Fluid Balance Lecture by Dr. Mike

Introduction

• Fluid balance is essential for maintaining homeostasis in the human body.
• The human body is composed of 59 elements, but 99% is made up of six elements: Oxygen, Carbon, Hydrogen, Nitrogen, Phosphorus, and Calcium.
• Oxygen and Hydrogen primarily form water, which constitutes about 60% of the human body.

Body Water Composition

• For a 70 kg male, approximately 42 kg of body weight is water.
• Water is distributed across different compartments:
  • Intracellular Fluid (ICF): 28 liters (two-thirds of body water)
  • Extracellular Fluid (ECF):
    • Interstitial Fluid: 11 liters
    • Plasma: 3 liters

Fluid Balance Maintenance

• Intake:

  • Through food and beverages: ~2100 mL/day
  • Through metabolism (carbon metabolism): ~200 mL/day
  • Total intake: ~2300 mL/day

• Loss:

  • Insensible losses through lungs: ~700 mL/day
  • Sweating: Varies (100 mL/day under normal conditions, 1-2 liters during exercise)
  • Feces: ~100 mL/day
  • Urine (kidneys): ~1400 mL/day
  • Total loss: ~2300 mL/day

Water Movement Between Compartments

• Movement influenced by:
  • Semi-permeable membranes: capillary membrane and phospholipid bilayer
  • Capillary membrane: Impermeable to cells and large proteins
  • Phospholipid bilayer: Impermeable to large or charged particles

Role of Ions in Fluid Movement

• Ions like Sodium, Potassium, Magnesium, and Calcium influence water movement.
• Water is attracted to charged particles (sodium, calcium, etc.) due to the charges on water molecules (H2O structure).

Effects of Ion Concentration Changes

• Sodium can diffuse from plasma to interstitial fluid but not into cells.
• Excessive sweating or insensible losses increase sodium concentration in interstitial fluid.
• Increased sodium concentration in interstitial fluid pulls water from cells, causing dehydration.

Conclusion

• Maintaining fluid balance involves ensuring proper water volume and electrolyte concentration.
• Understanding movement patterns and influences is crucial for homeostasis.

Additional Information

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