Addison's Disease: Diagnosis and Clinical Features

Adrenal Gland Structure and Function

• The adrenal gland has two main parts: the suprarenal cortex and the suprarenal medulla
• The suprarenal cortex secretes steroid hormones essential for life, while the suprarenal medulla secretes norepinephrine and epinephrine

Adrenal Gland Cell Types and Hormones

• The suprarenal cortex has three zones: zona glomerulosa, zona fasciculata, and zona reticularis
• The zona glomerulosa produces mineralocorticoids (mainly aldosterone), zona fasciculata produces glucocorticoids (mainly cortisol), and zona reticularis produces sex corticoids
• The suprarenal medulla produces catecholamines (epinephrine and norepinephrine)

Adrenal Cortex Hormones

• Mineralocorticoids:
  • Produced by zona glomerulosa
  • Stimulated by increased blood K+ level and angiotensin II
  • Principal action: increases blood level of Na+ and water, and increases blood level of K+
• Glucocorticoids:
  • Produced by zona fasciculata and zona reticularis
  • Stimulated by ACTH and circadian rhythm
  • Principal action: influences protein breakdown, stimulates gluconeogenesis, suppresses inflammation, and depresses immune response
• Androgens:
  • Produced by zona reticularis
  • Stimulated by ACTH
  • Principal action: contributes to growth of axillary and pubic hair, and contributes to libido and sources of estrogen after menopause

Adrenal Medulla Hormones

• Epinephrine and norepinephrine:
  • Produced by adrenal medulla
  • Stimulated by sympathetic preganglionic neurons
  • Principal action: enhances effects of sympathetic part of autonomic nervous system during stress

Hypothalamic-Pituitary-Adrenal Axis

• Corticotropin-Releasing Hormone (CRH):
  • 41 amino acids
  • Transmitted by the hypophyseal portal vessels to the Adenohypophysis
  • Stimulates ACTH release
• Adrenocorticotrophic Hormone (ACTH):
  • 39 amino acids, 4.5kDa
  • Found free in the plasma, life of a few minutes
  • Stimulates synthesis of cortisol and other corticosteroids

Addison's Disease

• Caused by autoimmune destruction of the adrenal cortex
• Aetiology: autoimmunity, tuberculosis, secondary depositions (sarcoidosis, amyloidosis, hemochromatosis)
• Clinical features: gastrointestinal symptoms, hyperpigmentation, weight loss, general tiredness, hypotension, vitiligo, acute abdominal crises, muscle weakness, vomiting, diarrhea, and sweating

Cushing's Syndrome

• Caused by hypersecretion of cortisol
• Discovered in 1932
• Symptoms: obesity, round rose face, and others associated with prolonged exposure to high levels of cortisol
• Diagnosis: 24hr urine for cortisol, and other tests

Regulation of Aldosterone Secretion

• Regulated by the renin-angiotensin-aldosterone pathway
• Stimulated by increased blood K+ level and angiotensin II

Disorders of the Adrenal Cortex

• Hypocortisolaemia:
  • Primary: Addison's disease
  • Secondary: hypothalamic or pituitary
• Hypercortisolaemia:
  • Primary: Cushing's syndrome
  • Secondary: Cushing's disease

Negative Feedback Regulation of Glucocorticoid Secretion

• High level of CRH and low level of glucocorticoids promote release of ACTH, which stimulates glucocorticoid secretion by the suprarenal cortex

This quiz covers the causes, symptoms, and diagnosis of Addison's disease, a cortisol deficiency disorder. Topics include etiology, clinical features, and diagnostic procedures.