Physiology Oct. 7th

Carboxylic Changes and Surface Area

  • Discussion on surface area scalability with size changes in organisms.

    • Surface area does not scale linearly with mass as organisms increase in size.

    • Rotifers are provided as an example due to their high surface area relative to mass.

Diffusion Processes

  • Nature of Diffusion

    • Gas exchange occurs through diffusion from areas of high concentration to low concentration.

    • Efficiency of diffusion is time-dependent and correlates with distance.

    • Example: Diffusion across a cell membrane (10 nanometers thick) takes about 100 nanoseconds.

    • In larger distances, such as those in larger organisms (e.g., human nerve cells), reliance on diffusion alone becomes impractical.

  • Limitations of Diffusion

    • For long distances, relying only on diffusion results in significantly delayed equilibrium, potentially affecting organism lifespan.

Comparison of Gas Exchange in Different Organisms

  • Diffusion is influenced by the type of organism: terrestrial vs aquatic.

    • Example of oxygen concentration:

    • Atmosphere holds approximately 21% oxygen.

    • Ocean has much lower oxygen concentration (~0.8%).

Physical Laws Governing Gas Exchange

  1. Ideal Gas Law (Universal Gas Law)

    • Describes how gases behave under various conditions, assuming gas molecules are perfect spheres in constant motion.

    • Involves variables like pressure (P), volume (V), and temperature (T).

    • Pressure and temperature are directly proportional (as one increases, so does the other).

    • Pressure and volume are inversely proportional (as volume decreases, pressure increases).

  2. Dalton's Law of Partial Pressures

    • Total pressure exerted by a system of gases is the sum of the partial pressures of individual gases.

    • Example notations for atmospheric gases:

    • Atmospheric pressure: 101.3 kPa at sea level.

    • Partial pressures calculated using the formula: P{gas} = f{gas} imes P_{total}

      • where ( P{gas} ) is the partial pressure, ( f{gas} ) is the fractional concentration, and ( P_{total} ) is the total pressure.

  3. Henry's Law

    • Describes the relationship between the partial pressure of a gas and its concentration in a liquid.

    • Formulated as:
      C = k_H imes P

    • where ( C ) is the concentration, ( k_H ) is the constant (which varies by gas), and ( P ) is the partial pressure of the gas.

    • Solubility varies by gas: carbon dioxide is more soluble than oxygen.

  4. Fick's Law of Diffusion

    • Governs the net rate of movement of gases through diffusion.

    • Expressed as:
      J = D imes rac{A}{d} imes (P1 - P2)

    • where ( J ) is the net diffusion rate, ( D ) is the diffusion coefficient, ( A ) is the area of diffusion, ( d ) is the distance between concentrations, and ( (P1 - P2) ) is the driving force (pressure difference).

    • Important to note that diffusion rates slow with increased distance.

Dissolution of Gases in Liquids

  • Factors affecting gas solubility:

    • Temperature: Higher temperatures lead to decreased gas solubility.

    • Salinity: Increased salinity reduces dissolved gas quantities.

Diffusion Coefficient

  • Unique for each gas and can be influenced by the medium (air vs water).

  • Diffusion occurs faster in air compared to water (10,000 times faster).

Application of Gas Exchange in Organisms

  • Gases are not just solutes; they behave differently during diffusion.

  • Example of a beetle effectively using physical laws to make oxygen move against its concentration gradient by utilizing hydrophobic air cells.

Gas Exchange Mechanisms

  • Convection vs Diffusion:

    • Convection provides additional mechanisms for rapid gas exchange compared to diffusion alone.

    • Understanding how fluids move enhances gas exchange efficiency in various systems (e.g., human lungs).

Physiological Applications

  • Organisms can control certain variables affecting diffusion rates:

    • Increasing surface area (e.g., lung alveoli).

    • Maintaining concentration gradients (e.g., keeping CO2 low in leaf interiors).

    • Minimizing distance (e.g., in capillary beds).

  • Conclusion: Essential for Gas Exchange

    • Gas exchange in complex organisms cannot rely solely on diffusion; physiological mechanisms help facilitate this process efficiently, especially in larger organisms.

  • Upcoming Lectures:

    • Focus on the anatomy and physiology associated with gas exchange in plants (specifically gaffodilian plants).