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40 Cards in this Set
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- Back
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Diffusion
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process of net mvmt of one type of molecule through space as a result of random motion (Entropy)
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Process by which molecules intermingle as a result of their kinetic energy of random motion
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diffusion
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Rate of diffusion can be increased with
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an increase in thermal energy
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The rate of diffusion can be slowed by
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increasing the thickness of the membrane and/or incr size of molecules
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How does the alveolar membrane illustrate diffusion through a permeable membrane?
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higher O2 on alveolar side drives net mvmt to capillary side
continuous capillary blood flow causes O2 to be removed maintaining gradient movement secondary to the area of higher concentration on the alveolar side |
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How do osmotic/oncotic pressures illustrate diffusion through a semi-permeable membrane?
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water is freely permeable and attempts to distribute equally, so that it may dilute the concentration gradient equally, proteins cannot bc are too large to pass
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What happens if 2 solutions of different concentrations are separated by a semi-permeable membrane which is permeable to the smaller solvent molecules but not to the larger solute molecules?
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solvent will tend to diffuse across the membrane from the less concentrated to the more concentrated soln -- OSMOSIS
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Osmosis is of great biological importance when the solvent is ___.
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water
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Osmotic pressure
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selective diffusion process driven by internal energy of the solvent molecules
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If pure water were on both sides of a membrane, the osmotic pressure would be ____. If normal human blood were on one side and water on the other, the osmotic pressure would be ___.
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0, 7 atm
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Choosing to admin a colloidal soln instead of a crystalloid is based on the goal to...
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keep the fluid intravascular for a longer period of time
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Osmotic pressure is related to teh number of ...
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non-permeable molecules (Solute)
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____ is the pressure required to stop osmosis.
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osmotic pressure
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Oncotic pressure
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in capillaries, osmotic pressure caused by plasma proteins
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Osmolarity
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a mole of any solute in 22.4 L of solution at 0 deg C will exert an osmotic pressure of 1 atm.
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In a mixed solution, the osmotic pressure is the sum of
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the individual molarities
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Over 99% of plasma osmolarity is due to _____. _____ account for approx 1 milliosmole/L.
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electrolytes, plasma proteins
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RBCs lyse at osmolarities below ____.
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200 mosm/L
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Capillaries are impermeable to plsama proteins and this causes an osmotic pressure difference between _____ and ____.
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plasma, interstitial fluid
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Normal oncotic pressure
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24-27 mmHg
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What are the requirements for osmosis across cell membranes?
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must have membrane that is impermeable to one or more solutes
must have difference in concentration of solutes |
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What are the requirements for osmosis across capillary walls?
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most capillary walls are permeable to small solutes (Na, Cl)
albumin doesn't permeate the capillary wall |
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Ficks Law of Gas Diffusion Equation
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J ={ (solubility constant for O2 x diffusivity) / (membrane thickness) } x (PaO2 - Pulm capillary O2 partial pressure)
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According to Fick's Law, diffusion rate of a gas is directly proportional to:
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- partial pressure gradient
- membrane area - solubility of gas in membrane |
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According to Fick's Law, diffusion rate of a gas is inversely proportional to:
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- membrane thickness
- square rt of molecular wt |
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What are the applications of Fick's Law in gas diffusion?
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- concentration effect
- second gas effect - diffusion hypoxia - N20 accumulation in closed spaces |
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When a semi-permeable membrane is permeable to one ion but not the other oppositely charged ion, a ______ is produced. This transmembrane potential can be calculated by the _______ equation.
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a charge imbalance is produced -- transmembrane potential can be calc by Nernst Equation
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What is an applicable example of the Nernst equation?
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the re-establishment of trans-membrane potential after depolarization and impulse transmission
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What factors determine diffusion rates across membranes for non-gases?
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- concentration gradient for unionized substances
- electrochemical gradient for ions - lipid solubility - size |
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Graham's Law
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diffusion rate of a gas (or liquid) is inversely proportional to the square root of its molecular weight
BIG molecules diffused SLOWER than SMALL molecules |
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According to grahams law, what happens if you release a L of helium and O2 at the same time in a closed room?
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helium will achieve greater randomness faster
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Grahams Law
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diffusion is inversely related to the square root of its molecular weight
r = sq rt (1/mw) r = rate of diffusion |
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The transport of gases across membranes depends upon _____ and the ______ of gases involved.
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diffusion, solubility
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What law am I?
When gases are dissolved in liquids, the relative rate of diffusion of a given gas is proportional to its solubility in the liquid and inversely proportional to the square root of its molecular mass (EX: rate of CO2 diffusion is 19x higher than that of O2) |
grahams law
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What law am I?
The net diffusion of a gas across a fluid membrane is proportional to the difference in partial pressure, proportional to the area of the membrane, and inversely proportional to the thickness of the membrane. -- provides a means for calculating the exchange rates of gases across membranes ex: IAs into lungs is more efective when admin to a person w normal lung fcn than someone w diseased alveoli |
fick's law
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The total membrane surface area of the lungs (Alveoli) is about _____ and has a thickness of _____ thereby it is set up for effective gas exchange.
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100 m^2
<1 millionth of a meter thick |
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N20 is ____x more diffusable than N2, thus do not use when...
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36 x
do not use when an air filled cavity's expansion would be undesirable |
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CO2 and N20 are approx ___x more diffusable than O2.
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20 x
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The main determinant of a gases' diffusion when all other factors are equal is....
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concentration gradient
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____ increases molecular movement and therefore diffusion.
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Heat
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