arterial capillary

A countercurrent exchange system is utilized between the venous and arterial capillaries.

A Metarteriole (or arterial capillary) is a short vessel that links arterioles and venules.

At this point, the free oxygen in the arterial capillaries diffuses into the swim bladder via the gas gland.

Adaptations of the peripheral include capillarization, that is an increase in the surface area that both the venous and arterial capillaries supply.

Gas is diffuses (in most cases) into the bladder through the venous capillaries, while the gases being taken away are diffused into the arterial capillaries.

Note that previously it was believed that at steady state the arterial capillaries filter fluid and the venous capillaries reabsorb it, as shown by the diagram.

The cycle of diffusion continues until the concentration of oxygen in the arterial capillaries is supersaturated (larger than the concentration of oxygen in the swim bladder).

This causes an increase in venous blood oxygen concentration, allowing the oxygen to diffuse through the capillary membrane and into the arterial capillaries, where oxygen is still sequestered to hemoglobin.