Chapter 2

• Diffusion coefficient

  The ability for a medium to dissolve into another medium
• Higher diffusion coefficient = more soluble (the better diffusion), lower diffusion coefficient = less soluble
• Solubility complies with concentration
• O2 in the aquatic environment

  • Lower diffusion rate
  • Lower solubility
  • Less available O2 in given volume of fluid
• Animals use more energy to run an O2 "pump" or need a more efficient O2 "pump" in water
• Fick's first law

  Solute will move from a region of high concentration to a region of low concentration across a concentration gradient
• Concentration gradient

  Source of potential energy
• Voltage gradient

  Electrical potential + membrane potential
• Fick's second law

  The amount of substance diffuses across a surface is proportional to the area of that surface and inversely proportional to the distance across which it diffuses
• Application of Fick's second law: circulation (how long/wide your arteries are)
• O2 is proportional to pO2 at constant temperature
• Amount of O2 that dissolves in liquid is determined by pO2 and solubility of liquid
• X

  Longer = longer diffusion rate
• MW

  Longer = longer diffusion rate
• P

  p2 (end) - p1 (initial)
• External respiration

  • Ventilation - active movement of respiratory medium
  • Perfusion: gas uptake
• Internal respiration

  Use of O2 to make energy
• Scaled down: SA:V large, X and A is not a problem, simple diffusion works well
• Scaled up: SA:V Small, X and A must improve oxygen uptake, need specialized structures (e.g. gills or lungs)
• Blood reaching the respiratory system is oxygen-poor and leaving oxygen-rich
• Blood is moving in the opposite direction of water
• Carbon dioxide molecules in blood diffuse from the blood (high concentration) to water (low concentration)
• Gills

  • Thin tissue filaments that are highly branched and folded
  • Gill arch (larger blood vessels)
  • Gill filaments (smaller blood vessels)
  • Gill lamellae (capillaries)
• Respiration in water

  1. When water passes over gills, the dissolved oxygen in water rapidly diffuses across gills into bloodstream

  2. Circulatory system carries the oxygenated blood to other parts of body
• Some animals contain body cavity (coelom), which is filled with coelom fluid needed for gas exchange and locomotion
• In this case, oxygen diffuses across gill surfaces and into coelomic fluid instead of blood
• Found in mollusks, annelids, and crustaceans
• Unidirectional flow

  Medium enters at one point and exits at another
• Counter-current flow

  In fish gills
• Concurrent flow

  Diffusion gradient is not as efficient or disappears
• Spiracular Breathing

  Unidirectional flow: from spiracles to abdomen and then out through different set of spiracles
• Spiracles

  • External respiratory openings in exoskeleton
  • Able to dilate (open and close), changes partial pressure
  • Control air flow into trachea
  • Control water loss
  • Keep dust out
• Dalton's Law: Total pressure is the sum of all particle pressures of a gaseous mixture
• Atmospheric pressure is 1atm, which is the sum of the particle pressures of nitrogen, oxygen, water, CO2, and some other gases
• Partial pressure (Px)

  The pressure of a single gas in a mixture
• Dalton's law states that each gas in a mixture exerts its own pressure, contributing to the total pressure
• Boyle's Law

  Gases move from areas of high pressure to areas of low pressure, and the pressure of a gas is inversely proportional to the volume of its container
• Henry's Law

  The concentration of gas in a liquid is directly proportional to the solubility and partial pressure of that gas
• The partial pressure of oxygen or CO2 is directly proportional to the concentration of these gases in blood
• Different gases make up different parts of the air, and each gas has its own pressure within the mix, adding up to the total atmospheric pressure