Comparison of Aldosterone and ADH (Antidiuretic Hormone)

Overview

• The lecture focuses on comparing the actions of Aldosterone and ADH in the nephron, highlighting their effects on water permeability, sodium, potassium management, volume, and osmolarity.

Nephron Functionality

• Nephron Structure:
  • Tubule with cells lining it, facilitating urine passage.
  • Adjacent blood vessel for substance exchange.
• Membrane Permeability:
  • Aldosterone Side: Water permeable membranes.
  • ADH Side: Non-water permeable membranes.

Aldosterone Function

• Primary Role: Pulls in sodium (Na⁺) and expels potassium (K⁺) into urine.
• Sodium Permeability: Sodium cannot easily cross membranes, contributing to increased tonicity.
• Potassium Permeability: Potassium can slightly cross membranes.
• Effect on Tonicity: Increases blood vessel tonicity, drawing water into blood vessels and increasing blood volume.

ADH (Antidiuretic Hormone) Function

• Water Channels: Facilitates water movement through water channels in otherwise impermeable membranes.
• Mechanism: Directly increases water volume without changing osmoles.

Effects on Volume and Osmolarity

• Aldosterone:
  • Increases both osmoles and volume.
  • Does not affect osmolarity since both numerator (osmoles) and denominator (volume) increase proportionally.
• ADH:
  • Primarily increases volume.
  • Does not change osmoles, thus decreases osmolarity (since volume increases and osmoles remain unchanged).

Hormone Application Scenarios

1. Increase Volume, Maintain Osmolarity:
   • Use aldosterone, as it increases volume without affecting osmolarity.
   • Avoid ADH.
2. Increase Volume, Regardless of Osmolarity:
   • Use both aldosterone and ADH.
   • Useful in emergencies (e.g., blood loss from an accident).
3. Decrease Osmolarity, Regardless of Volume:
   • Use ADH, which decreases osmolarity.
   • Aldosterone is not needed if volume changes are acceptable.
4. Decrease Osmolarity, Maintain Volume:
   • Use ADH to decrease osmolarity.
   • Adjust aldosterone downwards slightly to maintain volume.

Conclusion

• The combination and manipulation of aldosterone and ADH levels can effectively manage blood volume and osmolarity depending on physiological needs.
• Understanding these hormone interactions enables better prediction and management of body fluid dynamics in different scenarios.