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ESS_40_Lec_3_2009

ESS_40_Lec_3_2009 - Lecture Outline 1 Lecture 3(Chp 3...

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9/27/2009 1 1 Lecture 3 (Chp 3) Interactions Between Cells & the Extracellular Environment Lecture Outline • Extracellular Environment • Movement Across Plasma Membrane • Osmosis • Membrane Transport Systems • Membrane Potential • Cell Signaling 2 Extracellular Environment 3 Extracellular Environment • Includes all constituents of body outside cells • 67% of total body H 2 0 is inside cells (= intracellular compartment-ICF ); • 33% is outside cells (= extracellular compartment-ECF ) – 20% of ECF is blood plasma – 80% of ECF is interstitial fluid contained in gel-like matrix 4
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9/27/2009 2 Movement Across Plasma Membrane 6 Transport Across Plasma Membrane • Plasma membrane is selectively permeable -- allows only certain kinds of molecules to pass • Many important molecules have transporters & channels – Carrier-mediated transport involves specific protein transporters – Non-carrier mediated transport occurs by diffusion 7 Transport Across Plasma Membrane continued • Passive transport moves compounds down concentration gradient; requires no energy • Active transport moves compounds up a concentration gradient ; requires energy & transporters 8
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9/27/2009 3 Diffusion • Is random motion of molecules – Net movement is from region of high to low concentration 9 Diffusion continued Diffusion depends on the random movement of molecules. By net diffusion molecules move down their concentration gradient. Net diffusion tends toward a steady state . Diffusion can occur through a permeable membrane. – Substances can pass through a lipid bilayer or channel. 10 Diffusion continued • Non-polar compounds readily diffuse thru cell membrane – Also some small molecules including C0 2 & H 2 0 • Diffusion of H 2 0 is called osmosis • Cell membrane is impermeable to charged & most polar compounds – Charged molecules must have an ion channel or transporter to move across membrane 11 Diffusion continued • Rate of diffusion depends on: – Magnitude of its concentration gradient – Permeability of membrane to it – Molecular weight – Surface area of membrane – Thickness of the membrane **Fick’s Law of Diffusion 12
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