M04.03.06 Aldosterone

Aldosterone is a steroid hormone produced by the adrenal cortex, part of the renin-angiotensin-aldosterone system (RAAS). It plays a critical role in maintaining electrolyte balance and blood pressure by acting on the kidneys.

Key Functions of Aldosterone

1. Sodium Reabsorption:
   • Aldosterone increases sodium (Na+) reabsorption in the principal cells of the kidney’s distal convoluted tubules and collecting ducts.
   • This reabsorption helps to regulate extracellular fluid volume and blood pressure.
2. Potassium Secretion:
   • Aldosterone also promotes potassium (K+) secretion into the urine by the same principal cells.
   • By managing potassium levels, aldosterone ensures proper muscle function and nerve signaling.

Regulation of Aldosterone Release

Aldosterone secretion is primarily controlled by two factors:

1. Plasma Angiotensin II (Ang II):
   • Angiotensin II is produced in response to low blood pressure or low sodium levels, stimulating aldosterone release.
2. Plasma Potassium (K+):
   • Elevated plasma potassium levels directly stimulate aldosterone release to enhance potassium excretion.

Factors Stimulating Aldosterone Release

Points to Remember

• Aldosterone is essential for regulating blood pressure and electrolyte balance.
• Sodium reabsorption by aldosterone helps increase extracellular volume, while potassium secretion maintains potassium homeostasis.
• Two key stimuli for aldosterone release are plasma angiotensin II and elevated plasma potassium.

Bibliography

• Hall, J. E., & Guyton, A. C. (2015). Guyton and Hall Textbook of Medical Physiology (13th ed.). Saunders.
• Marieb, E. N., & Hoehn, K. (2018). Human Anatomy & Physiology (11th ed.). Pearson.
• Young, D. B. (2010). Regulation of Fluid and Electrolyte Balance.