Nonpolar, hydrophobic substances diffuse much more rapidly across plasma membrane
Diffusion of Ions through channel proteins
water and charged hydrophilic solutes diffuse through channel proteins; these are lipid insoluble substances
Cells control permeability by regulating number of channel proteins
Major characteristics of diffusion pathways Yes No Chemical specificity Ions Nonpolar Typical molecules using pathway Yes No Use of integral membrane protein Through protein Channels Through lipid Bilayer
Water crosses membranes by (1) diffusion through lipid by layer and (2) diffusing through protein channels in the membrane
Osmosis is the diffusion of water from higher water concentration to lower water concentration. Osmolarity total solute concentration in the solution. The higher osmolarity of a solution the lower the water concentration.
Example: 1L solution containing 300 mOsm of non-penetrating NaCl and 100 mOsm of urea, which can cross the membrane would have a total osmolarity of 400 mOsm and would be hyperosmotic. However, it would be an isotonic solution producing no change in the equilibrium volume of cells immersed in it.
Secondary active transport properties Active (energy from ion gradient, usually Na + ) Carrier mediated Can be cotransport (symport) or countertransport (antiport) Examples (many): Na + /amino acids, Na + /glucose (luminal membrane kidney, GI tract), *Na + /H + kidney, *Ca ++ /3Na + muscle, *Cl - /HCO 3 - red cell. (* = countertransport) Kinetics see primary active transport graphs
Hyponatremia (less than 130 mEq/L)-low sodium level-may cause seizures, headache, tachycardia, hypotension, cramps, muscle twitching, irritability, decreased body temp, nausea, vomiting, and possible coma (polyuria due to diabetes insipidis may be one cause),
Hypernatremia (more than 150 mEq/L) -high sodium level-usually indicates water deficit in ECF-symptoms include thirst, tachycardia, dry sticky tongue, disorientation, hallucination, lethargy, seizures, coma, hypotension, agitation, low fever
Artial Natruretic Peptide: Regulates Na + & H2O Excretion