Summary of Biogenic Elements and Electrolyte Homeostasis
Biogenic Elements & Electrolyte Homeostasis: A Study Guide
Introduction
Electrolytes are charged particles (ions) dissolved in body fluids that maintain osmotic balance, support nerve and muscle function, and participate in acid–base and enzyme-regulated processes. This material summarizes the main electrolytes in body compartments, their roles, common causes and consequences of imbalances, and how imbalances are diagnosed and treated.
Definition: Electrolytes are ions in body fluids that conduct electrical current and regulate physiological processes such as fluid distribution, nerve excitability, and pH balance.
Body fluid compartments and osmolarity
The human body distributes water and solutes among major compartments: intravascular (blood plasma), interstitial (extracellular) fluid, and intracellular fluid. Osmoregulation keeps osmotic pressure balanced across these compartments.
Typical osmolarity and major solutes
Below are average osmolarity values (mmol/L) of representative solutes in body fluids (rounded values as examples):
| Solute | Blood plasma (ECF) | Interstitial fluid (ECF) | Intracellular fluid (ICF) |
|---|---|---|---|
| Na+ | $144$ | $137$ | $10$ |
| K+ | $5$ | $4.7$ | $141$ |
| Ca^{2+} | $2.5$ | $2.4$ | $0$ |
| Mg^{2+} | $1.5$ | $1.4$ | $31$ |
| Cl^- | $107$ | $112.7$ | $4$ |
| HCO_3^- | $27$ | $28.3$ | $10$ |
| HPO_4^{2-} / H_2PO_4^- | $2$ | $2$ | $11$ |
| Proteins (anionic colloids) | $1.2$ | $0.2$ | $4$ |
| Other solutes | $13$ | $13$ | $90.2$ |
| Total osmolarity | $303.7$ | $302.2$ | $302.2$ |
Definition: Osmolarity is the total concentration of osmotically active particles in a solution, expressed in mmol/L.
Main electrolytes and their physiological roles
Electrolytes commonly measured and discussed clinically include: Na+ (sodium), K+ (potassium), Ca^{2+} (calcium), Mg^{2+} (magnesium), Cl^- (chloride), HCO_3^- (bicarbonate), HPO_4^{2-}/H_2PO_4^- (phosphates), SO_4^{2-} (sulfates) and plasma proteins.
- Functions of electrolytes:
- Maintain osmotic pressure and water distribution between compartments
- Maintain acid–base balance (buffer systems)
- Regulate excitability of nerves, heart, and muscles
- Serve as cofactors or activators for enzymes and participate in redox reactions
- Contribute to blood coagulation and membrane stability (e.g., Ca^{2+})
Sodium (Na+)
- Role: Major extracellular cation; primary determinant of ECF osmolarity and volume; important for nerve impulse transmission and cardiac function.
- Reference serum range: $136$–$145\ \mathrm{mmol/L}$.
- Important clinical note: Plasma sodium concentration reflects the ratio of total extracellular Na+ to extracellular water; hypernatremia often indicates water loss (dehydration) rather than excess sodium, while hyponatremia often indicates water excess.
- Regulation: Kidneys (reabsorption/elimination) under hormonal control (e.g., aldosterone).
Potassium (K+)
- Role: Predominant intracellular cation; essential for membrane potential, nerve impulse conduction, and muscle contraction.
- ECF reference: about $3.5$–$5.0\ \mathrm{mmol/L}$ (clinical thresholds vary).
- Clinical significance: Hyperkalemia is commonly defined when K+ $>5\ \mathrm{mmol/L}$; levels $>6$–$7\ \mathrm{mmol/L}$ may be life-threatening depending on rate of rise. Causes include reduced renal excretion, transcellular shifts (acidosis, insulin deficiency, hemolysis), and excessive intake or intravenous administration.
Chloride (Cl^-)
- Role: Major extracellular anion; helps maintain electroneutrality, osmotic pressure and water distribution.
- Reference plasma range: $97$–$107\ \mathrm{mmol/L}$.
- Clinical notes: Hyperchloremia can occur with dehydration, renal tubular acidosis, or metabolic acidosis with bicarbonate l
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Electrolytes Overview
Klíčová slova: Essential elements, Periodic table, Electrolytes, Sodium disorders, Magnesium, Medical biochemistry
Klíčové pojmy: Electrolytes are ions that regulate fluid balance, nerve/muscle excitability, and pH, ECF osmolarity is mainly determined by sodium concentration, Major electrolytes include Na+, K+, Ca^{2+}, Cl^-, HCO_3^-, HPO_4^{2-}, Mg^{2+}, Normal plasma ranges: Na+ $136$–$145$ mmol/L, total Ca^{2+} $2.25$–$2.75$ mmol/L, HCO_3^- $22$–$26$ mmol/L, Hyperkalemia often defined as K+ $>5$ mmol/L; severity depends on absolute level and rate of rise, Bicarbonate buffer system is central to pH regulation and is controlled by lungs and kidneys, Common causes of imbalance: fluid loss, renal disease, medications, endocrine disorders, tumor lysis, Diagnosis relies on history, physical exam, blood/urine tests and ECG when indicated, Treatment: correct underlying cause, replace/remove electrolytes, monitor levels and cardiac status, Ionized fractions (e.g., ionized Ca^{2+}, ionized Mg^{2+}) better reflect biological activity