Download MBBS Water and Electrolyte Balance Lecture PPT

WATER AND ELECTROLYTE

BALANCE
Role of water

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Water is a medium for a vast number of biochemical

reactions that occur each moment, which form the

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basis of life

Water solubilises various biomolecules such as

proteins, nucleic acid and carbohydrates by forming

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hydrogen bond with them

Apart from providing an aqueous medium, water act

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as strong nucleophile,directly participates as reactant

in various metabolic reaction

Water plays an important role in regulating body

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temperature


ELECTROLYTE ? DISTRIBUTION AND

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BALANCE

Electrolytes are the substances which readily

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dissociate in solution and exist in ionic form i.e.

positively and negatively charged ions

Electrolytes are well distributed in body fluids to

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maintain osmotic equilibrium and water balance

Sodium is the principal cation of ECF,while potassium

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is the chief cation of ICF

Chloride and bicarbonate are the principal anion of

ECF,while phosphate is the chief anion of ICF

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The total concentration of cations and anions in each body

compartment is equal in order to maintain electrical

neutrality

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The concentration of molecules in body fluids are mainly

expressed in terms of osmolality and osmolarity

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Osmolality : osmotic pressure exerted by number of moles

per kg of solvent

Osmolarity :osmotic pressure exerted by number of moles

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per litre of solution

The osmolality of plasma is in the range of 280-

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300mosmo/kg

Sodium and its associated anions makes the

largest contribution to plasma osmolality

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It is measured by osmometer

osmolality = 2(Na+)+2(K+)+(glucose)+(urea)
Regulation of water and electrolyte

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balance

Kidney play a major role in the regulation of

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electrolyte and water balance

The regulation is maintained by the hormones

aldosterone,ADH and renin-angiotensin

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Aldosterone is a mineralcorticoid produced by the

zona glomerulosa of the adrenal cortex in response to

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angiotensin II derived by the action of renin
Renin-Angiotensin system
The secretion of aldosterone is regulated by the renin-

angiotensin system

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When there is fall in ECF volume, renal plasma flow

decreases and this would be sensed by the

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juxtaglomerular apparatus of the nephron which

secrete renin

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Hyponatremia

Hyponatremia is defined as decrease plasma sodium

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concentration below 136 meq/l

Hyponatremia typically manifests itself clinically as

nausea,genarlized weakness and mental confusion at

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value below 120 meq/l

The central nervous system symptoms are primarily

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caused by movement of water in to cells to maintain

osomotic balance and thus swelling of CNS cells

Hyposmotic Hyponatremia

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Hyperosmotic Hyponatremia
Isosmotic Hyponatremia
Hyposmotic Hyponatremia

This type of hyponatremia can be result of either

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excess loss of sodium (depletional hyponatremia) or

increased ECF volume (dilutional hyponatremia)

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Differentiating these initially requires a clinical

assessment of TBW and ECF volume

Depletional hyponatremia is almost accompanied by a

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loss of ECF water, but to a lesser extent than sodium

loss

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Dilutional hyponatremia is a result

of excess water retention and can

often be detected during physical

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examination as presence of weight

gain or edema

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Hyperosmotic Hyponatremia

Hyponatremia occurs with an increased amount of

other solutes in the ECF,causing an extracellular shift

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of water or intracellular shift of sodium to maintain

osmotic balance between ECF and ICF

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The most common cause of this type of hyponatremia

is severe hyperglycemia

As a general rule,the Na+decreases by 1.6 mmoles/l

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for every 100 mg/dl increase of glucose above 100

mg/dl

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The clinical use of mannitol for osmotic diuresis can

have similar effect
Isosmotic Hyponatremia

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If the measured sodium concentration in plasma is

decreased,but measured plasma

osmolality,glucose,urea are normal ,the only

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explanation is pseudohyponatremia

This occurs when sodium is measured by an

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indirect ion selective electrode in patient with

severe hyperlipidemia or in state of

hyperproteinemia caused due to multiple

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myeloma
Hypernatremia

Hypernatremia (plasma Na+>150mmol/l) is always

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hyperosmolar

Symptoms of hypernatremia is primarly neurological

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and include tremors,irratibility,ataxia,confusion and

coma

Most cases of hypernatremia occurs in patients with

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altered mental status or infants,both of whom may

have difficulty in rehydrating themselves despite a

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normal thirst reflex


Hypovolemic Hypernatremia

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Normovolemic Hypernatremia

Hypervolemic Hypernatremia

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Hypokalemia

Plasma potassium level less than 3.5 meq/l is called

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hypokalemia

Characterized by muscle weakness,irratibility and

paralysis

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Plasma potassium less than 3 meq/l are associated

with serious neuromuscular symptoms

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Tachycardia along with flattened T waves is seen in

ECG

Caused due to redistribution of ECF k+ in to ICF or due

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to true k+ deficit(loss of potassium rich body fluid or

decreased intake of k+ )
Redistribution

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Insulin therapy for diabetic hyperglycemia
Metabolic alkalosis
Acute leukemia

True potassium deficit

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Extrarenal loss in diarrhea or excessive sweating
Renal loss in acute tubular necrosis
Mineralcorticoid excess
Cushing syndrome
Hyperkalemia

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Plasma potassium greater than 5 mmoles/l is called

hyperkalemia

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Characterized by mental

confusion,weakness,tingling,flaccid paralysis of the

extremities

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Cardiac effects of hyperkalemia including bradycardia and

conduction defect evident on ECG by prolonged PR and

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QRS interval and peaked T waves

Level above 7 mmoles/l leads to cardiac arrest
Pseudohyperkalemia
Hemolysis

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Thrombocytosis(>106/l)
Leukocytosis(>105/l)

Redistribution
Metabolic acidosis

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Dehydration
Massive tissue hypoxia
Insulin deficiency
Potassium retention
Acute renal disease and end stage renal failure

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Addison disease

ACE inhibitors

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Potassiun sparing diuretics (spironolactone,Amiloride)