Adrenal gland hormones-Chemistry, Secretion, Functions and Regulations of Adrenal Cortex hormones (glucocorticoids and mineralocorticoids)

1. Adrenal Cortex – Overview

The adrenal gland has two main parts:

  • Adrenal cortex → produces steroid hormones (glucocorticoids, mineralocorticoids, and androgens).

  • Adrenal medulla → produces catecholamines (epinephrine and norepinephrine).

We’ll focus on cortical hormones:

  • Glucocorticoids (mainly cortisol in humans)

  • Mineralocorticoids (mainly aldosterone)

2. Chemistry

  • Both glucocorticoids and mineralocorticoids are steroid hormones.

  • Derived from cholesterol through a series of enzymatic reactions.

  • Lipid-soluble, so they can easily cross cell membranes and bind to intracellular receptors.

3. Secretion

  • Glucocorticoids (cortisol) → secreted mainly by the zona fasciculata of the adrenal cortex.

  • Mineralocorticoids (aldosterone) → secreted mainly by the zona glomerulosa of the adrenal cortex.

Secretion pattern:

  • Cortisol → shows diurnal rhythm (high in early morning, low at midnight).

  • Aldosterone → secretion depends on renin-angiotensin system and blood electrolyte levels.

4. Functions

A. Glucocorticoids (Cortisol)

  • Metabolic functions:

    • ↑ Gluconeogenesis (raises blood glucose).

    • ↑ Protein breakdown (especially in muscles).

    • ↑ Lipolysis (fat breakdown).

  • Anti-inflammatory & immunosuppressive:

    • Inhibits release of inflammatory mediators (prostaglandins, histamine).

    • Decreases immune cell activity.

  • Stress response: Helps body cope with physical and emotional stress.

  • Other effects: Maintains blood pressure, bone metabolism, and mood stability.

B. Mineralocorticoids (Aldosterone)

  • Main role: Regulates water and electrolyte balance.

  • ↑ Sodium (Na⁺) reabsorption in kidneys.

  • ↑ Potassium (K⁺) and hydrogen ion excretion.

  • Indirectly helps maintain blood volume and blood pressure.

5. Regulation

Glucocorticoids (Cortisol)

  • Controlled by Hypothalamic–Pituitary–Adrenal (HPA) axis:

    • Hypothalamus → releases CRH (Corticotropin-Releasing Hormone).

    • Anterior pituitary → releases ACTH (Adrenocorticotropic Hormone).

    • Adrenal cortex (zona fasciculata) → secretes cortisol.

  • Negative feedback: High cortisol inhibits CRH and ACTH secretion.

Mineralocorticoids (Aldosterone)

  • Mainly regulated by the Renin–Angiotensin–Aldosterone System (RAAS):

    • Low blood pressure or low Na⁺ → kidney releases renin.

    • Renin → converts angiotensinogen → angiotensin I.

    • Angiotensin I → converted to angiotensin II (by ACE).

    • Angiotensin II → stimulates zona glomerulosa → aldosterone secretion.

  • Also influenced by:

    • Plasma K⁺ levels (high K⁺ stimulates aldosterone).

    • ACTH (minor effect).

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