Metabolic mechanisms of development and compensation of osmotic stress in the brain

Extracellular fluid of the brain, consisting of cerebrospinal fluid and interstitial fluid, is normally isotonic to blood plasma. Problems arise with a rapid change in osmolality of circulating blood or interstitial brain fluid. The permeability of the blood-brain barrier is lower than in the peripheral capillaries, but this permeability is still several times greater than the passive permeability for electrolytes or glucose. Because of this difference, it is believed that the brain is like an osmometer: it swells with reduced plasma osmolality and contracts (dehydrated) when the plasma becomes hypertonic. Osmotic stress has a direct effect on the functioning of the brain and triggers physiological compensatory mechanisms, in the absence of which due to the intensity or duration of stress, irreversible serious complications may develop. Knowledge and understanding of these processes are the basis for preventing their development and treatment.