plasma membranes

state the 4 steps of drug absorption

ingestion

disintegration

dissolution

absorption

what is the cell membrane majorly made up of?

phospholipid bilayer

what must a drug have to exhibit good water solubility?

several polar chemical groups, eg OH- for hydrogen bonds

describe the structure of a phospholipid

water-soluble, hydrophilic polar phosphate ‘head’ which remains on outside of membrane

hydrophobic/lipophilic fatty acid chain which remains on inside of membrane

what lipid/water solubility properties must a drug have to cross a cell membrane?

partly water-soluble - in order to penetrate the hydrophilic phosphate head

slightly lipophilic - in order to pass through the fatty acid tails

give some factors that affect the absorption of a drug into a cell

lipid/water solubility

molecular size

degree of ionisation

why are most drugs described as being poor electrolytes?

most drugs have poor solubility, and so are unable to dissociate readily

how does molecular size affect drug absorption into a cell?

affects passive diffusion across membrane (smaller = easier)

by which mode of transport do most drugs move into a cell?

passive diffusion

how does degree of ionisation affect drug absorption into a cell?

ionisation creates a chemical dipole which attracts water molecules

ionisation increases water solubility

the ionised form of a drug attracts water and so is soluble in the hydrophilic areas of the membrane

when the drug enters the fatty acid chain section, ionisation usually reverses and the drug becomes fat soluble

give some factors that affect the passive diffusion of a drug across a membrane

surface area

thickness of bilayer

concentration gradient

define passive diffusion

net movement of molecules from a region of higher concentration to a region of lower concentration

energy is NOT required

what is the cell membrane majorly made up of?

phospholipid bilayer

define active transport

the movement of molecules into or out of a cell across the cell membrane, from a region of lower concentration to a region of higher concentration using energy from ATP

uses protein carriers or channels

define endocytosis

active transport across a membrane, but not using a specific carrier, pore or channel

the cell ingests material by enveloping it in a portion of its cell membrane, then pinching off that portion of the membrane