lecture 18

Question 1

Name the factors that determine drug absorption across a membrane

Answer 1

characteristics of the membrane
mechanisms of passage across membrane
dwell time of drug-membrane interface
physiochemical characteristics of the drug
pH of the microenvironment
surface area of absorptive surface

Question 2

Identify the site in the GI tract where most drug absorption occurs

Answer 2

small intestine- the convoluted folds of the small intestine greatly increase the surface area for drug absorption

Question 3

Describe the mechanisms by which drugs cross biological membranes

Answer 3

facilitated diffusion- with concentration gradient
active transport, no energy requirement
transcellular diffusion- against concentration gradient using ATP
paracellular diffusion-
efflux transporters
endocytosis

Question 4

Differentiate the two forms of carrier-mediated absorption, facilitated diffusion and active transport

Answer 4

facilitated diffusion- goes with the concentration gradient only; molecules can bind to special protein carriers in the plasma membranes; protein carrier facilitates the diffusion process and does not require energy; molecule is released on the other side of the membrane; protein carriers transport only certain molecules across the membrane down their concentration gradient
active transport- may go against the concentration gradient; integral protein binds the ion and uses ATP to move the ion to the other side of the membrane

Question 5

Describe the impact of efflux transporters on drug absorption from the small intestine

Answer 5

limited drug absorption
enhanced drug elimination
limited distribution

Question 6

Identify the mechanism by which nanoparticles cross biological membranes

Answer 6

endocytosis