For the simplified case of transport through skin, assume total diffusional resistance of skin is entirely due to the stratum corneum and none through the sweat ducts, etc. Consider application of some medication to the surface of skin, maintaining a concentration of 10 , glee of the medication at the skin surface. The inner surface of the stratum corneum is assumed to be maintained at essentially zero concentration since the molecules are removed as soon as they reach the rnicrocirculation by a sufficiently high peripheral blood flow through skin. The thickness of the stratum corneum is 1 micron (10^-6 m). The diffusivity through the stratum corneum for the medication (a low-molecular-weight non-electrolyte) is 10^ -10 cm^2/s.

(a) Prior to achieving steady state, if the initial concentration of the medication in the skin is zero, estimate the time required before an appreciable amount of the medication diffused to the other side of the stratum corneum.

(b) Calculate the concentration of the medication at a depth of 0.1 microns in the stratum corneum at that time.

(c) Calculate the flux of medication into the stratum corneum surface at that moment in time.