Fluid and Electrolyte Balance
Hawler Medical University
College of Medicine
Department of Basic Science/Biochemi
2nd year Medical Students
Prepared by
Fargeen. E. Abdullah
M. Sc. in Clinical Biochemistry,
(Email: fargeen.ezzaddin@hmu.edu.krd)
Introduction:
o Water is the most important nutrient for life.
o It constitutes 55-60% of the total body weight.
o The body water is distributed between two
compartments, extracellular fluid(ECF) and
intracellular fluid(ICF).
o The ECF is further divided into blood plasma with
blood vessels, and interstitial fluid.
o Approximately 2/3 rd of body fluid is IC and 1/3 is
EC.
Functions of Body Fluid:
1. Medium for transport.
2. Needed for cellular metabolism.
3. Solvent for electrolytes and other constituents.
4. Helps maintain body temperature.
5. Helps digestion and elimination.
6. Acts as lubricant.
Mechanisms of Fluid Gain and Loss
Gain Loss
o Fluid intake 1700- o Urine 1000-1500ml
2000ml o Sweat 400ml
o Water produced by o Respiration 400ml
metabolism 300-500ml o Faeces 200ml
Total 2000-2500ml Total 2000-2500ml
Regulation of Fluids:
o Hypothalamus –thirst receptors
continuosly monitor serum osmolarity. If it rises,
thirst mechanism is triggered.
o Pituitary regulation- posterior pituitary releases
ADH (antidiuretic hormone) in response to
increasing serum osmolarity. Causes renal tubules
to retain H20.
Regulation of Fluids, cont.
o Renal regulation- by secreting Renin.
Renin: Angiotensin I → Angiotensin II
Angiotensin II causes Na and H20 retention by
kidneys.
o Adrenal Cortex secretes Aldosterone
which causes kidneys to excrete K and retain Na
and H20.
Hypovolemia and Hypervolemia
A- Hypovolemia(Dehydration):
o Loss of water from the body in excess amounts
leads to dehydration.
o Plasma becomes concentrated followed by ECF and
later ICF.
o When water comes out of the cells, it also passes
into ECF in exchange of K and Na passes into ICF
from ECF.
oLoss of more than 20% of body water results in
death.
Causes of Hypovolemia:
1- Severe diarrhea and vomiting.
2- Non availability of drinking water as in the case of
desert.
3- Difficulty in swallowing and state of
unconciousness.
4- Loss of fluid from skin in case of burns.
5- Diabetes insipidus(↓ADH, polyurea).
6- Heart stroke.
7- Excitement.
Features of Hypovolemia:
- Drynessof skin, tongue, throat.
- Changes in the value of packed cell volume, Hb,
plasma protein, plasma electrolytes, urea and
decreased blood pressure.
Treatment:
- Consuming plenty of plain water or water
containing sugar and salt. If the condition is very
severe, intravenous infusion of fluids(normal
saline) is required.
B- Hypervolemia(Water Excess) :
Causes:
1- Hypersecretion of ADH following the administration of
anaesthetics. This effect takes for about 12-36hr after the
surgery.
2- Renal failure.
3- SIADH (Syndrome of inappropriate ADH secretion).
Features of Hypervolemia:
- Mental confusion, incoordination, muscular
weakness, nausea.
- Decreased PCV.
- Decreased plasma electrolytes, plasma osmolality,
increased urine osmolality and increased blood
pressure.
Treatment:
- Withdrawal of fluids.
- Administration of diuretics.
Electrolytes
o Work with fluids to keep the body healthy and in
balance.
o They are solutes that are found in various
concentrations and measured in terms of
milliequivalent (mEq) units.
o Can be negatively charged (anions) or positively
charged (cations)
o For homeostasis body needs:
Total body ANIONS = Total body CATIONS
Electrolytes
• Cations • Anions
o Positively charged o Negatively charged
o Chloride Cl-
o Sodium Na+ o Phosphate PO4-
o Potassium K+ o Bicarbonate HCO3-
o Calcium Ca2+
o Magnesium Mg2+
Electrolyte Functions
o Regulate water distribution
o Muscle contraction
o Nerve impulse transmission
o Blood clotting
o Regulate enzyme reactions
o Regulate acid-base balance
Sodium Na+
o The major cation of the ECF.
o Serum Sodium level is (135-145)mEq/L.
o Essential for maintaining normal nerve and muscle
activity (Na/K pump).
o Regulating osmotic pressure.
oPreserving acid-base balance.
o Regulates volume of body fluids.
o Regulated by kidneys/hormones.
Hyponatremia:
o Serum Na+ <135mEq/L.
o Results from excess of water or loss of Na+.
- Loss of Na+ in GI losses; vomiting; diarrhea.
- Dilutional hyponatremia in some medical
conditions; CHF; renal failure; SIADH(cancer,
pituitary trauma); Addison’s
Disease(hypoaldosteronism, Na loss).
Hypernatremia:
o Serum Na+> 145mEq/L.
o Results from Na+ gained in excess of H2O or water
is lost in excess of Na+.
o High fever & Severe dehydration.
o Excessive salt intake without sufficient water intake
o Decreased activity of ADH.
o Diabetes Mellitus(hyperglycemic dehydration).
o Cushing syndrome(Hyperaldosteronism).
Potassium K+
o The major cation of ICF.
o Serum K+ level is (3.5-5mEq/L).
o EC K+ is important for muscle contraction, nerve
and electrical impulse conduction, and operation of
Na+/K+ pump.
o IC K+ is necessary for regulating enzyme activity,
maintaining osmotic and acid- base balance.
o Regulated by kidneys/hormones.
o Inversely proportional to Na.
Hypokalemia:
o Serum level < 3.5mEq/L.
o Results from decreased intake and loss via
GIT/Renal.
- GIT loss like prolonged vomiting; and diarrhea,
renal loss like diuretics.
o certain medical conditions that cause hypokalemia:
- Renal disease/CHF (dilution).
- Metabolic alkalosis.
- Cushing Disease(Na retention leads to K loss).
Hyperkalemia:
o Serum level >5mEq/L
o Results from excess intake.
- IV therapy.
o Transcellular shifts like acidemia, relative insulin
deficiency and cell injury.
o Decreased excretion like in CHF, mineralocorticoid
deficiency(volume depletion), acute and chronic renal
failure and glomerulonephritis.
o Addison’s Disease(Na loss leads to K retention).
Calcium Ca2+
o Serum level is 4.5-5mEq/L.
o Most abundant mineral in the human body.
o The average adult body contains 1-1.4kg, 99% is in
teeth and bones.
o Plasma Ca exists in 3 forms, ionized Ca2+, protein
bounded(albumin), and complex form as(citrate,
phosphate, and bicarbonate).
o needed for nerve transmission, vitamin B12
absorption, muscle contraction & blood clotting.
Hypocalcaemia:
o Serum Ca <4.3mEq/L.
o Results from decreased intake as in
-Vitamin D3 deficiency, lack of sunlight plus poor
nutrition, and malabsorption.
o Decreased plasma albumin as in malnutrition, &
burns.
o Increased renal loss by calcitonin hormone.
oParathyroid disorders.
Hypocalcaemia, cont.
- Decreased flux from bone as in PTH deficiency, &
surgical removal of glands.
- Increased flux into bone “hungry bones” as in
postparathyroidectomy.
o Symptoms of hypocalcaemia: tingling of the finger
tips; abdominal & muscle cramps; tetany; seizures;
osteomalacia; & rickets.
Hypercalcaemia:
o Serum Ca2+ > 5.3mEq/L.
o Results from increased intake/absorption e.g. vitamin
D3.
o Increased plasma albumin as in dehydration.
o Increased bone resorption as in hyperparathyroidism,
& malignancy.
o Increased renal reabsorption as in thiazide diuretics, &
Addison’s disease.
o Symptoms are fatigue, depression, anorexia, muscle
weakness, renal calculi, & cardiac changes.
Chloride Cl-
o The major extracellular anion.
o Serum Cl- level is (95- 105)mEq/L.
o Maintains water balance, and acid-base balance.
o Aids in digestion(HCl), & osmotic pressure(with Na
&H2O).
o Regulated by kidneys.
o Follows Sodium.
Hypochloremia:
Serum level < 95mEq/L.
o
o Results from prolonged vomiting(loss of gastric
HCl).
o Salt-losing renal disease.
o Metabolic acidosis.
Hyperchloremia:
o Serum level > 105mEq/L.
o Results from excessive intake or retention by
kidneys.
o Dehydration.
