صدق الله العظيم الاسراء اية 58

By Dr. Abdel Aziz M. Hussein Lecturer of Medical Physiology

Test Yourself Which of the following best describe the process of diffusion : a) A " downhill " process. b) An " uphill " process. c) A process by which only large molecular weight proteins may move across biological membrane. d) require metabolic energy. e) depends on the balance between hydrostatic pressure and oncotic pressure of plasma protein 3 Biophysics, Abdelaziz Hussein

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5 Lumen Epithelium Luminal or apical border Basolateral border

Apical membrane Basolateral membrane Tight Junctions

7 Lumen Capillary H2O Na

8 Lumen Capillary H2O Na

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11 Lumen Capillary

12 Impulse

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Gated ion channels Voltage gated ion channels Ligand gated ion channels 14

15 Biophysics, Abdelaziz Hussein Receptor Gate LigandIon

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Def., Channels are closely associated with a membrane receptors Mechanism: When the chemical agent binds to its receptor, it causes a conformational change in the channel →open the channel 19 Biophysics, Abdelaziz Hussein

Selectivity: nonselective ion channels i.e. conduct more than one type of similarly charged ions 20 Biophysics, Abdelaziz Hussein

Example: Cholinergic receptor at the motor end plate of sk. Ms → permits the passage of Na into and K out of the ms cell Important in generation of motor end plate potential 21 Biophysics, Abdelaziz Hussein

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23 Biophysics, Abdelaziz Hussein Gate Ion

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Def., Channels open by changes in cell membrane potential Mechanism When the membrane potential reach certain level→ triggers the movement of +vely charged amino-acids in the α- subunits which form the ion conducting shaft of the channel→ cause conformational change in the channel→ open it 27 Biophysics, Abdelaziz Hussein

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Selectivity: ion selective channel i.e. conduct only one ion Example: Voltage gated Na, K and Ca channels Important in generation of action potential 29 Biophysics, Abdelaziz Hussein

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Def It is the diffusion of substances across the cell membrane (down electrochemical gradient) which needs the presence of carrier proteins→ carrier mediated diffusion. 32 Biophysics, Abdelaziz Hussein

Mechanisms: When the substance binds to its transport carrier protein→ it undergoes a reversible conformational change→ it transports the substance across the membrane down its concentration gradient. 33 Biophysics, Abdelaziz Hussein

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Rate Is limited because it depends on the availability of a definite No. of carrier proteinsCharacters 1) It occurs down an electrochemical gradient 2) It is passive i.e. no energy is required. 3) It requires the presence of a transport carrier protein. 35 Biophysics, Abdelaziz Hussein

Characters 4) It is rate-limiting and saturable because it depends on the availability of a definite number of carrier or channel proteins 36 Biophysics, Abdelaziz Hussein

Example: Glucose transporters (GLUT) which transports glucose into RBCs, ms cells and adipose tissue 37 Biophysics, Abdelaziz Hussein

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Diffusion Fick’s Law of diffusion- M = Ds. A.  C x diffusion animation Adolph Fick

The important to the cell (for a substance diffuse in both directions) is not the total substance diffusing in both directions but the difference between these two (net rate of diffusion in one direction). 40

Factors affecting net rate of diffusion Factors affecting net rate of diffusion 1.Concentration gradient for the solute. 2.Diffusion Coefficient or permeability coefficient of the membrane. 3.Membrane surface area. Rate of diffusion is directly proportional to these factors. 4. Membrane thickness or distance, the rate of diffusion is inversely proportional to the thickness of the membrane. 41

Fick's law:Fick's law: 42 D = diffusion coefficient. A = area of membrane (cm2). X = thickness of the membrane (cm). C in and C out = the concentration of the material on the inside and outside of the membrane, respectively (mmol/L or mmol/cm3). The -ve sign indicates that the material is moving down its concentration gradient

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44 Biophysics, Abdelaziz Hussein Low concentration High concentration ATP

45 Abdelaziz Hussein Def., Is the movement of substances across the cell membranes against an electrochemical gradient. Types: Active transport PrimarySecondary

46 Abdelaziz Hussein 1) Primary active transport → obtain its energy directly from the hydrolysis of ATP e.g. Na-K Pump, Ca ATPase, H-K ATPase 2) Secondary active transport → use the energy stored in the Na concentration gradient e.g. Na- glucose co-transport and Na-Ca exchange

Na+ ICF ECF K+ Na+ Glucose K+ = 4 mEq/L Na+= 140 mEq/L K+ = 140 mEq/L Na+= 14mEq/L High glucose Low Glucose ATP ADP

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49 Abdelaziz Hussein 2) Characters: 1.Occurs against the electrochemical gradient 2.Active i.e. energy is required. 3.Requires the presence of a transport carrier protein→ so exhibits;  Stereospecificity  Saturation  Competition  Rate limiting

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Differences ( ) simple diffusion, facilitated diffusion and active transport 51 Abdelaziz Hussein Simple diffusionFacilitated diffusionActive transport Electrochemical gradient Downhill Uphill Energy Doenot need energy Needs energy Rate Not limitedLimited Saturation Not SaturableSaturable Carrier Doenot need carrierNeeds carrier Competition Not show competitionShows competition Stereospecificity Does not depend on Stereospecificity Depends on Stereospecificity

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THANKS