Plasmaosmolaritet

Plasma osmolarity is a measure of the concentration of dissolved particles in the blood plasma. It is primarily determined by the concentrations of sodium, chloride, bicarbonate, and glucose. Normal plasma osmolarity in adults is typically between 275 and 295 milliosmoles per liter (mOsm/L). This value is crucial for maintaining the osmotic balance between the intracellular and extracellular fluid compartments, ensuring proper cell function and fluid distribution throughout the body.

The body tightly regulates plasma osmolarity through hormonal mechanisms, mainly involving the antidiuretic hormone (ADH) and the thirst sensation. When plasma osmolarity rises, indicating dehydration or high solute concentration, the hypothalamus detects this change and stimulates the release of ADH from the posterior pituitary gland. ADH then acts on the kidneys to increase water reabsorption, thereby reducing water loss and diluting the plasma. Simultaneously, an increased osmolarity triggers the sensation of thirst, encouraging fluid intake. Conversely, when plasma osmolarity decreases, ADH release is suppressed, leading to increased water excretion by the kidneys and a decrease in thirst.

Deviations from the normal range can indicate various physiological or pathological conditions. Elevated plasma osmolarity, or hyperosmolarity, can be caused by dehydration, uncontrolled diabetes mellitus (due to hyperglycemia), excessive salt intake, or certain medical conditions. Low plasma osmolarity, or hypo-osmolarity, can result from excessive water intake (dilutional hyponatremia), heart failure, or certain kidney diseases. Monitoring plasma osmolarity is therefore an important diagnostic tool in clinical practice for assessing hydration status, electrolyte balance, and the presence of underlying medical disorders.