**Core Concept**
Conn's syndrome is a condition characterized by primary aldosteronism, a disorder of the adrenal gland that leads to excessive production of aldosterone, a mineralocorticoid hormone. This hormonal imbalance causes an increase in sodium reabsorption and potassium excretion in the kidneys, resulting in hypertension and hypokalemia.

**Why the Correct Answer is Right**
In Conn's syndrome, the excessive production of aldosterone is due to an aldosterone-producing adenoma (APA) in the adrenal cortex. The adenoma stimulates the zona glomerulosa to produce more aldosterone, leading to an increase in sodium reabsorption and potassium excretion. This results in hypertension, hypokalemia, and often, metabolic alkalosis.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the underlying cause of Conn's syndrome, which is an aldosterone-producing adenoma.
**Option B:** This option is incorrect because it mentions cortisol, which is a glucocorticoid hormone and not directly related to the pathophysiology of Conn's syndrome.
**Option C:** This option is incorrect because it mentions pheochromocytoma, a condition characterized by excessive production of catecholamines, which is not related to Conn's syndrome.

**Clinical Pearl / High-Yield Fact**
In Conn's syndrome, the presence of hypokalemia and hypertension should raise suspicion of primary aldosteronism. A diagnosis can be confirmed with a plasma aldosterone-to-renin ratio (ARR) or a saline infusion test.

**Correct Answer:** C.