Library · Physiology
Where thirst comes from
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Thirst does not just show up on its own. It is triggered by specialized neurons, the osmoreceptors, whose job is to monitor how concentrated the blood is. Think of a soup that gets more concentrated as it loses water, and someone tasting how concentrated it is.
The ones doing that job sit in the anterior hypothalamus, in the lower part of the brain, and what they sense is osmolality, that is, the amount of dissolved particles in the plasma, along with the plasma's volume and pressure.
When that concentration rises above the normal range, those neurons send the signal up to the cerebral cortex, the layer where things become conscious, and that is where the alert is felt as thirst.
The order matters here: conscious thirst, the urge to drink, appears at a somewhat higher threshold than vasopressin release.
In brief
Thirst starts with specialized neurons, the osmoreceptors, which monitor how concentrated the blood is.
A soup that gets more concentrated as it loses water, and someone tasting how concentrated it is.
Osmoreceptors in the anterior hypothalamus sense plasma osmolality, volume, and pressure.
When osmolality rises above the normal range, they send a signal to the cortex, which registers it as thirst.
Conscious thirst has a somewhat higher threshold than vasopressin release.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingPhysiology, Osmoreceptors, StatPearlsPublished
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