Electrolyte  Substance when dissolved in solution separates into ions & is able to carry an electrical current  Solute substances dissolved in a solution. These may be electrolytes or non-electrolytes  Electrolytes have an electrical charge when they are dissolved in water  Electrolytes that have a positive charge are called cations  Electrolytes with negative charge are anions

 Cations include sodium (Na+), potassium (K+), calcium (Ca+), Magnesium (Mg+), and hydrogen (H+)  The number of cations must equal the number of anions  The combining power of electrolytes is measured in milliequivalents (mEq)  It is the measure of charge concentration

Anions  Include chloride ions, bicarbonate ions, phoshate ions, sulphate ions, organic acids, and proteins  Measurement of solute concentration in body fluids is based on fluid’s osmotic pressure, expressed as osmolarity  Osmolarity is the number of osmols (standard unit of osmotic pressure) per liter of solution

 Electrolytes are the major components of body fluids. They enter the body through the food we eat and the beverages that we drink.  Electrolytes leave the body by way of urine, skin and feces.  The concentration of electrolyte must be maintained within specific limits

 Ionic composition very different  Total ionic concentration very similar

 Diffusion  Osmosis  Active Transport

 Controlling fluids movements between compartments  The movement of fluids across cell membrane differs from the movement of fluids between interstitial compartment and plasma

 Electrolytes moves across cell membrane through ion channels and ion pumps that are selective for specific ions  Na-K ATPase in the membrane: move ions against their concentration gradients  Channels specific for Na ions allow the ions to diffuse from area of higher concentration to areas of lower concentration  Channels specific for K allows K ions to move across the membrane from areas of higher to lower concentration  Differences in ion concentration between intercellular and intracellular fluids are caused by these selective ion channels

 Water move freely through water channel, which moves from higher water concentration to lower concentration  Through osmosis water moves to the side of membrane of higher solute concentration  Na exerts significant effect on water movements.

 Ions and water can move freely between plasma and ISF  Proteins too big to leave the capillaries  Protein concentration in the plasma is higher than in ISF  Protein in the plasma exerts colloid osmotic pressure. Water moves from ISF to plasma  Capillary hydrostatic pressure forces fluid out of the capillary

Sodium  Major cation in ECF (positively charged)  Responsible for extracellular osmotic pressure  Regulated by Aldosterone and the kidneys  Increases sodium reabsorption in DCT of nephron  Normal serum concentration in ECF ranges from mEq/L

Sodium Functions  Sodium maintains ECF osmolality, ECF volume, and influences water distribution (where salt goes water follows)  It affects the concentration, secretion, and adsorption of potassium  It also help aid the impulse transmission of nerve and muscle fibers

Imbalances  Hyponatremia less than 130 mEq/L)-low sodium level-may cause headache, hypotension, decreased body temp, nausea, vomiting, and possible coma.  Hypernatremia occurs when plasma Na more than 150 mEq/L) -high sodium level-usually indicates water deficit in ECF-symptoms include thirst, dry sticky tongue, confusion, disorientation, hallucination, lethargy, seizures, coma, agitation

 Na is filtered through glomerulus  Na is reabsorbed to plasma at proximal convoluted tubule (PCT) and the loop of Henle  In the presence of Aldosterone, Na reabsorbed at the distal convoluted tubule (DCT)

 Aldosterone: steroid H from adrenal cortex  Stimulates Na + uptake (& K + secretion)   channel synthesis