Physiology MD137: Fluid Compartments Quiz

Course Information

• Course: Physiology
• Module: MD137
• Year: 2024-2025
• Lecturer: Dr. Karl McCullagh
• Reading: Vander 15th edition, Chapter 4
• University: University of Galway

Learning Outcomes

• Students will learn about the fluid compartments of the body, their composition, properties (including osmolarity and pH), and their clinical significance.

Lecture Outline

• Fluid intake and output are balanced during steady-state conditions
• Body fluid compartments
• Constituents of extracellular and intracellular fluids
• Measurement of fluid volumes: principles and specific fluid compartments
• Regulation of fluid exchange and osmotic equilibrium between intracellular and extracellular fluid
• Hyponatremia and hypernatremia

Body Fluid Compartments

• 40% of body weight is intracellular fluid (28.0 L)
• 20% of body weight is extracellular fluid (14.0 L)
  • Plasma: 3.0 L
  • Interstitial fluid: 11.0 L
  • 4% plasma (non-cellular)
  • 1% transcellular

Constituents of Body Fluids

• Proteins and related substances (18%)
• Minerals (7%)
• Fat (15%)
• Water (60%)

Fluid Balance (70 kg adult)

• Intake (ml/day):
  • Fluids ingested: 2100 ml
  • From metabolism: 200 ml
  • Total: 2300 ml
• Output (ml/day):
  • Insensible (skin): 350 ml
  • Insensible (lungs): 350 ml
  • Sweat: 100 ml
  • Feces: 100 ml
  • Urine: 1400 ml
  • Total: 2300 ml

Fluid Balance (70 kg adult) - Heavy Exercise

• Intake (ml/day):
  • Fluids ingested: 6400 ml
  • From metabolism: 200 ml
  • Total: 6600 ml
• Output (ml/day):
  • Insensible (skin): 350 ml
  • Insensible (lungs): 650 ml
  • Sweat: 5000 ml
  • Feces: 100 ml
  • Urine: 500 ml
  • Total: 6600 ml

Body Fluid Volumes

• Total body water (TBW): 45 L
• Extracellular fluid (ECF): 15 L
• Intracellular fluid (ICF): 30 L
  • Plasma: 3.5 L
  • Interstitial fluid: 8.5 L
  • Lymph: 1.5 L
  • Transcellular fluid: 1.5 L

Ionic Composition

• Extracellular Fluid (mmol/L):
  • Na+: 145
  • K+: 5
  • Ca2+: 2.5
  • Mg2+: 1.0
  • Cl-: 102
  • HCO3-: 28
  • PO4: 1.3
• Intracellular Fluid (mmol/L):
  • Na+: 12
  • K+: 155
  • Ca2+: 0.5
  • Mg2+: 15
  • Cl-: 4
  • HCO3-: 8
  • PO4: 73

Units

• Molar Solution: One mole of a substance dissolved in enough water to make one liter of solution
• Molal Solution: One mole of a substance dissolved in one kilogram of water
• Equivalents (mEq): Equal to the molarity multiplied by the charge number; a measure of charge concentration
  • 150 mMolar Na+ = 150 mEq/L
  • 50 mMolar Ca2+ = 100 mEq/L

Measuring Body Fluid Volumes: Indicator Dilution Principle

• Indicator Mass A = Volume A x Concentration A
• Indicator Mass A = Indicator Mass B
• Indicator Mass B = Volume B x Concentration B
• Volume B = Indicator Mass B / Concentration B

Question Examples

• Question regarding total body water measurement: Calculate total body water given an injected volume, concentration, and concentration after equilibrium.
• Question regarding interstitial fluid measurement: Name the two substances best suited to measure interstitial fluid volume.
• Question regarding 3% NaCl solution: Determine osmolarity and tonicity of 3% NaCl solution
• Question regarding 5% glucose solution: Determine osmolarity and tonicity of 5% glucose solution
• Questions regarding effects of water administration: Predict resulting changes in extracellular fluid volume, osmolarity, intracellular fluid volume, and intracellular fluid osmolarity upon water administration.

This quiz focuses on fluid compartments of the body, including their composition and clinical significance as covered in Vander's 15th edition, Chapter 4. You'll explore key concepts such as osmolarity, pH, and the regulation of fluid exchange. Test your understanding on the percentages of body fluids and conditions like hyponatremia and hypernatremia.