Mouse brain capillaries
This false-colored scanning electron micrograph (SEM) shows capillaries or microvessels (blue/orange/purple 3D cylindrical structures) isolated from a mouse brain.
Brain microvessels are characterized by the presence of neurovascular units, the building blocks of the blood brain barrier.
The neurovascular unit is made up of endothelial cells surrounded by other cell types which regulate the exchange of molecules between the blood and the brain. This together with the thin diameter of the capillary makes it difficult for circulating drugs to reach the brain.
The diameter of each blood vessel is approximately 5 micrometers.