The 4 arrows - aldosterone action-NW2017
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The renal actions of the most potent mineralocorticoid hormone Aldosterone are conceptualized as the 4 arrows in action, in the context of the regulation of the blood volume and pressure and the plasma electrolytes, sodium and potassium.
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The 4 arrows - aldosterone action-NW2017
- 1. Aldosterone Action The FOUR arrows Nyunt Wai 2017 victor.nwai@gmail.com
- 3. Kidney: Juxtaglomerular (JG) cells Kidney: Juxtaglomerular (JG) cells Fall in renal perfusion pressure Renin Renin Fall in blood volume and/or pressure
- 4. Renin Renin Increased sympathetic discharge Baroreceptor reflex Increased sympathetic discharge Fall in blood volume and/or pressure Kidney: Juxtaglomerular (JG) cells Kidney: Juxtaglomerular (JG) cells
- 5. Renin Renin Angiotensinogen Angiotensin I Angiotensin II Angiotensin Coverting Enzyme
- 8. Aldoster one
- 9. Aldostero neC o l l e c t i n g d u c t c e l l s
- 10. 4 arrows T u b u l a r f l u i d I n t e r s t i t i a l f l u i d B l o o d Aldoster one Action H2O Na+ K+ H+ or
- 11. 4 arrows T u b u l a r f l u i d I n t e r s t i t i a l f l u i d B l o o d Aldoster one Action H2O Na+ K+ H+ or H2O Na+ K+ Blood volume blood pressure Regulation of plasma potassium levels
- 12. 4 arrows T u b u l a r f l u i d I n t e r s t i t i a l f l u i d B l o o d Aldoster one Action H2O Na+ K+ H+ or H2O Na+ K+ Blood volume blood pressure Regulation of plasma potassium levels Conn’s syndrome (Primary hyperaldosteronism) Hypervolemia Hypertension Hypokalemia Metabolic alkalosis [H+]
- 13. Conn’s syndrome (Primary hyperaldosteronism) Hypervolemia Hypertension Metabolic alkalosis Hypokalemia
- 14. Hypovolemia Hypotension Hyperkalemia Metabolic acidosis Addison’s Disease (Primary hypo-aldosteronism)
- 15. Hypovolemia Hypotension Hyperkalemia Metabolic acidosis Addison’s Disease (Primary hypo-aldosteronism)
Editor's Notes
- Being a steroid hormone, Aldosterone enters the collecting duct cells and acts on gene expression which activates sodium transport proteins. At the luminal border of the cells bathing the tubular fluid, the 4 arrows represent aldosterone actions. First, sodium ions enter the cell through epithelial sodium channels, setting up an osmotic gradient which draws water into the cell. Remember, water follows wherever sodium goes. And for each sodium ion entering the cell, either one potassium ion or one hydrogen ion moves out into the tubular fluid, and got excreted in the urine..
- Now, what are the effects of the 4 arrows or 4 actions of Aldosterone? First, sodium ions that have entered the cell activate the sodium potassium pump in the basolateral border. The pump transports sodium out of the cell into the interstitial fluid. Sodium ions then diffuse into the blood of the peritubular capillaries. Again, water follows sodium. Sodium and water in the blood plasma maintains the blood volume and blood pressure. Remember, sodium forms the backbone of the extracellular fluid volume, including the blood volume. And the blood volume is one of the determinants of blood pressure. Higher than normal plasma levels of potassium directly stimulates the adrenal cortex to secrete Aldosterone. Remember? Aldosterone action results in secretion of potassium ions into the tubular fluid in exchange for sodium, until the plasma potassium levels fall back to normal.
- Understandably, the 4 actions of aldosterone and their respective effects will be exaggerated when aldosterone levels are constantly higher than normal such as in the case of tumours of the adrenal cortex, for example, Conn’s syndrome. Sodium retention in the blood results in increased blood volume and higher than normal blood pressure called hypertension. Increase loss of potassium into the tubular fluid and its subsequent loss in the urine results in low plasma potassium levels or hypokalaemia. Increased hydrogen ion secretion into the tubular fluid causes lower than normal plasma hydrogen ion concentration or metabolic alkalosis.
- Such effects occur when aldosterone actions or the 4 arrows are massive and prolonged.
- When the Aldosterone secretion is lower than normal, as in Addison’s disease where hormone-secreting cells of the adrenal cortex are destroyed by some disease process, the 4 actions or the 4 arrows of aldosterone became attenuated, resulting in the effects opposite to that seen in hyperaldosteronism. So remember the 4 arrows when it comes to the role of this important mineralocorticoid in the regulation of blood volume and plasma electrolytes, sodium and potassium. That’s all for now.
- When the Aldosterone secretion is lower than normal, as in Addison’s disease where hormone-secreting cells of the adrenal cortex are destroyed by some disease process, the 4 actions or the 4 arrows of aldosterone became attenuated, resulting in the effects opposite to that seen in hyperaldosteronism. So remember the 4 arrows when it comes to the role of this important mineralocorticoid in the regulation of blood volume and plasma electrolytes, sodium and potassium. That’s all for now.