2. Polydipsia
Polydipsia, or excessive thirst, is the second of the three classic signs of elevated levels of blood glucose. The balance of the metabolism of water in the body is the result of a delicate interplay constituted by the sensation of thirst, the production of metabolic water, the ingestion of exogenous water contained in food and drink, and the expulsion of the same through the skin, the respiratory system, the gastrointestinal tract, and urinary system. Thirst is the subjective sensation that leads to the intake of water. The physiological factors that determine the appearance of an increased sensation of thirst are linked to an increase in the osmolarity of extracellular fluid and this is determined by an excess of salts, a deficit of fluids, and a decrease in the circulating vascular volume. The conscious desire to drink appears when plasma osmolarity reaches 295 mOsm/kg, which is continuously achieved and surpassed when blood glucose is too high. Factors such as sodium consumption normally influence the appearance of thirst, and a basic component of its stimulation is dryness of the mucous membranes of the mouth and pharynx, which is also commonly experienced by patients with elevated blood sugar.
