The adrenal glands are endocrine glands consisting of a cortex and medulla, and they regulate the stress response, electrolytes, and glucose metabolism. Let us organize the types and actions of adrenal cortex hormones (steroids).
Basic Knowledge
Structure of the adrenal gland:
・Adrenal cortex: Three layers—the zona glomerulosa, zona fasciculata, and zona reticularis. It synthesizes steroid hormones from cholesterol.
・Adrenal medulla: Chromaffin cells. Under sympathetic control, it secretes catecholamines (adrenaline and noradrenaline).
Three groups of adrenal cortex hormones:
① Glucocorticoids (cortisol and corticosterone): Secreted by the zona fasciculata.
・Promote gluconeogenesis (proteins and lipids → glucose) → increased blood glucose
・Powerful anti-inflammatory and immunosuppressive effects
・The central hormones of the stress response.
・Regulation of secretion: hypothalamus (CRH) → anterior pituitary (ACTH) → adrenal cortex (cortisol), with negative feedback.
② Mineralocorticoids (aldosterone): Secreted by the zona glomerulosa.
・Increase Na reabsorption and K excretion in the kidney's collecting ducts → increased blood pressure and fluid volume.
・Regulated by the renin-angiotensin-aldosterone system (RAAS).
③ Adrenal androgens (DHEA): Secreted by the zona reticularis. Precursors of sex hormones.
Stress response (HPA axis): Stress stimulus → increased hypothalamic CRH → increased pituitary ACTH → increased adrenal-cortex cortisol → emergency response through increased blood glucose, anti-inflammatory action, and immunosuppression. During chronic stress, persistently high cortisol levels cause decreased immunity, osteoporosis, hyperglycemia, and other effects.
Answer: The significance of cortisol secretion during acute stress is that cortisol promotes gluconeogenesis and raises blood glucose, ensuring an emergency energy supply for the muscles and brain. Its anti-inflammatory action also suppresses excessive inflammatory responses to tissue damage and prepares the body to respond immediately to stress. The mechanism of decreased immunity during chronic stress is that persistently high cortisol levels suppress the proliferation and activation of T cells, B cells, and NK cells and reduce the production of cytokines such as interleukins. The thymus also atrophies, reducing lymphocyte production itself; therefore, resistance to infectious diseases and cancer decreases.
- Adrenal cortex = produces steroid hormones using cholesterol as the raw material
- Glucocorticoids (cortisol) = increased gluconeogenesis, anti-inflammatory action, immunosuppression
- Mineralocorticoids (aldosterone) = increased renal Na reabsorption and increased blood pressure
- HPA axis = hypothalamus (CRH) → pituitary (ACTH) → adrenal cortex (cortisol)
- Adrenal medulla = secretes adrenaline (peptide-like catecholamine)
- Chronic stress = chronically high cortisol → immunosuppression and osteoporosis
Practice
- Explain how aldosterone acts on the kidneys to raise blood pressure.
- State why synthetic glucocorticoids (prednisolone) are used as anti-inflammatory drugs.
- Give an example of a disease that may occur if negative feedback in the HPA axis fails.