↑, proteins ↑)
Hypertonic
dehydration – water loss greater
than that of
electrolytes – insufficient
fluid intake
– skin and kidney
fluid loss → osmolarity ↑
→ Na + ↑
→ signs of haemoconcentration
(Ht ↑, proteins ↑)

Practical Laboratories Physiology I
6 If water losses are greater than those of sodium it produces an extracellular hypertonic
dehydration, which will favor water out of cells, followed by intracellular dehydration .
Association between the intracellular and extracell ular cell defines global dehydration . The
most common causes of global dehydration are digest ive loss and sweat.
In situations which are inducing water and sodium l oss, and in which an incorrectly applied
therapy helped an excess fluid load, extracellular hypotonic dehydration is accompanied by
cellular hyperhydration.

Table V . Types of extracellular hyperhydration.
Classification Mechanism Causes Humoral changes
Isotonic
hyperhydration – simultaneous
water and
electrolyte
retention which
causes edema – hydrostatic pressure ↑
– ↓ colloid-osmotic
pressure
– reduction of lymphatic
drainage – normal osmolarity
– Na + normal
– signs of
haemodilution
(Ht ↓, proteins ↓)
Hypotonic
hyperhydration – predominantly
fluid retention – ingestion of large
quantities of liquids
– prohibition of salt
intake associated with
fluid overload → osmolality ↓
→ Na + ↓
→ signs of
haemodilution
(Ht ↓, proteins ↓)
Hypertonic
hyperhydration – predominantly
sodium retention – hypertonic fluid
infusions
– seawater intake
– corticosteroid therapy →↑ osmolarity
→ Na + ↑
→ signs of
haemodilution
(Ht ↓, proteins ↓)

If the accumulation of water is greater than sodium retention, extracellular hypotonic
hyperhydration will determinate water to enter into the cells, fo llowed by a cellular
hyperhydration . Association between the intracellular and extrace llular hyperhydration
defines global hyperhydration .

EVALUATION OF BODY HYDRATION STATE is performed using:
• measurement of blood pressure (BP low in dehydratio n)
• clinical examination (sockets sunken eyes, dry tong ue, and absence of skin turgor in
dehydration)
• measurement of body weight (decreases in dehydratio n, being especially useful in
children)

INTERPRETATION BULLETINS

1. Interpret the following plasma ionogram (female person, 52 year-old):
Na + = 140 mEq/l
K+ = 4 mEq/l
Ca 2+ = 2 mEq/l
Mg 2+ = 1 mEq/l
Cl – = 102 mEq/l
HCO 3- = 26 mEq/l
HPO 42- = 3.5 mEq/l
SO 42- = 1 mEq/l
RCOO – = 6 mEq/l
Proteins – = 16 mEq/l

Practical Laboratories Physiology I
7 2. Interpret the following plasma ionogram (female person, 47 year-old):
Na + = 150 mEq/l
K+ = 3 mEq/l
Ca 2+ = 2.5 mEq/l
Mg 2+ = 1.8 mEq/l
Cl – = 115 mEq/l
HCO 3- = 30 mEq/l
HPO 42- = 2 mEq/l
SO 42- = 1 mEq/l
RCOO – = 6 mEq/l
Proteins – = 16 mEq/l

3. Interpret the following plasma ionogram (male pe rson, 33 year-old):
Na + = 90 mEq/l
K+ = 3 mEq/l
Ca 2+ = 3.5 mEq/l
Mg 2+ = 2.4 mEq/l
Cl – = 85 mEq/l
HCO 3- = 20 mEq/l
HPO 42- = 2 mEq/l
SO 42- = 1 mEq/l
RCOO – = 6 mEq/l
Proteins – = 16 mEq/l

4. Please to interpret the following plasma ionogra m (female person, 20 year-old):
Na + = 130 mEq/l
K+ = 2.8 mEq/l
Ca 2+ = 2.6 mEq/l
Mg 2+ = 2.1 mEq/l
Cl – = 90 mEq/l
HCO 3- = 31 mEq/l
HPO 42- = 2 mEq/l
SO 42- = 1 mEq/l
RCOO – = 6 mEq/l
Proteins – = 16 mEq/l

MCQs (ONE CORRECT ANSWER)

1. Intracellular fluid compartment:
A. Represents 40% of body weight
B. It is composed of structural water and the intersti tial fluid compartment
C. Represents 45% of the total water
D. It consists of interstitial and intravascular fluid compartment

2. Decreased plasma volume can be found in:
A. Burns
B. Hemorrhages
C. Anemia
D. Hyperhydration

Practical Laboratories Physiology I
8 3. Hypervolemia could be induced by the following cond itions:
A. Hyperhydration
B. Polycythemia
C. Leukemia
D. All these statements are true

4. Isotonic dehydration represents:
A. Loss of water and electrolytes equal
B. Loss of electrolyte greater than the loss of water
C. Loss of water greater than the loss of electrolytes
D. Predominantly fluid retention

5. Hypotonic hyperhydration represents:
A. Equal retention of water and electrolytes
B. Fluid retention predominantly
C. Predominant sodium retention
D. All these statements are true

6. Isotonic hyperhydration is characterized by:
A. Simultaneous retention of water and electrolytes th at cause edema
B. Predominant fluid retention
C. Predominant sodium retention
D. All these statements are true

7. Assessment of body hydration status is made by:
A. Blood pressure measurement
B. Clinical examination
C. Measurement of body weight
D. All these statements are true

8. Hypertonic dehydration is characterized by:
A. Proportionate loss of water and electrolytes (espec ially Na +)
B. Loss of water greater than that of electrolytes
C. Loss of electrolytes more pronounced than the loss of water
D. All these statements are false

9. Humoral changes in isotonic hyperhydration are:
A. Normal osmolarity, Na + normal, signs of haemodilution
B. Osmolarity ↓, ↓ Na +, signs of haemodilution
C. ↑ osmolarity, Na + ↑, signs of haemodilution
D. All these statements are false

10. In hypotonic hyperdration humoral changes are:
A. Normal osmolarity, Na + normal signs of haemodilution
B. Osmolarity ↓, ↓ Na +, signs of haemodilution
C. ↑ osmolarity, Na + ↑, signs of haemodilution
D. All these statements are false

Answers : 1-A, 2-D, 3-D, 4-A, 5-B, 6-A, 7-D, 8-B, 9-A, 10-B.