Angiotensin II induced thirst is
**Core Concept**
Angiotensin II is a potent vasoconstrictor and a key component of the renin-angiotensin-aldosterone system (RAAS), which regulates blood pressure and fluid balance. The sensation of thirst is mediated by the hypothalamus, specifically the subfornical organ and the organum vasculosum of the lamina terminalis, which respond to circulating angiotensin II.
**Why the Correct Answer is Right**
Angiotensin II stimulates the release of vasopressin (ADH) and also directly acts on the hypothalamus to increase the sensation of thirst. This is achieved through the activation of angiotensin II type 1 (AT1) receptors in the hypothalamus, which triggers a signal transduction cascade leading to the expression of genes involved in water reabsorption and vasopressin release. The resulting increase in vasopressin levels promotes water reabsorption in the collecting ducts of the kidneys, increasing blood volume and reducing blood pressure.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect as there is no established link between angiotensin II and the sensation of hunger.
* **Option B:** This option is incorrect as vasopressin (ADH) primarily regulates water reabsorption in the kidneys, rather than inducing thirst.
* **Option C:** This option is incorrect as the primary action of angiotensin II is vasoconstriction, rather than inducing a sensation of thirst.
**Clinical Pearl / High-Yield Fact**
The subfornical organ and organum vasculosum of the lamina terminalis are unique in that they lack a blood-brain barrier, allowing circulating angiotensin II to directly access and stimulate the hypothalamus, thereby regulating thirst and vasopressin release.
**Correct Answer: C. Angiotensin II directly stimulates the hypothalamus to increase the sensation of thirst.**