Marching One By One

What am I looking at?

This is video shows several different views of blood flowing through the vessels in the tail of a freshwater fish. These vessels are so small that the blood cells need to line up to move through the vessels.

Biology in the background

The circulatory system in fish serves the same purpose as it does in humans – to bring oxygen and nutrients to cells throughout the body. Blood vessels vary in size considerably. The blood vessels around the heart and gills of a fish can be quite large. The heart pumps blood to the gills, where it’s oxygenated, and then on to tiny blood vessels called capillaries at the tips of the appendages, such as the fins and tail.

The walls of these tiny vessels are very thin, allowing oxygen to pass by diffusion from the red blood cells to the cells in the surrounding tissue. In fact, capillaries are organized so that no cell is more than 100 micrometers (slightly more than the width of a human hair) from a capillary. This means that all cells are close enough to absorb nutrients via diffusion from the capillaries.

The blood cells passing through these veins are about 8 micrometers wide, or roughly 10 times smaller than the width of a human hair.

Technique

This image was created using differential interference contrast, a type of light microscopy.