bio

Gill lamella

The thin, blood-filled plates arrayed along a fish gill, where the actual gas exchange happens. Water flows over them and oxygen diffuses into the blood inside. To wring the most oxygen from a medium as oxygen-poor as water, the lamellae push surface area to the maximum and run the blood opposite to the water - the countercurrent trick. They are life's answer to Fick's law in the hardest environment of all: underwater.