Anatomy & Physiology: Passive Transport PDF

Anatomy & Physiology: Passive Transport Dr. Heather Jones [email protected] 866-8133  Transport Passive transport: does not require energy Simple Diffusion Facilitated transport Active transport: requires energy Primary active transport Secondary ac...

Anatomy & Physiology: Passive Transport Dr. Heather Jones [email protected] 866-8133  Transport Passive transport: does not require energy Simple Diffusion Facilitated transport Active transport: requires energy Primary active transport Secondary active transport  Diffusion Simple Diffusion: movement of molecules from one place to another based on their random thermal motion Net flux direction determined by gradient Diffusion equilibrium: equal movement in both directions Diffusion  Diffusion Simple Diffusion: no carrier needed Molecule is permeable to the lipid bilayer Fatty acids, gases, steroids  Diffusion Facilitated Diffusion: requires a membrane protein 1. Ion Channels Ions are impermeable to the lipid bilayer Specific channels Many are gated (ligand, voltage, stretch)  Diffusion Gating and selectivity: Potassium channel example  Diffusion Facilitated Diffusion: requires a membrane protein 2. Carrier-mediated From high to low concentration Highly specific Requires binding of molecule to carrier and conformational change  Diffusion Carrier mediated : classic example of the GLUT transporters What if the glucose concentration was higher inside the cell, how would the transporter work?  Diffusion Flux of solutes: simple passive versus facilitated diffusion ✔ Where do channels belong?  Osmosis Osmosis: the passive diffusion of water from one side of a selective barrier (membrane) to the other Aquaporin channels increase the movement of water (polar molecule) Movement of water based on number of particles present Water moves down its concentration gradient Osmolarity: concentration of osmotically active particles in a solution (Osm/L) Posm = n * C * RT 150 mM NaCl = ? Osm/L n = number of particles (ex. NaCl = 2 Osm) C = concentration  Osmosis Net water movement is ONLY determined by the concentration of impermeable solutes: osmotic pressure Ions Large molecules Molecules which move by facilitated (ungated) transporters or can easily pass though the membrane will not generate an osmotic pressure Osmotic pressure (π) = φ n * C* RT φ = a permeability factor, permeable molecules cannot generate an osmotic pressure so φ = 0, impermeable molecules have a φ closer to 1.  Osmosis Water movement: non-penetrating solutes determine direction of water movement  Osmosis Tonicity: ability of a solution to cause a cell to shrink or swell Isotonic: solution has the same number of non-penetrating solutes as the intracellular compartment Hypertonic: Hypotonic: