Water and electrolytes especially sodium are closely associated in their regulation in the body. Both are tightly regulated as a tilt of one may result in serious consequences to an individual.

1. education for health
Department of Chemical Pathology,
FETHA.
Seminar Presentation on:
Regulation of Water and Sodium Balance
By: Dr Onu Emmanuel Mbah
On: 21 Jan. 2016

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Outline
 Introduction
 Body water distribution
 Water Balance
 Control of water and sodium balance
 Regulation of ADH secretion
 Sodium balance
 Osmotic pressure
 SIADH
 Diabetes Insipidus

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Introduction
 Humans have developed complex
physiological systems to maintain the
composition of their internal environment
 Water is an essential constituent of the
human body and homeostatic processes are
important to ensure that the total water
balance is maintained within narrow limits.
 To understand the homeostasis of water in the
human body will be impossible without
incorporatIng electrolyte balance the most
abundant of which is sodium.

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Body water Distribution
 The total body water (TBW) of a 70kg man is
about 42 L contributing about 60% (50% in
females) of the total body weight and
3000mmol of Na+ contributing 92% of the
osmolality of the ECF.
 Approximately two thirds (24 L) of TBW is
distributed into the ICF compartment, and one
third (18 L) exists in the ECF compartment of
which 13 L is interstitial and 5 L is intravascular.
 Within the intravascular compartment, plasma
constitutes 3.5 L for the average adult having
a hematocrit of -40% and a 5-L blood
volume.

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 Activity, environmental conditions, and
disease all have dramatic effects on
daily water (and electrolyte)
requirements.
 On average, an adult must take in 1.5
to 2L of water and 60–150 mmol of Na
daily to maintain balance; in our hot
climate up to 3 L may be required daily.
 Osmotic activity depends on
concentration, and therefore on the
relative amounts of sodium and water in
the ECF compartment, rather than on
the absolute quantity of either

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Water Balance
 Water balance is achieved in the body by
ensuring that the amount of water consumed
in food and drink (and generated by
metabolism) equals the amount of water
excreted in urine, faeces, sweat and expired
air.
 Intake is regulated by behavioral mechanisms,
including thirst and salt cravings.
 The net daily losses amount to about 1.5–2
L of water and 100 mmol of sodium in the
urine, and 100 mL and 15 mmol, respectively,
in the faeces.

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 About 1.7 L of water is lost daily in
sweat and expired air in the tropics
and less than 30 mmol of sodium a
day is lost in sweat.

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Control of water and sodium
balance
 The intake and loss of water and Na are
controlled by:
 Antidiuretic hormone (ADH)
 Renin angiotensin aldosterone mechanism
 Thirst mechanism
 Atrial natriuretic peptide
 ADH causes the insertion of water
channels (aquaphorin 2) into the
membranes of cells lining the collecting
ducts, allowing water reabsorption to occur.

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Regulation of ADH
secretion
 ADH secretion is influenced by several factors
 1. By special receptors in the hypothalamus
that are sensitive to increasing plasma
osmolarity (when the plasma gets too
concentrated). These stimulate ADH secretion.
 2. By stretch receptors in the atria of the heart,
which are activated by a larger than normal
volume of blood returning to the heart from
the veins.
 These inhibit ADH secretion, because the body
wants to rid itself of the excess fluid volume.

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Regulation of ADH
secretion
 3. By stretch receptors in the aorta
and carotid arteries, which are
stimulated when blood pressure falls.
These stimulate ADH secretion.
 4. Stress due to, for example,
nausea, vomiting and pain may also
increase ADH secretion.

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Sodium balance
 The average daily Western diet contains
150–200 mmol of sodium which must be
excreted to avoid volume overload.
 The kidneys are primarily responsible for
excreting the daily sodium load.
 With a normal GFR of 180 L/day,
approximately 27000 mmol of sodium are
filtered at the glomerulus, with less than 1%
of this being excreted in the urine
(approx.150mmol/d)
 The rest of the Na are reabsorbed along the
tubule esp. at proximal part.

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Sodium balance
 The major factors controlling sodium
balance are renal blood flow and
aldosterone.
 Aldosterone controls loss of sodium from
the distal tubule and colon and in sweat &
saliva.
 ANP may cause high sodium excretion
(natriuresis) by increasing the GFR
and by inhibiting renin and aldosterone
secretion.

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Osmotic pressure
 Concentration gradient of particles
across semipermeable membrane
creates osmotic gradient that regulate
movement of particles across the
membrane.
 The osmotic effect of the intravascular
proteins is balanced by very slightly
higher interstitial electrolyte
concentrations - Gibbs–Donnan effect.

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Osmotic pressure
 Water distribution in the body is
dependent largely on three factors, viz:
 1. the number of particles per unit volume
 2. particle size relative to membrane
permeability
 3. concentration gradient across the
membrane.
 Abnormalities of water balance lead to
hyponatraemia or hypernatraemia.

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Syndrome of inappropriate
ADH (SIADH)
 This is a disorder of osmoregulation
where hypotonicity fails to adequately
suppress the production of ADH
resulting in water reabsorption and
further dilution of the plasma.

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Diagnostic criteria for
SIADH
 1. Hyponatraemia (<135 mmol/L)
 2. Decreased serum osmolality (<270
mOsm/kg)
 3. Urine sodium >20 mmol/L
 4. Inappropriate urine concentration
(urine osmolality >100 mOsm/ kg)
 5. Exclusion of renal failure and
endocrine dysfunction

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Causes of SIADH
 .
Carcinomas
Bronchogenic
Gastrointestinal
Bladder Prostate
Pancreas
Drugs, e.g. vincristine,
chlorpropamide,
carbamazepine, non-
steroidal anti-infl
ammatory drugs,
certain
antidepressants,
oxytocin and opiates
Pulmonary
Pneumonia (viral/
bacterial) Tuberculosis
Pulmonary abscess
Aspergillosis
Mesothelioma
Central nervous
system Encephalitis
(viral/bacterial)
Meningitis
(viral/bacterial/TB/
fungal) Brain tumours
Brain abscess
Cerebral haemorrhage

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Recommended therapeutic
strategies
 1. water restriction
 2. increased salt intake with furosemide to
promote renal electrolyte free water
excretion
 3. administration of drugs to antagonise
the action of ADH (e.g. demeclocycline,
conivaptan).
 If the patient is symptomatic with seizures
or a decreased level of consciousness then
the initial treatment should be more rapid
and aim to raise the serum sodium level by
1–2 mmol/L/h over the first 3–4 h.

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Diabetes Insipidus
 Central diabetes insipidus
 Serum ADH levels are low and the
urine osmolality is often markedly low
(50–100 mOsm/kg).
 Nephrogenic diabetes insipidus
 Serum ADH levels are increased but
the urine osmolality remains low (often
50 - 100 mOsm/kg).

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Causes of diabetes
insipidus
 Central DI
 Congenital:
 Autosomal dominant (mutations in
vasopressin precursor) - arginine
vasopressin-neurophysin ll gene.
 Autosomal recessive (Wolfram
syndrome)-wolframin gene mutation -
DIDMOAD

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Causes of diabetes
insipidus
 Central DI
 Acquired:
 Tumours (pituitary, metastases)
 Postsurgery, head trauma
 Infiltration of the pituitary (sarcoid,
histiocytosis)
 CNS infections
 Idiopathic (50%)

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Causes of diabetes
insipidus
 Nephrogenic
 Congenital:
 X-linked (mutations in V2 receptor)
 Autosomal recessive (mutations in aquaporin 2)
 Acquired:
 Chronic renal failure
 Renal interstitial disease (interstitial nephritis,
obstructive uropathy, polycystic kidney disease, lithium
therapy, sickle cell anaemia)
 Electrolyte disorders (hypokalaemia, hypercalcaemia)
 Drugs (lithium, amphotericin, foscarnet)

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Features of DI
 Polydypsia
 Polyuria up to 15 - 20 L/day
 Low urine SG < 1.010
 Low urinary osmolarity
 Urinary Na < 20 mmol/L
 Hypernatremia

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Diagnosis of DI
 Nocturia distinguishes DI from
psychogenic polydypsia.
 Water deprevation test (WDT)
 Principle - the kidneys concentrate
urine to conserve fluid under water
deprivation or scarcity.
 Px is deprived of water and food for
12hrs before the test.

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Precautions in WDT
 Water depravation test should be avoided if:
 1. Hypovolemia
 2. Hypernatraemia
 3. High or high normal plasma osmolality -
300mmol/kg
 4. Px loses >3% of body wt
 5. Px is distressed.
 6. Test should be performed by an
experienced clinician.

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 Urinary osmolality of 750 mmol/kg is
considered adequate urinary
concentration.
 Failure of concentration of three
consecutive urine specimens taken at
hourly intervals indicates either
tubular disease or diabetes insipidus.
 Response to lM 2 µg DDAVP confirms
central DI.

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Treatment of DI
 For CDI - Correct the underlying cause,
DDAVP
 For NDI - Coerrect the underlying
cause, Diuretic or NSAID

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APPRECIATION
Thanks for your Kind Attention