Thyroid and Adrenal Glands

2. Adrenal Glands

The adrenal cortex is the outer region of the adrenal gland and is responsible for the production of steroid hormones, collectively known as corticosteroids.
All adrenal cortical hormones are steroid-based and derived from cholesterol, but each cortical zone expresses distinct enzymes that determine which specific hormone is produced.
Together, these hormones enable the body to maintain metabolic stability, electrolyte balance, and adaptive responses to stress.

Main Hormone: Aldosterone
Primary Function: Regulates sodium (Na⁺) and potassium (K⁺) balance and maintains blood pressure.
Synthesis Pathway:
Cholesterol → Pregnenolone → Progesterone → 11-Deoxycorticosterone → Corticosterone → Aldosterone
Regulation:
- Controlled mainly by the renin–angiotensin–aldosterone system (RAAS) and plasma K⁺ levels.
- ACTH (from the pituitary) has a minor stimulatory role

Main Hormone: Cortisol
Primary Function: Influences glucose metabolism, stress response, immune modulation, and protein catabolism.
Synthesis Pathway:
Cholesterol → Pregnenolone → 17-Hydroxypregnenolone → 17-Hydroxyprogesterone → 11-Deoxycortisol → Cortisol
Regulation:
- Controlled by the hypothalamic–pituitary–adrenal (HPA) axis.
- CRH from the hypothalamus stimulates ACTH release from the pituitary, which in turn stimulates cortisol synthesis and secretion.
- Cortisol exerts negative feedback on both the hypothalamus and pituitary.

Main Hormones: Dehydroepiandrosterone (DHEA) and Androstenedione
Primary Function: Serve as precursors for sex hormones (testosterone and estrogen) and contribute to secondary sexual characteristics.
Synthesis Pathway:
Cholesterol → Pregnenolone → 17-Hydroxypregnenolone → DHEA → Androstenedione
Regulation:
- Stimulated by ACTH, similar to cortisol.
- No strong negative feedback system, so androgen levels depend largely on ACTH activity.