RATE OF MEMBRANE MOVEMENT

A. Major Factors

TRANSPORT RATE = AREA x PERMEABILITY x NET DRIVING FORCE

B. Area (A)

1. Define: Area available for transport across cell wall or organ surface

Note: Organs whose functions include rapid transport always have a large transport surface area (e.g. lungs, capillaries, kidneys, small intestine)

C. Permeability (P)

1. Define: ease with which a particular particle passes through the membrane

example: P-Na+ = Sodium ion permeability

NOTE: For the common monovalent ions Na+, K+, and Cl-, the relative permeabilities in resting mammalian nerve and skeletal muscle cells are

P-K = P-Cl >> P-Na

D. Net Driving Force

1. Sum of passive forces (such as diffusion and electric forces) and active forces associated with living systems (more later)