Exam 2 Diffusion Flashcards
A type of diffusion that is considered “free” (uncombined/combined)
Uncombined
A type of diffusion with extracellular or cellular constituents (uncombined/combined)
Combined
T or F: Diffusion occurs in a purely random fashion if the molecules are not charged and moving in an electrical gradient
True
Transfer of most drugs across a biological membrane occurs by ______ diffusion from a region of higher activity to a region of lower activity
Passive diffusion
Fick’s Law equation
(dM/dt) = (DA(c1 - c2)) / x
dM/dt = rate of diffusion A = area of membrane D = diffusion coefficient c1 = concentration of donor side c2 = concentration of receptor side x = membrane thickness
Permeability constant equation
P = D/x, cm/sec
Unlike synthetic membranes, biological membranes are ____ (uniform/patchy)
Patchy
P, D, and x are (absolute/mean) values of the whole membrane?
Mean values
With time, c1 approaches c2 in a(n) (linear/exponential) mode
exponential (first order) mode
When is equilibrium established in the concentration gradient?
When c1 = c2
In almost all cases of oral drug administration, the (blood/GI) compartment functions as a “sink”
Blood
Diffusion of (charged/uncharged) molecules is known as nonionic diffusion
Uncharged
What does Brownian Motion measure?
Distance traveled by the molecule
What type of particle is the Stokes-Einstein equation used for?
Spherical particles
What is the radius in angstroms of sucrose?
4.4 A
What is the radius in angstroms of albumin?
35 A
What two factors determine the probability of an ionized drug penetrating a membrane?
- Concentration (chemical) gradient
2. Potential difference (electrical gradient) across the membrane
A biological membrane has which charge on the intracellular portion?
Negative
A biological membrane has which charge on the outside?
Positive
A cationic drug molecule is repelled by the positive charge on the outside of the membrane. Only molecules with (low/high) kinetic energy pass through the barrier
High kinetic energy
Once a cation is inside the membrane, it is attracted by the (positive/negative) charged intracellular surface, and repelled by the (positive/negative) outer surface
negative; positive
Since there is also a _____ difference across the membrane, the cation is also moving “downhill”
concentration difference
“downhill” means moving from higher to lower concentration
If a molecule is moving downhill, then it is moving (with/against) the electrochemical gradient?
with the electrochemical gradient
Why might a polyvalent cation never penetrate the membrane?
It will be greatly repelled by the outside of the membrane
The type of movement of a substance through a biological membrane at rates much greater than would be anticipated based on the polarity of the solute and its molecular size
Facilitated diffusion
In facilitated diffusion, particles move (uphill/downhill)
Downhill
Facilitated diffusion relies on what type of molecule?
Carrier molecules
T or F: Facilitated diffusion uses a drug-carrier complex that has a lower permeability than the drug alone
False: the drug-carrier complex has a greater permeability than the drug alone
What can happen to the carrier complex after it crosses through the membrane?
The carrier is returned to the original side of the membrane to be reused or to be constantly produced and eliminated
Transport of a substance through a biological membrane uphill against its electrochemical gradient; energy dependent
Active transport
What type of transport involves the movement of some drugs across neuronal membranes?
Active transport bitches
Pinocytosis is a type of ______ that is energy (independent/dependent) relatively (fast/slow) and (efficient/inefficient)
phagocytosis; energy dependent; slow; inefficient
The creation of a pouch into a saccular structure in which extracellular material is trapped
Invagination
Anti-inflammatory agents that significantly inhibit pinocytosis in macrophages and other cells involved in inflammation
Adrenal gluccocorticoids
What is the diffusion route that involves dissolution in the membrane lipids, followed by diffusion to the far side of the membrane into the cytosol
Partitioning
The presence of macromolecules (proteins) in the cytoplasm results in a colloidal preparation known as
Sol
When traveling through pores, the ____ of the molecule must be smaller than the pore
Diameter
How do water-soluble, lipid insoluble molecules pass through the membrane?
Pores…. rarely pinocytosis
T or F: A drug with a low lipid solubility in the presence of a membrane carrier or active transport system can still penetrate through the membrane
True
What is the major barrier for drugs with low lipid solubility when trying to pass through the membrane?
The interaction between the polar solute and water - it is difficult for the solute to leave water and enter the lipid
T or F: Drugs with a high lipid solubility do not pass easily through the membrane
False; drugs with a high lipid solubility pass easily through the membrane
The _____/_____ partition coefficient is more important than lipid solubility itself when determine which molecules will pass through the membrane
lipid/water partition coefficient
T or F: A favorable partition coefficient sufficient for absorption to occur
False; there must be a significant concentration of the drug in water or extracellular fluid as well
What two factors determine the partition coefficient of a drug?
- Polarity
2. Size of the molecule
Drugs with a (high/low) dipole moment have low lipid solubility
High
A highly dipolar molecule with a low partition coefficient that does not penetrate into cells
Sulfisoxazole
A less dipolar molecule that has a chloroform-water partition coefficient 10 times that of sulfizoxazole and readily penetrates cells
Sulfadiazine
Ions of (large/small) diameter penetrate membranes
small diameter
T or F: For weak acids and bases, the unionized form, with a favorable partition coefficient, penetrates biological membranes at a much faster rate than the ionized form
True
As ionization increases, lipid solubility (increases/decreases) and passage through charged membranes (increases/decreases)
decreases; decreases
For all practical purposes, only the (ionized/unionized) form is said to pass through the membrane
Unionized form
Which molecules use passive diffusion to move through the membrane?
O2, CO2, fatty acids
Which molecule uses facilitated diffusion to pass through the membrane?
Vitamin b12
Which molecules use active transport to pass through the membrane?
Sugars, L-amino acids, sodium, potassium, chloride
