THE CAST

Three cell types around the vessel

🧱

Endothelial cells

Line the inside of the vessel and form the barrier itself

🤝

Pericytes

Wrap around the capillary, helping regulate blood flow and keeping the barrier tight

⭐

Astrocytes

Star-shaped support cells whose end-feet cover most of the vessel's outside

Together they are called the neurovascular unit.

CROSS-SECTION

Looking down a capillary

Endothelial cells form a ring around the open channel. A thin basement membrane wraps them, pericytes sit within it, and astrocyte end-feet surround the outside.

The barrier is built in layers.

THE REST OF THE TEAM

Neighbors that join in

Neurons When they become active, they signal nearby vessels to adjust blood flow

Microglia The brain's resident immune cells, which respond to injury and infection

Basement membrane A thin sheet of proteins such as collagen IV and laminin that anchors the cells

Brain activity and blood supply are linked through this unit.

CROSSTALK

The cells teach each other

📣

Signals

Astrocytes and pericytes send chemical signals that tighten endothelial junctions

🔧

Maintenance

In mice lacking pericytes, the barrier becomes leakier

🔁

Two-way

Endothelial cells signal back and help shape the cells beside them

A tight barrier is maintained by conversation, not built once and left alone.

WHY IT MATTERS FOR MODELS

Endothelium alone is not enough

Endothelial cells grown by themselves usually make a weaker barrier than the one in the body. That is why many models add astrocytes, pericytes, or both, and why the best ones try to recreate the whole neighborhood.

A good model rebuilds the neighborhood, not just the wall.

UNIT 2 STUDY COMPLETE

⭐

Ready for the Fab Challenge?

You've met the cells around a brain capillary and seen why a model needs more than one cell type.