## **Core Concept**
The major adrenocortical hormones are produced by the adrenal cortex and play critical roles in various bodily functions, including stress response, electrolyte balance, and metabolism. The three main types of adrenocortical hormones are glucocorticoids, mineralocorticoids, and androgens. Among these, cortisol is the most abundant and significant glucocorticoid.

## **Why the Correct Answer is Right**
Cortisol (**Option D**) is the major adrenocortical hormone in blood, produced primarily by the zona fasciculata of the adrenal cortex. It plays a vital role in response to stress and low blood glucose. Cortisol influences metabolism, immune response, and has anti-inflammatory properties. Its levels follow a circadian rhythm, peaking in the early morning and decreasing at night.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Aldosterone is a crucial mineralocorticoid but not the major adrenocortical hormone in blood. It primarily regulates sodium and potassium balance.
- **Option B:** Androstenedione is an androgen produced by the adrenal cortex but is not the major hormone in terms of concentration or clinical impact compared to cortisol.
- **Option C:** Dehydroepiandrosterone sulfate (DHEAS) is another androgen produced by the adrenal cortex and, while significant, especially in certain pathological conditions, it is not the major adrenocortical hormone in blood.

## **Clinical Pearl / High-Yield Fact**
A key clinical point to remember is that Cushing's syndrome results from excess cortisol levels. This can be due to various causes, including exogenous steroid use, ACTH-producing pituitary adenomas, or adrenal tumors. The diagnosis involves demonstrating elevated cortisol levels and failure of normal feedback inhibition.

## **Correct Answer:** . Cortisol