Question: how do blood vessels grow?

Alison Thomson answered on 14 Nov 2014:

They grow by a process called ‘angiogenesis’, where lots of cells called ‘endothelial cells’ all get together next to an existing vessel, and attach themselves in the form of a blood vessel, and using enzymes they eat a little hole in the first blood vessel so that blood can start to flow through in to the new vessel.
The reason they know where to go is because in areas that don’t already have blood vessels there are cells that send out signals saying that they need a blood supply.

Great question – I hope I managed to answer that ok for you!