1. Chapter 4 Transport of Substances Through Cell Membranes Dr. Marko Ljubković Department of Physiology 1

2. Cell membrane Lipid bilayer Phospholipids (25%), Proteins (55%), Cholesterol (17%) and Carbohydrates (3%) Hydrophilic and hydrophobic part 2

3. Extracellular and intracellular fluid 3

4. Transport across the membrane Passive (diffusion) – kinetic energy Active – requires additional energy source 4

5. Simple diffusion 1.Through lipid bilayer (lipid soluble: O 2, CO 2, N 2, alcohol) 2.Through protein pores and channels (H 2 O, urea, ions) 5

6. Ion channels Integral membrane proteins Selectivity Gating Voltage Ligand Pressure Recorded by patch- clamp technique 6

7. Facilitated diffusion Requires protein carriers Slower than simple diffusion Glucose, aminoacids 7

8. Factors that determine diffusion 1.Concentration difference 2.Membrane electrical potential (Nerst equation) 3.Pressure difference 8

9. Active transport across the membrane 1.Primary active (directly from energy-rich substrate: ATP) NaK pump, Ca ATPase, H ATPase 2.Secondary active (energy stored in form of electrochemical gradient) Co-transport (glucose) Counter-transport (NaCa exchanger, NHX) NaK ATPase NaGlu Transporter

10. Osmosis Diffusion of solvent through semi-permeable membrane Osmotic pressure Osmolality – concentration of osmotically active particles (glucose vs. NaCl) 10

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