Chapter 5 Outline

Passive Solute Transport by Simple Diffusion

  • Concentration gradients give rise to the most elementary form of simple solute diffusion
  • Electrical gradients often influence the diffusion of charged solutes at membranes
  • Biological aspects of diffusion across membranes: Some solutes dissolve in the membrane; others require channels
  • Diffusion of ions across cell membranes is determined by simultaneous concentration and electrical effects
  • Diffusion often creates challenges for cells and animals
  • Concentration gradients can create electrical gradients that alter concentration gradients

Passive Solute Transport by Facilitated Diffusion

Active Transport

  • Active transport and facilitated diffusion are types of carrier-mediated transport
  • Basic properties of active-transport mechanisms
  • Recognition of active transport completes our overview of a single animal cell
  • Primary and secondary active transport differ in their cellular-molecular mechanisms
  • BOX 5.1 Energy Coupling via the Potential Energy of Electrochemical Gradients
  • Active transport across an epithelium does not imply a specific transport mechanism
  • Two epithelial ion-pumping mechanisms help freshwater fish maintain their blood composition
  • BOX 5.2 Cellular Mechanisms of Ion Pumping in Freshwater Fish Gills

Diversity and Modulation of Channels and Transporters

Osmotic Pressure and Other Colligative Properties of Aqueous Solutions

  • Physiologists usually express osmotic pressure in osmolar units
  • Osmotic pressures can be measured in several ways

Osmosis

  • Quantification and terminology
  • Hydrostatic pressures develop from osmotic pressures only when two or more solutions interact
  • Water may dissolve in membranes or pass through aquaporin water channels during osmosis
  • Aquaporins
  • Osmosis and solute physiology often interact
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