module 1: section 3

Question 1

why is it important to know the mechanism by which a toxicant crosses a biological membrane?

Answer 1

influences the disposition of the drug within the body because absorption, distribution, and excretion all heavily depend on the ability of a chemical to cross the membranes.

Question 2

what are the 4 primary mechanisms by which chemical cross biological membranes?

Answer 2

1. passive diffusion
2. filtration
3. transporters
4. endocytosis

Question 3

describe passive diffusion

Answer 3

the movement of molecules down a concentration gradient without energy input

Question 4

describe filtration

Answer 4

movement of molecules through fenestration, or pores of specialized endothelial cells

Question 5

describe transporters

Answer 5

carrier-mediated transport through the regulated flow of molecules in/out of the cell via specialized membrane protein

Question 6

describe endocytosis

Answer 6

vesicular transport; substances and extracellular fluid moved from extracellular space into a cell

Question 7

what factors influence method of crossing membranes?

Answer 7

1. physiochemical properties: molecular weight, lipid solubility, ionization
2. cellular environment: concentration gradient of toxicant across the membrane

Question 8

describe the toxicant characteristics that affect membrane crossing

Answer 8

molecular weight: chemicals with larger MW cross biological membranes less readily than smaller
lipid solubility: more lipid soluble = more readily to cross membrane
ionization: ionized chemical less lipid soluble than their non-ionzied version

Question 9

describe the environmental factors that affect membrane crossing

Answer 9

concentration: chemicals move from an area of high concentration to low so diffuse outside of cell into the membrane.