Endocrinology Lecture: Hypothalamic-Pituitary-Adrenal Axis

Overview

• Focus on the hypothalamic-pituitary axis and adrenal corticotropic hormones.
• Discusses adrenal gland hormones.

Brain Structures in Hormone Regulation

• Hypothalamus: Main regulator of body hormones.
• Pituitary Gland: Located below the hypothalamus.
  • Made up of anterior and posterior lobes.
  • Focus on the anterior pituitary regarding adrenal hormones.

Adrenal Glands

• Located above the kidneys; two adrenal glands.
• Structure:
  • Adrenal medulla (center).
  • Adrenal cortex (outer layer).

Adrenal Medulla

• Stimulated by sympathetic nerves.
• Secretes adrenaline and noradrenaline (epinephrine and norepinephrine).
• Triggers fight-or-flight response during acute stress.

Adrenal Cortex

• Responsible for long-term stress response.
• Composed of three layers: zona glomerulosa, zona fasciculata, zona reticularis (GFR mnemonic).

Hormones and Their Functions

1. Mineral Corticoids (e.g., Aldosterone)

• Secreted by zona glomerulosa.
• Involved in blood pressure regulation via kidneys.
  • Increases sodium and water reabsorption; potassium excretion.
  • Works at distal convoluted tubule and collecting duct.

2. Glucocorticoids (e.g., Cortisol)

• Secreted by zona fasciculata.
• Functions:
  • Negative feedback to brain, reducing ACTH.
  • Causes hyperglycemia and insulin resistance.
  • Increases blood pressure and suppresses immune system.
  • Stimulates bone osteoclastic activity (risk of osteoporosis).

3. Androgens

• Secreted by zona reticularis.
• Minimal role in stress.
• Functions:
  • Promotes prostate growth and masculine characteristics in men.
  • Affects libido in females.

Additional Factors Influencing Hormone Release

Renin-Angiotensin-Aldosterone System (RAAS)

• Involves angiotensin II in aldosterone release.
• Low blood pressure stimulates renin release from juxtaglomerular cells.
• Renin initiates RAAS cascade leading to angiotensin II production.
  • Angiotensin II stimulates aldosterone to retain sodium and water, increasing blood pressure.

Conclusion

• Detailed exploration of adrenal cortex hormone functions and regulation.
• Importance of understanding hormone impact on stress and body functions.