Final answer:
The increase in thirst stimulus causes the hypothalamus to trigger the release of antidiuretic hormone (ADH) from the posterior pituitary, instructing the kidneys to reabsorb more water and conserve body fluids.
Step-by-step explanation:
The thirst stimulus leads to an increase in the amount of antidiuretic hormone (ADH) released from the posterior pituitary. ADH, also known as vasopressin, is essential for water conservation in the body. When the concentration of blood plasma increases, which is often due to dehydration or the consumption of salty foods, osmoreceptors in the hypothalamus trigger the release of ADH. This hormone then instructs the kidneys to reabsorb more water, effectively reducing urine output and helping to dilute the blood plasma back to normal levels.
ADH operates by increasing the permeability of the kidney tubules to water by promoting the insertion of aquaporins into the cell membranes, thereby facilitating water reabsorption into the bloodstream and thus, leading to a decrease in blood osmolarity. Alcohol consumption can reduce ADH release, which is why drinking alcohol can lead to increased urine production and subsequent dehydration.