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