Overview
This lecture reviews the adrenal gland’s anatomy, the synthesis and functions of adrenocortical hormones (mineralocorticoids, glucocorticoids, and androgens), their regulation, and related disorders.
Adrenal Gland Structure
- The adrenal glands sit atop each kidney and have two main parts: cortex (outer) and medulla (inner).
- The cortex has three layers: zona glomerulosa (produces aldosterone), zona fasciculata (cortisol), and zona reticularis (androgens).
- All adrenocortical hormones are steroid hormones synthesized from cholesterol.
Hormone Synthesis & Regulation
- Cholesterol is converted to pregnenolone, the rate-limiting step in steroid synthesis.
- Zona glomerulosa is regulated mainly by angiotensin II and potassium for aldosterone production.
- Zona fasciculata is regulated by ACTH (adrenocorticotropic hormone) for cortisol synthesis.
- Each cortical layer operates with independent regulation.
Mineralocorticoids (Aldosterone)
- Aldosterone increases sodium and water reabsorption and promotes potassium and hydrogen ion excretion.
- Main regulators: angiotensin II and high blood potassium levels.
- Lack of aldosterone leads to sodium loss, hypovolemia, hyperkalemia, and potential circulatory shock.
- Excess aldosterone causes hypertension, hypokalemia, weakness, and metabolic alkalosis.
- Mechanism involves genomic effects via the mineralocorticoid receptor and possible non-genomic pathways.
Glucocorticoids (Cortisol)
- Cortisol mobilizes glucose, amino acids, and fats for energy during stress.
- Increases blood glucose via gluconeogenesis and insulin resistance.
- Promotes protein catabolism (except in the liver) and mobilizes fatty acids.
- Anti-inflammatory effects: stabilizes lysosomal membranes, decreases capillary permeability, suppresses WBC migration and T lymphocytes, reduces fever.
- Excess cortisol causes muscle wasting, fat redistribution, insulin resistance, and immunosuppression.
Regulation of Glucocorticoids
- Controlled via the hypothalamic-pituitary-adrenal axis: hypothalamus releases CRF, pituitary releases ACTH, adrenal cortex releases cortisol.
- Cortisol has negative feedback on ACTH and CRF.
Adrenal Disorders
- Addison’s disease (hypoadrenalism): deficiency in both mineralocorticoids and glucocorticoids; leads to shock and hypoglycemia.
- Cushing’s syndrome (hyperadrenalism): excess cortisol causes muscle weakness, fat redistribution, hyperglycemia, infections.
- Conn’s disease (hyperaldosteronism): excess aldosterone, hypertension, hypokalemia.
Key Terms & Definitions
- Adrenal cortex — outer part of adrenal gland producing corticosteroids.
- Aldosterone — main mineralocorticoid, regulates sodium and potassium balance.
- Cortisol — main glucocorticoid, regulates stress response and metabolism.
- ACTH — adrenocorticotropic hormone, stimulates cortisol secretion.
- Addison’s disease — adrenal insufficiency of mineralocorticoids and glucocorticoids.
- Cushing’s syndrome — excess cortisol state.
- Conn’s disease — primary hyperaldosteronism.
Action Items / Next Steps
- List the layers of the adrenal cortex and the hormones each produces.
- State two main consequences of low aldosterone.
- List four functions of cortisol.