Water & Electrolyte Balance

 

water & electrolyte balance

Water is the major component of our body. It represents large portion of body’s mass.

 

•     Men: 57-65% of total body weight.

•     Women: 46-53% total body weight.

•     Neonate:75% of the body weight is water.

•     Due to differences in Body Composition, muscle has higher hydration level than fat tissue.

water

Two main “Water Compartments”:

•     Intracellular fluid (ICF)….{2/3}.

•     Extra cellular fluid (ECF)….{1/3 }.

§ Plasma.

§ Interstitial fluid.

§ Lymph.

§ Gut.

§ CSF&  Urine.

§  INTRACELLULAR FLUID (ICF)

§  Inside cell.

§  Most of body fluid here - 40% weight.

§  Decreased in elderly.

§  EXTRACELLULAR FLUID (ECF)

§  Outside cell ,it can present either in :

1-Intravascular fluid - within blood vessels.

2-Interstitial fluid - between cells & blood vessels .

3-Transcellular fluid - cerebrospinal, pericardial , synovial .

 

 

§  Importance  of body water

§   Water is an Essential Nutrient
next only in importance to Oxygen.

§  Loss of water even for a few days can lead to death.

§   Serves as Body’s transport medium

•      Gas diffusion .

•      Nutrient transport .

•      Waste disposal.

•      Heat dissipation.

•      Joint lubrication.

•      Provides “physique” for cell structure.

•     It is a constituent of all body fluids

 

 

§  Water  balance

§   Normally about 2.5 L of fluid intake required\day.

§   Water obtained from three sources:

 Liquid, food, & metabolism.

Water intake:

§   Normal = 1200 ml/day.

•      (­ 6X w/ exercise)

§   Food = 1000 ml /day.

§   Metabolism = 350 ml / day.

•      Up to 25% of water requirement.

•      Combination of H+ and O^2- as end result of metabolism.

 

§   Water output

§  Urine: (95% H₂O) 1500 ml/day

•     ­ w/ high protein diets

§  Skin: Evaporative cooling; 700 ml / day (­ drastically w/ ex.)

§  Water Vapor: Exhaled air; 350 ml/day (Varies w/ climate & ex.)

§  Feces: 200 ml/day (may  significantly w/ illness)

 

§  Water requirement

§  About 1 ml of water is needed per 1 kcal energy intake , thus about 2000 ml water is necessary when energy intake is 2000.

§  Infants who have a large body surface area , in proportion to body weight ,need 1.5 ml water / 1 kcal energy intake.

§  The amount of water needed by an individual depend on:

Environmental temp. ,humidity ,occupation & diet.

§  Regulation of body water

§  ADH – antidiuretic hormone + thirst

•     Decreased amount of water in body.

•     Increased amount of Na+ in the body.

•     Increased blood osmolality.

•     Decreased circulating blood volume.

§  Stimulate osmoreceptors in hypothalamus
ADH released from posterior pituitary increased
 thirst.

 

§  Result:
  * Increased water consumption.
  * Increased water conservation.

          * Increased water in body.

        * Increased volume of circulating blood.

        * Decreased Na+ concentration.

 

§  Electrolytes

 

§  Salt that dissociates in solution into electrically charged particles (ions).

•    Cations - positive charge.

•    Anions - negative charge.

§  Function in fluid balance, help maintain acid-base balance ,transmission of nerve impulses, and muscular activity.

§  Electrolytes means that carry electrical current and it can dissolves in body fluids.

 

 

 

§  Strong Ions

§  Cations                    

•     Na⁺

•     K⁺                  

•     Ca²⁺

•     Mg²⁺

§  Anions

•     Cl^-

•     SO₄^2-

•     PO₄²

•     HCO3--

§  Electrolytes

§  Na+, K+, Cl-

•     K+ is ICF predominate cation.

•     Na+ is ECF predominate cation.

•     determines water distribution between compartments.

 

§  Homeostasis maintained by:

§  Ion transport.

§  Water movement .

§  Kidney function.

§  Fluid and electrolyte by these, homeostasis is maintained in the body.

§  Neutral balance:  input = output

§  Positive balance: input > output

§  Negative balance: input < output

§  Electrolyte balance

§  Na ⁺ (Sodium)

•     90 % of total ECF cations.

•      Normal range:136 -145 mEq / L.

•     Pairs with Cl^- , HCO₃^- to neutralize charge.

•     Low in ICF.

•     Most important ion in regulating water balance.

•     Important in nerve and muscle function.

 

§  Regulation of Sodium

§  Renal tubule reabsorption affected by hormones:

•     Aldosterone.

•     Renin/angiotensin.

•     Atrial Natriuretic Peptide (ANP).

 

§  Potassium

§  Major intracellular cation.

§  ICF conc. = 150- 160 mEq/ L.

§  Resting membrane potential.

§  Regulates fluid, ion balance inside cell.

§  pH balance.

§  Normal range(3.5-5.2 mEq/L)

Regulation of Potassium

§  Through kidney:

•     Aldosterone

•     Insulin.

 

 

 

§  Chloride (Cl-)

§  Chloride ions are the major anions of the ECF.  They play a role in regulating osmotic pressure and forming HCl in gastric juice.  Cl^- level is controlled indirectly by ADH and by process that increase or decrease renal absorption of Na⁺.

Bicarbonate ion (HCO₃^- )

§  Bicarbonate ions (HCO₃^- )are the second most abundant anions in the ECF.  Most important buffer in the plasma.

 

§   Calcium

   is the most abundant mineral in the body.  Calcium salts are structural components of bones and teeth.  Ca⁺² which are primarily extracellular cations, function in blood clotting, neurotransmitter release, and contraction of muscle.

   Ca⁺² level is controlled by parathyroid and calcitrol.

 

§  Water imbalance
Dehydration!!!!

§  Water isn’t replaced in body.

§  Fluid shifts from cells to EC space.

§  Cells lose water.

§  Happens in confused, comatose, bedridden persons along with infants & elderly.

§  May be treated with hypotonic sol (like dextrose 5% in water).

 

§  FLUID VOLUME DEFICIT

§  Hypovolemia or FVD is result of water & electrolyte loss .

§  Compensatory mechanisms include:            Increased sympathetic nervous system stimulation with an increase in heart rate & cardiac contraction; thirst; plus release of ADH & aldosterone.

§  Severe case may result in hypovolemic shock or prolonged case may cause renal failure.

 

 

§  CAUSES OF FVD

§  Abnormal GI fluid loss such as  drainage of GI tract.

§  Abnormal fluid loss from skin such as high temperature or burns.

§  Increased water vapor from the lungs such as hyperventilation, fever and high attitude.

§  Conditions that increase renal excretion of fluids such as diuretics & hypersomolar tube feedings.

§  Decrease in fluid intake.

§  Third-space shift such as ascites or trauma.

 

 

§  Water Intoxication !!!!

§  Excess fluid moves from EC space to IC space.

§  Happens with SIADH,   rapid infusion of hypotonic IV sol or tap water as NG irrigant or enemas; can happen with psychogenic polydipsia ( may drink 12-18 L/day ).

§  Findings  Serum Na+ < 125 mEq/L                   Serum Osmolality < 280 mOsm/kg

 

 

§  Electrolyte imbalances

§  Sodium(Normal range 135-145mEq /L).

§   Hypernatremia (high levels of sodium)

•     Plasma Na+ > 145 mEq / L.

•     Due to ↑ Na + or ↓ water.

•     Water moves from ICF → ECF.

•     Cells dehydrate.

§   Hypernatremia Due to:

•     Hypertonic IV soln.

•     Over secretion of aldosterone.

 

§  To be continue…
causes of hypernatremia

•     Loss of pure water

§ Long term sweating with chronic fever.

§ Respiratory infection → water vapor loss.

§ Diabetes – polyuria.

•     Insufficient intake of water (hypodipsia).

 

§  Hyponatremia

§  Overall decrease in Na+ in ECF.

§  Two types: depletional and dilutional.

§  Depletional Hyponatremia.

Na+ loss:

•      diuretics, chronic vomiting.

•      Chronic diarrhea.

•      Decreased aldosterone.

•      Decreased Na+ intake.

 

§  Dilutional Hyponatremia:

•      Renal dysfunction with ↑  intake of hypotonic fluids.

•      Excessive sweating→ increased thirst → intake of excessive amounts of pure water.

•      Syndrome of Inappropriate ADH (SIADH) or oliguric renal failure, severe congestive heart failure, cirrhosis all lead to:

§ Impaired renal excretion of water

•     Hyperglycemia – attracts water.

 

 

§  Potassium: (Normal range 3.5- 5.2 mEq / L)
 Hypokalemia

§  Serum K⁺ < 3.5 mEq /L

§  Beware if diabetic

•     Insulin gets K⁺ into cell.

•     Ketoacidosis – H⁺ replaces K⁺, which is lost in urine.

§  β – adrenergic drugs or epinephrine.

§   Causes of Hypokalemia

^§     Decreased intake of K⁺

§  Increased K⁺ loss

•     Chronic diuretics.

•     Acid/base imbalance.

•     Trauma and stress.

•     Increased aldosterone.

•     Redistribution between ICF and ECF .

 

§   Hyperkalemia

§   Serum K+ > 5.5 mEq / L

§   Check for renal disease.

§   Massive cellular trauma.

§   Insulin deficiency.

§   Addison’s disease .

§   Potassium sparing diuretics.

§   Decreased blood pH.

§   Exercise causes K+ to move out of cells.

§  Calcium Imbalances

 

§  Hypercalcemia

§  Results from:

•      Hyperparathyroidism .

•      Renal disease.

•      Excessive intake of vitamin D.

•      Malignant tumors – hypercalcemia of malignancy

§ Tumor products promote bone breakdown

 

§  Hypercalcemia

§   Usually also see hypophosphatemia

§   Effects:

•       Many nonspecific – fatigue, weakness, lethargy.

•       Increases formation of kidney stones and pancreatic stones.

•       Muscle cramps.

•       Bradycardia, cardiac arrest (systole).

•       Pain.

•       GI activity also common

§  Nausea, abdominal cramps

§  Diarrhea / constipation

•       Metastatic calcification.

§  Hypocalcemia

§  Hyperactive neuromuscular reflexes and tetany differentiate it from hypercalcemia.

§  Convulsions in severe cases.

§  Caused by:

•      Renal failure.

•      Lack of vitamin D.

•      Suppression of parathyroid function.

•      Hyper secretion of calcitonin.

•      Malabsorption states.

•      Abnormal intestinal acidity and acid/ base bal.

•      Widespread infection or peritoneal inflammation

 

 

 

 

 

 

 

References

 

1. Austgen, L; Bowen, R.A; Rouge, M. Path physiology of the digestive system. Colorado State University. 2001. http:/arbl.cvmbs.colostate.edu/hbooks.

2. Casiday, R; Frey, R. Blood, sweat and buffers: pH regulation during exercise. Washington University, Department of Chemistry.2001.http://wunmr.wustl.edu/EduDev/LabTutorials/blood.htm.

3. Casiday, R; Frey R. Maintaining the body’s chemistry: dialysis in the kidneys, Washington University, Department of Chemistry.2001.http://wunmr.wustl.edu/EduDev/LabTutorials/blood.