Lecture Notes: Human Anatomy and Physiology - Urinary System and Fluid, Electrolyte, and Acid-Base Balance

Episode 3: Regulation of Water and Electrolyte Levels

Key Concepts

• Human Body Composition:
  • Primarily consists of water.
  • Two main compartments: Intracellular Fluid (ICF) and Extracellular Fluid (ECF).

Regulation Mechanisms

• Water and Electrolyte Regulation:
  • Controlled by mechanisms regulating solute and water movement between ECF and ICF.
  • Plasma membrane separates ICF and ECF, regulating fluid composition.
  • Pores, ion channels, and active transport allow ions (e.g., sodium, potassium) to move across membranes.
  • Unequal electrolyte concentration across membranes creates electrical charge differences.

Fluid Balance and Electrolyte Balance

• Imbalances:
  • Changes in sodium ion concentration in ICF affect osmotic pressure in the interstitial fluid.
  • Water moves from interstitial fluid to ICF via osmosis if interstitial fluid becomes hypotonic.

Sodium-Potassium Pump

• Mechanism:
  • Requires ATP; breaks down into ADP and inorganic phosphate.
  • Transfers sodium out of the cytoplasm into ECF and potassium into the cytoplasm.
  • Maintains high potassium and low sodium levels in ICF.
  • Form of active transport using ATP energy.

Types of Pressure

• Four Types of Pressure Modulating Fluid and Electrolyte Levels:
  • Interstitial Fluid Hydrostatic Pressure: Generated by water in the interstitial fluid.
  • Blood Hydrostatic Pressure: Generated by water in capillaries; highest at arterial end.
  • Blood Colloid Osmotic Pressure: Generated by plasma proteins; retains water like a sponge.
  • Interstitial Fluid Colloid Osmotic Pressure: Generally close to zero due to lack of proteins.
• Pressure Sum and Fluid Transfer:
  • No fluid transfer if the sum of pressures inside and outside compartments are equal.
  • Fluid shifts based on the sum of pressures exceeding or being lower than opposing pressures.

Capillary Exchange

• Arterial End of Capillaries:
  • High blood hydrostatic pressure moves fluid out of capillaries into interstitial fluid.
• Venous End of Capillaries:
  • Lower blood hydrostatic pressure and higher osmotic pressure move fluid into capillaries.

Clinical Example: Edema

• Causes of Edema:
  • Allergy, decrease in blood osmotic pressure (e.g., decreased plasma proteins).
  • Increased capillary blood pressure (e.g., heart failure).
  • Electrolyte retention, especially sodium, due to increased aldosterone or kidney disease.

Summary

• Fluid and electrolyte imbalances cause significant physiological changes.
• Active transport and pressure dynamics play crucial roles in maintaining balance.
• Clinical conditions like edema illustrate the consequences of imbalance.