- The adrenal gland is composed of distinct regions, each responsible for producing different hormones.
- The adrenal cortex is the outer layer of the adrenal gland and is primarily responsible for the synthesis of steroid hormones.
- Among these hormones, cortisol is a key glucocorticoid produced by the adrenal cortex.

- Cortisol plays a vital role in regulating metabolism, reducing inflammation, and helping the body respond to stress.
- In contrast, the adrenal medulla (the inner part of the adrenal gland) produces catecholamines such as adrenaline and noradrenaline, which are involved in the body's "fight or flight" response.

- The adrenal capsule is a thin connective tissue layer covering the adrenal gland, and the renal cortex is the outer portion of the kidney and is unrelated to cortisol synthesis.

Thus, the correct answer is the adrenal cortex because it contains the necessary enzymes and biochemical pathways to synthesize cortisol.

Key points:
- Adrenal cortex: Site of cortisol synthesis
- Cortisol: A glucocorticoid important for metabolism and stress response
- Adrenal medulla: Produces catecholamines, not cortisol
- Adrenal capsule and renal cortex: Not involved in cortisol production

Reference: Robbins Basic Pathology, 10th Edition, Chapter 15: The Adrenal Gland / Pages 635-638