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38 Cards in this Set

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Definition of flux
Movement of solute
Net flux
Difference between greater and lesser unidirectional fluxes
Which factors increase net flux
C- concentration of solute
A - area of diffusion
Which factor when increased decreases net flux
Membrane thickness
Diffusion constant D is _
relatively ease of solute movement (permeability) in specific solutions or across cell membranes at physiological temperature
Fick diffusion constant
J net = DA (C1-C2)/x
Concentration gradient
C1-C2/x
Activity coefficient
Fraction solute dissolved
-from 0 to 1
Which compounds enter cell most readily
Hydrophobic
Which compounds enter cell least readily
Hydrophilic
Solutes that dont enter are _
reflected
Most continuous, all fenestrated capillaries are permeable to _
impermeable to _
Permeable to - small solutes (glucose), lipophilic substances
Impermeable to - colloids (albumin, globulin)
Sinusoids are permeable to _
Most of things smaller then cells
Continuous capillaries are permeable to _
impermeable to _
Permeable - lipophilic substances
Impermeable - solutes and colloids (glucose requires transport molecules)
What is a necessary requirement for osmosis
Semipermeable membrane
Energy for osmosis
Temperature
In osmotic flow water follows _
solute
What stops movement of water in osmosis
Osmotic pressure
How do you calculate osmotic pressure
P osm = n CRT
n- number of particles per mole (NaCl dissociates into 2 molecules so n=2, CaCl2 - n=3, glucose doesnt dissociate, n= 0)
T- temperature in K
R - gas constant
C- concentration of solute
Reflection coefficient corrects for _ if solute is not totally impermeable
partial permeability
Osmotic coefficient corrects for _ if salt doesnt totally dissociate
Partial dissociation
Hypotonic solutions make cells _
Swell - cells have more solute activity then solution
Isotonic solutions do what to cells?
Preserve cell size - cells and solution have equal solute activity
Hypertonic solutions make cells _
Shrink - solution has more solute activity then cell
What regulates osmolarity of extracellular fluid
Kidneys in response to ADH
Most important osmotic colloid and why
Albumin - holds negative charge of 17, when it gets trapped in the capillary it increases osmotic pressure on the walls by factor of 18
In blood vessels, what pushes fluid out and what keeps it in
Blood pressure - pushes fluid out
Osmotic pressure - keeps fluid in
Net filtration pressure is _
BP - P osm
Albumin after synthesis in liver can go where
1. Renal loss
2. Loss from capillaries
3. Protein metabolism
How does altering concentration or area affect diffusion rate
Diffusion rate is directly proportional to area and the difference in concentration, with net movement from high to low concentration
What does it mean when we say we increased or decreased the gradient for diffusion
Increased gradient implies either a greater difference in concentrations or a lesser distance for diffusion to travel. Decreased gradient has the opposite meaning.
Why does the body use both diffusion and bulk flow?
Diffusion is fairly rapid over short distances, making it unnecessary to create tubular conduits (blood vessels, airways, etc.) to every cell. However, diffusion is too slow over long distances
How do the permeability properties of cells and capillary walls differ?
Cells are impermeable to many solutes with the notable exception of lipid soluble solutes. Therefore, most solutes can exert osmotic forces on cells. Most capillaries are of the continuous or fenestrated type, which are permeable to small solutes but not to larger proteins or colloids, like albumin; proteins can exert an osmotic force across these capillaries but smaller solutes can’t. Most sinusoids have such large openings that no particles exert an osmotic force on them; capillary pressures are typically lower in organs with sinusoids and/or the organs are encapsulated. The capillaries of the blood brain barrier are more impermeable than other capillaries and react to solutes pretty much as the cell membrane does.
How would the effect of a hydrophilic narcotic on the brain differ from that of a hydrophobic narcotic
Hydrophillic substances do not cross the blood-brain barrier, so they lack CNS effects. Very young children, elderly, and persons with brain infections or injuries may respond unpredictably to hydrophilic drugs with the potential for CNS activity since these populations may lack an intact blood-brain barrier
• How does the movement of a solute with a low reflection coefficient across a cell membrane differ from that of a solute with a high reflection coefficient?
The solute with a low reflection coefficient can enter the cell more readily, so it exerts less osmotic effect on the cell than its osmolarity predicts.
If salt is being absorbed across an epithelium and capillary, what happens to water?
Water follows salts by osmosis. Osmosis provides the driving force for all water absorption. Hence, all diarrhea and all diuresis are due to non-absorption or non-reabsorption (respectively) of some solute.
Explain watery diarrhea using osmosis
All watery diarrhea is caused by either unabsorbed solutes or increased interstial pressure, much like the Starling forces across the capillary wall. The other type of diarrhea is bloody diarrhea (dysentery), which also involves some pressure forces.
These are the causes of watery diarrhea:
(1) When a person is unable to digest or absorb a carbohydrate, it becomes a solute that retains water. There are several causes of carbohydrate malabsorption, only two or three of which are common.
(2) Viruses or bacteria can inhibit absorption of NaCl or stimulate secretion of Cl-, with Na+ following as a conjugate ion.
(3) Malabsorbed fats, though they do not have much osmotic effect of their own, inhibit intestinal and colonic NaCl reabsorption. There are a plethora of causes of fat malabsorption, a few of which are common.
(4) Ingestion of non-absorbable solutes in the, such as Epsom’s salts (the proverbial ‘dose of the salts’) or excessive soluble fiber (25 g a day or so are good, much more than that can cause diarrhea).
(5) Portal hypertension and bleeding are non-osmotic causes of diarrhea.
(6) Increased motility can cause diarrhea if it causes carbohydrate or fat malabsorption; decreased motility can lead to GI infections that cause diarrhea.
• A firefigher suffers burns to her legs that cause her to lose albumin from damaged leg capillaries. Her pulmonary capillary pressure is 17 mm Hg before and after the burn, but her pulmonary colloid osmotic pressure drops from 23 mm Hg to 13 mm Hg. What will happen?
The capillary blood pressure (17 mm Hg) is pushing fluid out. This value is already high (normal is 5-7 mm Hg) so there was a pre-existing condition. The colloid osmotic (or oncotic) pressure is the main force preventing fluid from moving out. When the capillary blood pressure exceeds the oncotic pressure there is net filtration of fluid out of the pulmonary capillaries, into the lungs. This will cause pulmonary edema.