Effect Of Boundary Layers On Cutaneous Gas Exchange Available to Purchase

Boundary layers may offer significant resistance to cutaneous oxygen uptake by amphibians in water. This hypothesis was tested by measuring resistance to oxygen uptake as a function of water velocity in bullfrogs submerged at 5 °C and by direct measurements of the boundary layer with oxygen microelectrodes.

The oxygen diffusion boundary layer was easily measurable with oxygen microelectrodes. The proportion of the total resistance to oxygen uptake represented by the boundary layer increased from 35 % at a water velocity of 5cms⁻¹ to over 90% at 0.1 cm s⁻¹. At water velocities below 1cms⁻¹ oxygen uptake was limited by the resistance of the boundary layer. At 0.1 cm s⁻¹, the partial pressure of oxygen immediately adjacent to the skin was only 2 kPa (15 mmHg); placing an immobilized frog ln still water was tantamount to placing lt in anoxic water. Body movements disrupted boundary layers efficiently; even occasional small movements by the animal (1min⁻¹) were sufficient to maintain oxygen uptake in still water.