water, electrolytes and acid-base balance

1. Water, Electrolyte and
Acid-base Balance

2. Introduction
• Organisms possesses capacity to survive against odds and maintain
homeostasis.
• Maintaining homeostasis is very important for water, electrolyte and
acid-base status of the body.
• Kidney actively participates in the regulation of water, electrolyte and
acid-base balance.

3. WATER AND LIFE
• Water is the solvent of life and it is involved in several body functions.
―It provides the aqueous medium which is essential for the various
biochemical reactions to occur
―Directly participates as a reactant in several metabolic reactions.
― It serves as a vehicle for transport of solutes.
― It is closely associated with the regulation of body temperature.

4. WATER AND LIFE….
• An adult human contains about 60% water (men 55-70%, women 45-
60%).
• A 70 kg normal man contains about 42 liters of water. This is
distributed as
• Intracellular fluid (ICF) 28L
• extracellular fluid (ECF) 14L
• Interstitial fluid 10.5L
• plasma 3.5L

5. WATER TURNOVER AND BALANCE
• The body possesses capacity to regulate its water content
• This regulation is achieved by balancing the daily water intake and
water output

6. WATER TURNOVER AND BALANCE…
• Water is supplied to the body by exogenous and endogenous sources
• Exogenous water are the ingested water, beverages and water
content of solid foods
• Ingestion of water is mainly controlled by a thirst center located in the
hypothalamus.
• Increase in the osmolality of plasma causes increased water intake by
stimulating thirst centre.
• Endogenous water are the metabolic water produced within the
body
• This water (300-350 ml/day) is derived from the oxidation of foodstuffs

7. WATER TURNOVER AND BALANCE…
• Water is removed from the body in four distinct routes:
1. Urine :
• This is the major route for water loss from the body.
• In a healthy individual, the urine output is about 1-2 L/day
• Water excretion by the kidney is controlled by vasopressin also called
antidiuretic hormone (ADH) secreted from posterior pituitary gland.
• ADH secretion leads to an increased water reabsorption from the renal
tubules (less urine output)
• Diabetes insipidus is a disorder characterized by the deficiency of ADH which
results in an increased loss of water from the body

8. WATER TURNOVER AND BALANCE…
• Water is removed from the body in four distinct routes:
2. Skin :
• Loss of water (450 ml/day) occurs through the body surface by
perspiration
3. Lungs :
• During respiration, some amount of water (about 400 ml/day) is lost through
the expired air
4. Feces
• Most of the water entering the gastrointestinal tract is reabsorbed by the
intestine
• About 150 ml/day is lost through feces in a healthy individual
• Fecal loss of water is tremendously increased in diarrhea

9. ELECTROLYTE BALANCE
• Electrolytes are the compounds which readily dissociate in solution
and exist as ions
• The concentration of electrolytes are expressed as milliequivalents
(mEq/l)
• A gram equivalent weight of a compound is defined as its weight in grams
that can combine or displace 1 g of hydrogen
• One gram equivalent weight is equivalent to 1,000 milliequivalents.
The above formula is employed to convert the concentration mg/l to mEq/l.

10. Electrolyte composition of body fluids
• Electrolytes are well distributed in the body fluids in order to maintain
the osmotic equilibrium and water balance

11. Osmolarity and osmolality of body fluids
• Osmolarity is the number of moles (or millimoles) per liter of solution
• Osmolality is the number of moles (or millimoles) per kg of solvent.
• If the solvent is pure water, there is almost no difference between
osmolarity and osmolality.
• For biological fluids, the osmolality is more commonly used. This is
about 6% greater than osmolarity.

12. Osmolality of plasma, ECF and ICF
• The osmolality of plasma is in the range of
285-295 milliosmoles/kg
• Sodium and its associated anions make the
largest contribution (~90%) to plasma
osmolality.
• Osmolality is generally measured by
osmometer.
• Plasma osmolality can be computed from
the concentrations (mmol/l) of Na+, K+,
urea and glucose as follows

13. Osmolality of plasma, ECF and ICF…
• Movement of water across the biological membranes is dependent on
the osmotic pressure differences between the intracellular fluid (ICF)
and extracellular fluid (ECF).
• In a healthy state, the osmotic pressure of ECF, mainly due to Na+
ions, is equal to the osmotic pressure of ICF which is predominantly
due to K+ ions.

14. Regulation of electrolyte balance
• Electrolyte and water balance are regulated together and the kidneys
play a predominant role in this regard.
• The regulation is mostly achieved through the hormones aldosterone,
ADH and renin-angiotensin

15. Regulation of electrolyte balance…
• Aldosterone :
• produced by adrenal cortex.
• Aldosterone increases Na+ reabsorption by the renal tubules at the expense of K+ and H+
ions.
• Antidiuretic hormone (ADH) :
• An increase in the plasma osmolality stimulates hypothalamus to release ADH.
• ADH increases water reabsorption by renal tubules so it decreases plasma osmolality
• Renin-angiotensin :
• The secretion of aldosterone is controlled by renin-angiotensin system.
• Decrease in the blood pressure is sensed by juxtaglomerular apparatus of the nephron
which secrete renin.
• Renin acts on angiotensinogen to produce angiotensin I.
• Angiotensin converting enzyme (ACE) converts angiotensin I to angiotensin II which
stimulates the release of aldosterone.

16. Regulation of electrolyte balance…
• Atrial natriuretic factor (ANF) or
atriopeptin is a 28-amino acids
containing peptide.
• It is produced in the atrium of heart in
response to increased blood volume,
elevated blood pressure and high salt
intake.
• ANF acts on kidneys to increase GFR,
sodium excretion and urine output.

17. Regulation of electrolyte balance

18. Na+ concentration and ECF
• Na+ and its anions (mainly Cl–) are confined to the extracellular fluid.
• The retention of water in the ECF is directly related to the osmotic
effect of these ions Na+ and Cl–.

19. Dietary intake and electrolyte balance
• The consumption of a well balanced diet supplies the body
requirement of electrolytes.
• Humans do not possess the ability to distinguish between the salt
hunger and water hunger.
• Thirst may regulate electrolyte intake also.
• In hot climates, the loss of electrolyte is usually higher.

20. Dehydration
• Dehydration is a condition characterized by water depletion in the
body.
• It may be due to insufficient intake or excessive water loss or both.
• Dehydration is generally classified into two types.
1. Due to loss of water alone.
2. Due to deprivation of water and electrolytes.
• Dehydration may occur as a result of
• diarrhea, vomiting, excessive sweating, fluid loss in burns, adrenocortical
dysfunction, kidney diseases (e.g. renal insufficiency), deficiency of ADH
(diabetes insipidus) etc
• There are three degrees of dehydration—mild, moderate and severe

21. Dehydration…
• The salient features of dehydration are:
1. The volume of the extracellular fluid is decreased with a concomitant rise in
electrolyte concentration and osmotic pressure.
2. Water is drawn from the intracellular fluid that results in shrunken cells and
disturbed metabolism e.g. increased protein breakdown.
3. ADH secretion is increased. This causes increased water retention in the body
and consequently urine volume is very low.
4. Plasma protein and blood urea concentrations are increased.
5. Water depletion is often accompanied by a loss of electrolytes from the body
(Na+, K+ etc.).
6. The principal clinical symptoms of severe dehydration include increased pulse
rate, low blood pressure, sunken eyeballs, decreased skin turgor, lethargy,
confusion and coma.

22. Dehydration…
• The treatment choice of dehydration is the intake of plenty of water.
• In the subjects who cannot take water orally, it is administered
intravenously in an isotonic solution (usually 5% glucose).
• If the dehydration is accompanied by loss of electrolytes, the same
should be administered by oral or intravenous routes.

23. Osmotic imbalance and dehydration in cholera
• Cholera is transmitted through water and foods, contaminated by the
bacterium Vibrio cholerae.
• This bacterium produces a toxin which stimulates the intestinal cells
to secrete various ions into the intestinal lumen.
• These ions raise the osmotic pressure and suck the water into lumen which
results in diarrhea with a heavy loss of water (5–10 liters/day)
• Oral rehydration therapy (ORT) is commonly used to treat cholera and
other diarrheal diseases

24. Overhydration
• It is also called water intoxication and it is caused by excessive retention of
water in the body.
• This may occur due to excessive intake of large volumes of salt free fluids, renal
failure, overproduction of ADH etc.
• Overhydration is observed after major trauma or operation, lung infections
etc.
• Water intoxication is associated with dilution of ECF and ICF with a
decrease in osmolality.
• The clinical symptoms include headache, lethargy and convulsions.
• The treatment advocated is to stop water intake and administration of
hypertonic saline

25. Water tank model

26. Metabolism of electrolytes
• The body distribution, dietary intake, intestinal absorption and biochemical
functions of individual electrolytes are discussed under the chapter of
mineral metabolism
• Electrolyte disorders, particularly hypernatremia and hyponatremia (of
sodium); hyperkalemia and hypokalemia (of potassium) are also under the
chapter of mineral metabolism
• Diuretics are the drugs that stimulate water and sodium excretion, so that
urine volume is increased
• Examples are diuretics are bendrofluazide, frusemide, spironolactone and mannitol.
• Diuretics are important in the treatment of edema, heart failure and
hypertension

27. ACID-BASE BALANCE
• The normal pH of the blood is maintained in the narrow range of
7.35-7.45.
• Maintenance of blood pH is an important homeostatic mechanism of
the body.
• Changes in blood pH will alter the intracellular pH which, in turn,
influence the metabolism
• The blood pH compatible to life is 6.8-7.8.

28. Production of acids by the body
• The metabolism of the body is accompanied by an overall production
of acids. E.g: carbonic acid, lactic acid, sulfuric acid, phosphoric acid
etc
• A diet rich in animal proteins results in more acid production by the
body and leads to the excretion of urine which is acidic.

29. Production of bases by the body
• The formation of basic compounds in the body, in the normal
circumstances, is negligible.
• Some amount of bicarbonate is generated from the organic acids such
as lactate and citrate.
• A vegetarian diet has a tendency for a net production of bases

30. MAINTENANCE OF BLOOD pH
• There are three ways of regulating the body’s acid-base balance and
maintain the blood pH:
1. Blood buffers
2. Respiratory mechanism
3. Renal mechanism.

31. MAINTENANCE OF BLOOD pH
1. Blood buffers
i. Bicarbonate buffer
ii. Phosphate buffer
iii. Protein buffer.