Why does an elderly patient with impaired kidney function and reduced ADH secretion still experience a strong sense of thirst despite being mildly dehydrated?

💡 Explanation

The thirst mechanism is triggered by rising plasma osmolality. In elderly patients with kidney dysfunction, the osmolality set-point for triggering thirst can increase because of reduced renal concentrating ability and ADH response; therefore, even mild dehydration results in a strong thirst response at a higher osmolality, rather than other triggers dominating at lower osmolality levels.

• Why does rubbing the skin around an injury reduce pain, according to the gate control theory of pain?
• If a patient's cardiac preload suddenly decreases during rapid blood loss, which consequence follows related to cardiovascular hemodynamics?
• Why does the perceived intensity of a light source diminish more slowly than predicted by the inverse square law when viewed peripherally?
• A chronic Pseudomonas aeruginosa lung infection is treated with tobramycin. Which resistance mechanism most directly allows the bacteria to persist despite initially effective antibiotic concentrations?
• During prolonged starvation, why does the liver increase gluconeogenesis despite elevated circulating cortisol levels, which would seem to suppress glucose demand?
• Why does the cardiac output of an endurance athlete often remain relatively stable at rest despite having a significantly lower resting heart rate compared to a sedentary individual?