Cortisol and the Adrenal Axis

Introduction

• Cortisol is a glucocorticoid steroid hormone secreted by the adrenal glands.
• The adrenal glands are located above the kidneys in the abdomen.
• Cortisol acts as a stress hormone, aiding the body in handling stress.
• Functions include:
  • Increasing alertness
  • Inhibiting the immune system
  • Reducing inflammation
  • Inhibiting bone formation
  • Raising blood glucose levels
  • Increasing metabolism
  • Supporting cardiovascular function (heart rate, blood pressure, cardiac output)

Cortisol Release

• Released in pulses throughout the day and in response to stress.
• Exhibits diurnal variation:
  • Peaks in the early morning
  • Lowest in the evening
• Additional spikes can occur due to stress.

Types of Steroid Hormones

• Glucocorticoids: e.g., cortisol, regulate immune response and reduce inflammation (e.g., prednisone, hydrocortisone, dexamethasone).
• Mineralocorticoids: e.g., aldosterone, regulate electrolytes and blood pressure (e.g., fludrocortisone).
  • Act on kidney nephrons to manage sodium, potassium, and hydrogen secretion.
  • Affect blood pressure by altering fluid volume in blood vessels.

Hypothalamic-Pituitary-Adrenal Axis (HPA Axis)

• Involves the hypothalamus and anterior pituitary.
• Hypothalamus releases CRH (corticotropin-releasing hormone).
• CRH stimulates ACTH (adrenocorticotropic hormone) release from the pituitary.
• ACTH stimulates cortisol release from adrenal glands.
• Negative Feedback: Cortisol suppresses CRH and ACTH release.

Effects of Exogenous Steroids

• Long-term use of glucocorticoids can suppress natural cortisol production.
• Sudden cessation can lead to adrenal crisis.
• Gradual reduction is necessary to resume normal glucocorticoid production.

Cushing's Syndrome

• Caused by excessive glucocorticoids/cortisol.
• Causes include:
  • Cushing's Disease: Pituitary adenoma secretes excessive ACTH.
  • Adrenal adenoma secreting cortisol.
  • Paraneoplastic syndrome (e.g., ectopic ACTH from lung cancer).
  • Exogenous steroid use.
• Symptoms: moon face, central obesity, muscle wasting, hypertension, diabetes, osteoporosis.

Adrenal Insufficiency

• Insufficient cortisol production.
• Symptoms include fatigue, muscle weakness, low blood pressure, and hyperpigmentation.
• Types:
  • Primary (Addison's Disease): Damaged adrenal glands (often autoimmune).
  • Secondary: Inadequate ACTH from pituitary.
  • Tertiary: Inadequate CRH from hypothalamus (often due to exogenous glucocorticoid use).
• Adrenal Crisis: Emergency condition requiring immediate hydrocortisone.

Testing

• Cortisol and ACTH Levels: Fluctuate throughout the day, early morning testing recommended.
• Dynamic Tests:
  • Short Synacthen Test: Diagnoses adrenal insufficiency by measuring cortisol response to synthetic ACTH.
  • Dexamethasone Suppression Test: Used for Cushing's syndrome, assesses cortisol suppression after dexamethasone.

Additional Information

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