ELECTROLYTES

Electrolytes
Electrolytes are chemical substances that separate, when dissolved in fluids, into electrically charged particles (ions) capable of conducting electric currents which is vital for the function of nerves and muscles. Any of various ions, such as sodium, potassium, or chloride, required by cells to regulate the electric charge and flow of water molecules across the cell membrane are called electrolytes. Electrolytes are composed of positively charged species, called cations, and negatively charged species, called anions. For example, sodium chloride (NaCl) is an electrolyte composed of sodium cations (Na+) and chlorine anions (Cl−). The ratio of cations to anions is always such that the substance is electrically neutral.
Any substance that produces ions when dissolved is an electrolyte. These substances include ionic materials composed of simple monatomic ions, such as sodium chloride, or substances composed of polyatomic ions, such as ammonium nitrate (NH4NO3). When these substances are dissolved, hydrated ions are generated, as in reactions (1) and (2).
(1)

(2)


Extracellular Fluid:
The term Extracellular fluid includes both interstitial & vasecular fluids. Extracellular fluid also includes with plasma, cerebrospinal fluid, lymph, peritoneal, plural & synovial fluid. About 40% of the interstitial fluid(4 liters) is constituted of dense connective tissues such as bone & cartilage & does not take part in quick exchange with the remaining body fluid.
The active part of this fluid is comprised with interstitial fluid(6.5 liters) & plasma (3.5 liters).
In other words the Extracellular fluid is a compartment containing a heterogeneous collection of fluid & not a continuous fluid phase

In 1959 Edelman & Leibman have studied thoroughly the distribution pattern of body water by dilution technique & also by tissue analysis. It is postulated that 55% of water is present in the Extracellular space. The extracelluler fluid phase can be diluted into following sub-compartment
1. Transcellular water-2.5%
2. dense connective tissue & cartilage water-7.5%
3. Plasma water that contained with



Intracellular fluid:
It is neither a continuous nor a homogenous phase & represents the sum of the fluid contents of all the cells of the body. In a cell there are many anatomic subdivision & for this reason there is a striking difference in water content & ionic composition in between the cytoplasm, nucleus, mitochondria & microsomes of various cell types. This intercellular fluid contains about 30-40% of the body weight & holds about 55% of the whole body water.

Review normal body water distribution
• 1 gm = 1 ml; 1 kg = 1 liter; 1 kg = 2.2 lbs
• Total body water: 60% of body weight
• Intracellular water: 40% of body weight
• Extracellular water (plasma water + interstitial water): 20% of body weight
• Interstitial water: 15 % of body weight
• Plasma water: 5 % of body weight
• Blood volume: 9 % of body weight (blood volume = plasma water + red blood cell volume)
• Inter-compartmental distribution of water is maintained by hydrostatic, oncotic, and osmotic forces
• Daily water requirement: 1-3 ml/kg/hr (24-72 ml/kg/day)
• 50 ml x body weight (kg) provides rough estimate for daily requirement
• Requirements vary with age, environment, disease, etc…