صدق الله العظيم الاسراء اية 58

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

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. 3 Biophysics, Abdelaziz Hussein

Test Yourself Solute movement by active transport can be distinguished from solute transport by facilitated diffusion because active transport; 1.Is saturable at high solute concentration 2.Is inhibited by other molecules with structures similar to that of the solute 3.Moves the solute against its electrochemical gradient 4.Allows movement of polar molecules 4 Biophysics, Abdelaziz Hussein

Test Yourself A sodium channel that opens in response to change in membrane voltage is an example of 1.A ligand-gated ion channel 2.An ion pump 3.A voltage -gated ion channel 4.A peripheral membrane protein 5 Biophysics, Abdelaziz Hussein

Test Yourself The Na-K pump is 1.A peripheral protein. 2.An integral protein. 3.A glycolipid. 4.A phospholipid. 6 Biophysics, Abdelaziz Hussein

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

Solute 9 Water

10 Biophysics, Abdelaziz Hussein 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

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

13 Biophysics, Abdelaziz Hussein At Cellular LevelAt Capillary Level

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

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

16 Biophysics, Abdelaziz Hussein Solutions are 3 types according to its tonicity Solution Isotonic solution Hypertonic solution Hypotonic solution

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

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

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

20 Biophysics, Abdelaziz Hussein  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.

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

Water and dissolved molecules Hydrostatic Pressure Osmotic Pressure

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

Osmotic Pressure Hydrostatic Pressure

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

Na+ = Cl - = Protein = = Organic anions (25 meq/L) Cl - (131.5 meq/L) Na+ ( meq/L) Cl - (143.5 meq/L) Na+ ( meq/L) __________________ Chemical gradient Electrical gradient

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.

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Effects : 1. A potential energy is 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

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

3) The osmotically active particles on the side of nondiffusable anion are greater than that of the other side → there is osmotic dysequilibriumIII Na+ (156.5 meq/L) Cl - (131.5 meq/L) Organic anions (25 meq/L) Na+ (143.5 meq/L) Cl - (143.5 meq/L)

34 Biophysics, Abdelaziz Hussein At Cellular LevelAt Capillary Level

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.

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.

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

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