Role of Sodium and General Mineral Functions
Minerals such as sodium, potassium, calcium, phosphorus, copper, and iron participate in metabolism, form tissue structures, and maintain homeostasis. Among them, sodium (Na+) and potassium are of key importance.
- Sodium acts as the major cation of blood plasma.
- Normal values range from 135–155 mmol/L.
- Its primary physiological function is determining the osmotic pressure of the blood.
Sodium metabolism disorders manifest as hyponatremia and hypernatremia.
Physiology and Regulation of Potassium Metabolism
Potassium performs vital functions in the body:
- Participates in protein and glycogen synthesis.
- Affects acid-base balance.
- Ensures the excitation process via Na+ influx into the cell and K+ efflux from the cell.
The extracellular potassium concentration in plasma is 3.6–5.0 mmol/L, which does not significantly affect extracellular fluid osmolarity. The main route of excretion is the kidneys, with a smaller fraction excreted via sweat glands and the gastrointestinal tract. Complete potassium reabsorption occurs in the proximal tubules, while secretion in exchange for sodium occurs in the distal tubules.
An important role is played by the mineralocorticoid aldosterone, which promotes sodium retention and the excretion of potassium and hydrogen ions (known as Berliner's law).
Hypokalemia: Etiology and Pathogenesis
A decrease in blood potassium levels is caused by several groups of factors:
- Decreased dietary intake.
- Body loss through the gastrointestinal tract (vomiting, diarrhea, colon tumors, malabsorption) and kidneys.
- Drug-induced causes — use of carbonic anhydrase-blocking diuretics (hydrochlorothiazide, dichlorphenamide), which cause polyuria, kaliuresis, and urine alkalinization.
- Endocrine disorders (hyperaldosteronism).
- Pathological conditions: heart, liver, and kidney diseases, stress, pheochromocytoma, and neurogenic anorexia.
Redistributive pathogenesis includes metabolic alkalosis (decrease in plasma K+) and insulin therapy, which binds potassium during enhanced glycogen and protein synthesis.
Features of Copper Metabolism
Copper is distributed unevenly in tissues: its total amount is small, but it is relatively abundant in hepatocytes.
- Transport: carried out in blood plasma in the form of ceruloplasmin.
- Balance: micronutrient intake is strictly balanced by its excretion, which occurs mainly via bile.
- Diagnostics: to detect copper in tissues, the special Okamoto method, based on the use of rubeanic acid, is applied.