Anatomy and phys lecture 8
Anatomy and phys lecture 8 PHCL2600
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This 6 page Class Notes was uploaded by Legacy Tanner on Tuesday October 6, 2015. The Class Notes belongs to PHCL2600 at University of Toledo taught by Williams,F in Fall 2015. Since its upload, it has received 40 views. For similar materials see Funct Anat and Pathophysiol I in Pharmaceutical Sciences at University of Toledo.
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Date Created: 10/06/15
Anatomy Lecture 8 Water Diffusion 0 Water can diffuse across a membrane quite easily yet it is a small polar molecule 0 Diffuses through the lipid region possibly doing this by associating with fatty acids 0 Also crosses through in channels Na K because these are hydrated when they cross the membrane so water goes through as well 0 Aquaporins small channels just for water Osmosis o The diffusion of water across a membrane 0 More speci cally diffusion of a solvent across a membrane into an area of higher concentration of solute o Membrane needs to be relatively impervious to solute therefore no net movement of solute across membrane 0 Review 0 We are interested in osmosis across a cell membrane so remember 2 uid compartments separated by cell membrane Intracellular uid ICF all uid inside cell Extracellular uid ECF a uid outside cell 0 ICF mostly K some Mg2 PO43 proteins and organic ions anything carbon based with a charge o ECF mostly Cl Na some Ca2 and HCO3 little to no protein 0 All molecules contribute to the total solute concentration this is referred to osmolarity Osmolarity 0 Number of moles of total solutes dissolved in 1 liter of water 1 Osm or 1 Osmolar o Molarity differs as it is the weight of solute dissolved where osmolarity is based on the number of molecules 0 1 molar solution of NaCl is actually 2 osmolar because there are 2 atoms when NaCl dissociates 0 Contribution to osmolarity Total concentration of all solutes independent of chemical nature is what drives osmosis of water across a membrane this is assuming ideal conditions Osmolarity of ECF is approximately 300 mOsm milli Osmolar Osmolarity of ICF at equilibrium is also approximately 300 mOsm 0 Effective impermeability Most solutes outside of cell ECF are Na and Cl membrane is effectively impermeable to these Most solute inside the cell ICF is K membrane is effectively impermeable to this How Even though they do freely cross the membrane by diffusion through channels or carriers the cell has proteins in the membrane that pump them back to where they came from thus effectively impermeability Basically they still move across but the net change is almost 0 Tonic anyone 0 lsotonic a solution which has the same osmolarity as the ECF and contains solutes that effectively do not cross the membrane 0 Hypertonic a solution has greater than the 300mOsm osmolarity result is the water within cell will leave for the outside and crush or crenate the cell 0 Hypotonic a solution has less than the cell s 300mOsm osmolarity results in water rushing into cell and cell explodes or lyses lsotonic uids must be given intravenously in order to minimize damage to the blood cells 0 Picture of mini quiz 1 question in phone 0 Carrier mediated transport 0 2 kinds Facilitated diffusion energy not required dependent on chemical gradient for diffusion continues until equilibrium is reached protein mediating transport will bind molecule with equal affinity at either side of membrane 0 Example glucose into tissues adipose muscle Active transport transport occurs against a gradient concentration or electrical thus the cell must expend energy to do this 0 Energy is in the form of hydrolysis of ATP adenosine triphosphate ATP H20 a ADP Pi 7 kilocalories energy NaK ATPase pump 0 0 Example of active transport system Because Na and K can diffuse through channels in the membrane one would expect that they could and would eventually reach equilibrium same concentration on both sides of membrane however this isn t the case The typical cell has 5mM K in the ECF That concentration is closer to 150mM in the ICF producing quite a gradient Similarly Na has a concentration of 150mM in the ECF and 15mM in the ICF You would expect passive diffusion or facilitated diffusion at lease to bring these to equilibrium inside The reason that this does not happen equilibrium is simple recall that the ICF is also relatively negative in nature proteins and organic anions The passive diffusion of K into the cell down an electrical gradient is almost equal to that out of cell down a concentration gradient active transport maintains the gradient as is Same with Na active transport out is roughly equal to diffusion into the cell down the concentration and electrical gradients In rats as a model of all mammals there are about 150000 sodium pumps per small intestine enterocyte which collectively allow each cell to transport about 45 billion sodium ions out of each cell per minute 0 The pump itself A cluster of 2 protein subunits in the membrane Pump acts as a carrier transporting Na and K but also acts as an enzyme which cleaves ATP to ADP ATPase Pump accounts for about 30 of energy used by the average cell maybe 6070 in neurons Transport of Na is coupled to K 3 Na move out of cell for every 2K that move into cell 0 creates a charge eectrogenic creates a negative charge inside cell 0 Sequence of events ATP binds to ATPase site on ICF side at same time as 3 Na bind ATP is hydrolyzed to ADP by ATPase and pump is phosphorylated Conformational change occurs 3 Na moved to ECF side and released 2 K bind on ECF side and dephosphorylation of pump occurs conformational change to previous conformation 2K are released to ICF 0 Secondary active transport Symport or antiport 1 solute moves down a gradient at the same time as another Symport same direction Antiport different direction Energy for 1 molecule s transport is generated by the other s movement no ATP is directly required but ATPase maintains the gradient 0 Other active processes endocytosis Phagocytosis to eat a cell large external particle is taken in engulfed by a portion of plasma membrane Pinocytosis to drink a cell similar to phagocytosis except particle is often just a solute Receptor mediated endocytosis selective process substance bind to receptor and coated pits are formed to drag contents in
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