USMLE Guide: Adrenal Cortex

Introduction

The adrenal cortex is the outer part of the adrenal glands, which are located on top of each kidney. It plays a vital role in the production of hormones that are essential for maintaining various bodily functions. This USMLE guide aims to provide a comprehensive overview of the adrenal cortex, including its anatomy, hormone production, and related clinical conditions.

Anatomy of the Adrenal Cortex

The adrenal cortex is divided into three distinct zones, each responsible for producing different hormones:

1. Zona Glomerulosa:

   • Located in the outermost layer of the adrenal cortex.
   • Produces mineralocorticoids, mainly aldosterone.
   • Aldosterone regulates electrolyte and fluid balance in the body.

2. Zona Fasciculata:

   • Found in the middle layer of the adrenal cortex.
   • Produces glucocorticoids, primarily cortisol.
   • Cortisol is involved in regulating metabolism, immune response, and stress response.

3. Zona Reticularis:

   • Situated in the innermost layer of the adrenal cortex.
   • Produces androgens, including dehydroepiandrosterone (DHEA) and androstenedione.
   • These androgens contribute to the development of secondary sexual characteristics.

Hormones Produced by the Adrenal Cortex

1. Aldosterone:

   • Regulates sodium and potassium balance.
   • Acts on the distal tubules and collecting ducts of the kidneys.
   • Stimulated by angiotensin II and increased plasma potassium levels.

2. Cortisol:

   • Involved in glucose metabolism, particularly during stress.
   • Regulates immune responses and inflammatory reactions.
   • Influences protein and fat metabolism.
   • Secretion is controlled by the hypothalamic-pituitary-adrenal (HPA) axis.

3. Androgens:

   • Primarily produced in the zona reticularis.
   • Converted to testosterone and estrogens in peripheral tissues.
   • Responsible for the development of secondary sexual characteristics.

Clinical Conditions Associated with the Adrenal Cortex

1. Hyperaldosteronism:

   • Excessive production of aldosterone.
   • Leads to hypertension, hypokalemia, and metabolic alkalosis.
   • Primary hyperaldosteronism is commonly caused by adrenal adenoma.

2. Cushing's Syndrome:

   • Excessive production of cortisol.
   • Manifests as central obesity, moon face, buffalo hump, and muscle wasting.
   • Can result from prolonged use of glucocorticoid medications or adrenal tumors.

3. Adrenal Insufficiency:

   • Insufficient production of adrenal hormones.
   • Primary adrenal insufficiency (Addison's disease) is often caused by autoimmune destruction of the adrenal cortex.
   • Symptoms include fatigue, weight loss, hypotension, and hyperpigmentation.

4. Congenital Adrenal Hyperplasia (CAH):

   • Genetic disorder affecting adrenal steroid biosynthesis.
   • Most commonly caused by 21-hydroxylase deficiency.
   • Leads to cortisol deficiency and excessive androgen production.
   • Presents with ambiguous genitalia in females and precocious puberty in males.

Conclusion

Understanding the adrenal cortex is crucial for medical professionals. This USMLE guide has provided an informative overview of the adrenal cortex's anatomy, hormone production, and associated clinical conditions. Remember to review and consolidate this knowledge to excel in your usmle exams and in future medical practice.