Final answer:
The hypothalamus responds to higher blood osmolality by signaling the release of antidiuretic hormone (ADH) from the posterior pituitary gland, increasing water reabsorption in the kidneys and balancing blood osmolarity through a negative feedback loop.
Step-by-step explanation:
Upon detection of higher blood osmolality, the hypothalamus triggers a response to maintain homeostasis. Osmoreceptors within the hypothalamus monitor the concentration of solutes in the blood. When the blood becomes too concentrated, these receptors signal the posterior pituitary gland to release antidiuretic hormone (ADH), also known as vasopressin.
The release of ADH results in the kidneys reabsorbing more water, which decreases the urine output, increases urine concentration, and dilutes the blood plasma. This system operates on a negative feedback loop, regulating water balance to ensure that blood osmolarity is kept within its optimal range. When osmolality decreases, the secretion of ADH in turn diminishes, allowing more water to be excreted in the urine to avoid over-hydration.