Final answer:
Osmoreceptors in the hypothalamus detect increased solute concentrations due to water loss and signal the release of antidiuretic hormone (ADH) from the posterior pituitary gland to increase water reabsorption in the kidneys.
Step-by-step explanation:
The specialized cells in the hypothalamus that detect increased solute concentration in extracellular fluid due to water loss are known as osmoreceptors. These osmoreceptors are sensitive to changes in the blood's osmolality, particularly to the concentration of sodium ions and other solutes.
When the solute concentration rises, due to factors such as dehydration, the osmoreceptors signal the posterior pituitary gland to release antidiuretic hormone (ADH), also known as vasopressin. ADH targets the kidneys, increasing water reabsorption, thereby diluting the blood plasma and lowering solute concentration. The release of ADH is governed by a negative feedback loop to maintain homeostasis.