Study Notes on Body Fluids, Electrolytes, and Hyponatremia

Overview of Body Fluids and Electrolytes

  • Body fluids consist of a combination of:
      - Water
      - Acids
      - Bases
      - Dissolved substances, known as solutes

Electrolytes

  • Definition: Electrically charged particles present in body fluids.
  • Most abundant electrolyte: Sodium
  • Function of electrolytes:
      - Sustain normal cellular functions
      - Maintain appropriate blood volume

Homeostasis

  • Definition: The process of maintaining stable internal conditions despite external changes.
  • Importance: Ensures the concentrations of sodium and other solutes remain within a narrow range to support cellular functions and overall health.

Serum Sodium

  • Definition: The concentration of sodium in blood plasma.
  • Normal serum sodium range: 135 to 145 milliequivalents per liter (mEq/L).

Hyponatremia

  • Definition: A medical condition characterized by a serum sodium level lower than 135 mEq/L.
  • Types of hyponatremia:
      - Dilutional Hyponatremia:
        - Most common type
        - Caused by an excess of extracellular water relative to sodium concentration.
        - Description of mechanism:
          - Increased water intake, potentially excessive.
          - This excess water dilutes sodium levels in the blood, causing hyponatremia.

Causes of Low Serum Sodium

  • Chronic Kidney Disease:
      - Pathophysiology:
        - Kidneys fail to filter adequate amounts of fluids and waste products from blood.
        - Resulting effect: Dilution of blood sodium levels and water retention in interstitial spaces.
      - Consequence:
        - Extracellular water moves into cells, causing them to swell, which can lead to cellular damage and functional impairment.

Treatments for Hyponatremia

  • Water Restriction:
      - Mechanism: Reduces excess water, allowing movement via osmosis from the cell back into extracellular fluid.
  • Hypertonic Saline Solution:
      - Definition: A solution with a sodium concentration higher than that of normal extracellular fluid.
      - Purpose: To restore blood sodium levels to their normal range.
  • Antidiuretic Hormone (ADH) Inhibitors:
      - Function:
        - Help kidneys retain electrolytes.
        - Increase water excretion in urine to correct sodium balance.