Thirst

Stimulus for water intake

• Hypertonicity
• Hypovolaemia
• Hypotension
• Angiotensin II
• Others
  * Social factors
  * Psychological factors
  * Dryness of the pharyngeal mucosal membrane

• Increased effective osmotic pressure of plasma
• Decreases in ECF volume
  * Via angiotensin II 
• Psychological factors
• Social factors
• Dryness of the pharyngeal mucous membrane

Osmolality

Increased osmotic pressure

--> Acts on osmoreceptors
* Located in anterior hypothalamus

ECF volume

Decreased ECF volume

--> Increase renin secretion

--> Increase angiotensin II production

Angiotensin acts on subfornical organ (SFO)
--> Increase thirst

Some evidence that angiotensin might also act on organum vasculosum of the lamina terminalis (OVLT)

Others

• Baroreceptor in heart and blood vessels are also involved.
• Lesions of the anterior communicating artery can obtund thirst because branches of this artery supplies the hypothalamic area concerned with thirst