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

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

Electrolyte

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

Solute Overview: Intracellular vs. Extracellular

Ionic composition very different Total ionic concentration very similar

METHODS OF FLUID & ELECTROLYTE MOVEMENT

Diffusion Osmosis Active

Transport

Electrolyte Functions

Controlling fluids movements between compartments

The movement of fluids across cell membrane differs from the movement of fluids between interstitial compartment and plasma

Fluid Movements across cell membrane

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.

Fluid movement between ISF and Plasma

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 135-146 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

Sodium Regulation

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

Mechanism of Na+ Selective Reabsorption in Collecting Duct

Mechanism of Na+ Selective Reabsorption in Collecting Duct