1. Chp 4 Transport of Solutes and Water

2. Review 1- The intracellular and extracellular fluids are similar in osmotic concentration but very different in composition - Pump and active transport maintain this state 2- Some tissues (gills) are permeable and loose ions (meant to remain) across their membranes 3- Other tissues (intestines) are exposed to high concentrations of certain solutes which they must take in (absorption)

3. Review Passive transport mechanisms transport compounds along the chemical gradient (from high to lower concentrations) In order to transport against the gradient, energy (ATP) needs to be used  active transport

4. Passive transport Simple diffusion -Factors affecting passive diffusion summarized by Fick diffusion equation (J): J= D (C1-C2)/X -(C1-C2) concentration gradient -X = Distance between the 2 regions -D = diffusion coefficient – a function of temperature, membrane permeability to the compound and surface of diffusion (compounds that do not cross the phospholipid bilayer will need channels) -The electrical gradients also affect the diffusion

5. Biological aspects of diffusion Lipid-soluble compounds will cross the phospholipid bilayer driven by their gradient (lipids, gases, H 2 O and small, neutral compounds such as urea) All other compounds (not small enough and/or charged) will need a channel and/or transporter to cross the cell membrane The diffusion of ions across cell membrane is determined by simultaneous concentration and electrical effects

6. Donnan equilibrium Ions diffuse across the cell membrane according to their chemical and electrical gradients. In doing so, they modify the electrical and osmotic forces This, in turn, triggers the movement of other compounds across the membrane Movement of ions and compounds will occur until osmotic and electrical equilibrium Overall, compartments are electrically Neutral!! Charge differences arise when ions are separated (ex: by the cell membrane)

7. Somebody who does not want to cross!

8. Facilitated diffusion Charged (ions) or large (amino acids, monosaccharides and larger) molecules need channels or carrier protein in order to enter the cell. Channels are always open to a particular solute Carrier proteins are more specific and must fit to the solute before allowing to pass through

9. Active transport The transport is always against gradient, thus needs energy (ATP) Primary active transport: use ATP directly: –Na+-K+ ATPase pump –Ca++ ATPase –H+-K+ ATPase –H+ ATPase Secondary active transport: –Draw energy from an electrochemical gradient created by an ATPase pump –Examples?

10. The Na-K pump Expels 3 Na+ for every 2 K+ imported Maintain an electrochemical gradient across the membrane K+ is about x100 more permeable than Na+  membrane potential (- 70mV) near K+ potential (-90mV)

11. Secondary active transport is used in a few system such as digestion Na+ K+ ATPase is located on the apical side Other transporters (or countertransporters) are located on the basolateral side

12. Possible means of carrying glucose across the intestinal lining

13. Secondary active transport Retrieval of Na+ by gill epithelium in fresh water fish

14. Summary of cell transport

15. Modulation of channels and transporters Modulation of gene expression Multiple molecular forms Noncovalent and covalent modulation Insertion-and-retrieval modulation

16. Colligative properties of aqueous solution: Osmotic pressure Osmotic pressure is created by the presence of non permeable solutes present in one compartment only.