DrX %20(1).png)
DrX Whiz Niraj
Major Extra & Intracellular Electrolytes
Comprehensive exam notes on Physiological Ions, Electrolyte Replacement Therapy (NaCl, KCl, ORS), and Physiological Acid-Base Balance.
Electrolytes are minerals in the body that have an electric charge. They are distributed in two main fluid compartments: Intracellular Fluid (ICF) inside the cells, and Extracellular Fluid (ECF) outside the cells (including blood plasma).
| Ion | Location | Physiological Functions |
|---|---|---|
| Sodium (Na⁺) | Major ECF Cation | Maintains osmotic pressure and fluid balance. Essential for generation of nerve action potentials. |
| Potassium (K⁺) | Major ICF Cation | Maintains resting membrane potential. Crucial for cardiac muscle contraction and rhythm. |
| Calcium (Ca²⁺) | Mostly in Bones | Structural component of bones/teeth. Required for blood clotting, neurotransmitter release, and muscle contraction. |
| Chloride (Cl⁻) | Major ECF Anion | Balances Sodium to maintain osmotic pressure. Essential for forming gastric acid (HCl) in the stomach. |
When the body loses severe amounts of water and electrolytes (due to severe diarrhea, vomiting, or burns), replacement therapy is required to restore normal volume and composition.
Sodium Chloride (NaCl)*
Normal Saline (0.9% w/v) is isotonic with blood plasma.
- Uses: Fluid and electrolyte replenisher in dehydration. Also used as a vehicle for IV drugs.
- Assay: Assayed by Modified Volhard's Method (Precipitation titration using AgNO₃ and NH₄SCN).
Potassium Chloride (KCl)
Used to treat Hypokalemia (low potassium levels), which can occur due to prolonged use of certain diuretics.
- Caution: Must be administered very slowly IV, as rapid infusion can cause cardiac arrest.
Calcium Gluconate*
Less irritating than Calcium Chloride.
- Uses: To treat Hypocalcemia (calcium deficiency) and as a cardiac protector during hyperkalemia.
- Assay: Assayed by Complexometric Titration using standard Disodium EDTA.
ORS is a dry powder containing a mixture of essential electrolytes and carbohydrates. When dissolved in water, it is used to treat severe dehydration (especially caused by cholera or acute diarrhea).
Standard WHO ORS Formula (Reduced Osmolarity):
- Sodium Chloride (NaCl): 2.6 g
- Potassium Chloride (KCl): 1.5 g
- Sodium Citrate: 2.9 g (Acts as an alkalinizing agent to correct acidosis)
- Anhydrous Glucose: 13.5 g
- Total Osmolarity: 245 mOsm/L
Viva Alert: Why add Glucose in ORS?
During severe diarrhea, the normal absorption of Sodium in the intestine fails. However, the Sodium-Glucose Co-transporter (SGLT1) mechanism remains intact. Glucose actively carries Sodium across the intestinal wall. As Sodium enters the blood, water follows passively by osmosis, rapidly rehydrating the patient. Without glucose, ORS would not work effectively!
The normal pH of arterial blood is tightly regulated between 7.35 and 7.45. A drop below 7.35 is called Acidosis, and a rise above 7.45 is called Alkalosis. The body uses Three Lines of Defense to maintain this balance.
| Line of Defense | Mechanism | Speed of Action |
|---|---|---|
| 1. Chemical Buffers | Bicarbonate, Phosphate, and Protein buffers instantly bind to excess H⁺ or OH⁻ to prevent sudden pH changes. | Seconds (Immediate) |
| 2. Respiratory Mechanism | Lungs regulate the amount of Carbon dioxide (CO₂). Increased breathing rate eliminates more CO₂, reducing acidity. | Minutes |
| 3. Renal Mechanism | The kidneys excrete excess H⁺ into the urine and reabsorb/generate new Bicarbonate (HCO₃⁻) back into the blood. | Hours to Days (Slowest but most powerful) |