Biophysics: Test Yourself and Learn with Dr. Abdel Aziz M. Hussein

1. بسم الله الرحمن الرحيم ﴿و ما أوتيتم من العلم إلا قليلا﴾ صدق الله العظيم الاسراء اية 58

2. BIOPHYSICS By Dr. Abdel Aziz M. Hussein Lecturer of Medical Physiology Member of American Society of Physiology

3. Test Yourself • Na+ - K+ ATPase is inactivated by which of the followings : • a) high intracellular [ Na+ ] . • b) high extra cellular [K+] . • c) availability of ATP . • d) cardiac glycosides . • e) thyroxin hormone . Biophysics , Abdelaziz Hussein

4. Test Yourself • Solute movement by active transport can be distinguished from solute transport by facilitated diffusion because active transport; • Is saturable at high solute concentration • Is inhibited by other molecules with structures similar to that of the solute • Moves the solute against its electrochemical gradient • Allows movement of polar molecules Biophysics , Abdelaziz Hussein

5. Test Yourself • A sodium channel that opens in response to change in membrane voltage is an example of • A ligand-gated ion channel • An ion pump • A voltage -gated ion channel • A peripheral membrane protein Biophysics , Abdelaziz Hussein

6. Test Yourself • The Na-K pump is • A peripheral protein. • An integral protein. • A glycolipid. • A phospholipid. Biophysics , Abdelaziz Hussein

7. Osmosis Biophysics , Abdelaziz Hussein

8. Water Channels (Aquaporins) Peter Agre 2003 Nobel Prize, Chemistry

9. Osmosis Solute Water

10. Osmosis • It is the passive flow of water across a semi-permeable (selectively permeable) membrane down a concentration gradient of water i.e. • From high concentration of water to low concentration of water or • From low concentration of solute to high concentration of solute Biophysics , Abdelaziz Hussein

12. Osmolarity and Osmolality Osmolarity • It is the number of osmoles per one liter of solution. Osmolality • It is the number of osmoles per one Kg of solvent. Biophysics , Abdelaziz Hussein

13. Significance of Osmosis At Cellular Level At Capillary Level Biophysics , Abdelaziz Hussein

14. Significance of Osmosis a) At the cellular level The ECF and ICF are osmotically equal and any change in plasma osmolarity causes cells to shrink or swell Plasma osmolarity • 290 mosmol/L ICF= 290 mosoml/L ICF= 290 mosoml/L ICF= 290 mosoml/L Osmolarity = 290 mosoml/L Biophysics , Abdelaziz Hussein

15. Significance of Osmosis Tonicity • It is the ability of a solution to affect fluid volume and pressurewithin a cell. • It depends on concentration and permeability of solute • It is a property of a solution in reference to particular membrane. Biophysics , Abdelaziz Hussein

16. Tonicity • Solutions are 3 types according to its tonicity Biophysics , Abdelaziz Hussein

17. a) Isotonic Solution Isotonic solution has the same osmolarity as plasma and causes no change in cell volume e.g. NaCl solution 0.9 %

18. b) Hypotonic Solution • Hypotonic solution has osmolarity less than the plasma which causes drawing water into the cell resulting in cell swelling

19. c) Hypertonic Solution • Hypertonic solution has osmolarity higher than the plasma which causes drawing water out of the cell resulting in cell shrinkage

20. Significance of Osmosis • Hyperosmolarity can cause coma • Hyposmolarity can cause convulsions • When the cell is exposed to hypotonic fluid it will swell → activates channels in the cell membrane → allow increased efflux of K, Cl and organic anions, and small organic solute → water follows these osmotically active particles out of the cell → the cell resumes its original volume. Biophysics , Abdelaziz Hussein

21. Calculation of Cell Volume Any change in the cell volume due to change in ECF osmolarity can be calculated from the following equation; Biophysics , Abdelaziz Hussein

22. Significance of Osmosis Hydrostatic Pressure Osmotic Pressure Water and dissolved molecules Water and dissolved molecules

23. Significance of Osmosis b) At the capillary level Plasma proteins account for about 1.2 mosml/L of the total plasma osmolarity (290 mosm/L) create an osmotic pressure about 25 – 28 mmHg, called the colloid oncotic pressure, which draws water from interstitial fluid to the capillaries Osmotic Pressure

24. Osmotic Pressure Definition It is the pressure needed to prevent solvent migration (osmosis). Measurement Osmotic Pressure Water Albumin

25. Osmotic Pressure Hydrostatic Pressure Osmotic Pressure

26. Donnan Equilibrium

27. Donnan Equilibrium Na+ = Cl - = Protein = = Na+ ( 150 meq/L) Cl - (125 meq/L) Na+ ( 150 meq/L) Organic anions (25 meq/L) Cl - (150 meq/L) Chemical gradient

28. Donnan Equilibrium Na+ = Cl - = Protein = = Na+ ( 156.5 meq/L) Cl - (131.5 meq/L) Na+ ( 143.5 meq/L) Organic anions (25 meq/L) Cl - (143.5 meq/L) +++++++++ _ _ _ ______ Chemical gradient Electrical gradient

29. Donnan Equilibrium Definition: • Equilibrium that is achieved when 2 solutions containing several ions separated by a membrane permeable to several ions, but not all of the ions.

31. Donnan Equilibrium Effects : • 1. A potential energyis established on the membrane due to the presence of nondiffusable anions on one side of the membrane → to balance the concentration gradient for any ions

32. Donnan Equilibrium Effects : [Na+]1 2) The diffusable ions arrange themselves so that their concentrations ratios are equal [Cl-]2 = [Cl-]1 [Na+]2

33. Donnan Equilibrium Effects : 3) The osmotically active particles on the side of nondiffusable anion are greater than that of the other side → there is osmotic dysequilibrium Na+ (143.5 meq/L) Cl - (143.5 meq/L)

34. Significanceof Donnan equilibrium At Cellular Level At Capillary Level Biophysics , Abdelaziz Hussein

35. Significance of Donnan Equilibrium a) At the level of cells • Donnan equilibrium tends to cause osmotic dysequilibrium due to the presence of nondiffusable protein anions inside the cell→ osmosis of water inside the cell. • This is prevented by Na-K pump→ maintain low intracellular Na concentration → keep the inside and outside in osmotic equilibrium.

36. Significance of Donnan Equilibrium b) At capillaries: • Donnan equilibrium occurs in the capillaries due to the presence of nondiffusable plasma protein inside the capillaries, so; • Na concentration is slightly more in the blood than in the interstitial fluid → ↑ osmotically active particles in blood. • Cl concentration is relatively less in the blood than in the interstitial fluid.

37. Significance of Donnan Equilibrium c) At glomerular capillaries: • Donnan equilibrium causes glomerular filtrate to contain less Na and more Cl relative to plasma.

40. THANKS