Eli5: How do bones and other organs know what shapes to grown into?

Question

Eli5: How do bones and other organs know what shapes to grown into?

In: 3675

Answer 1

How about when bones or other organs are supposed to stop growing. Let’s say a particular bone is supposed to grow until a person is 15 years old and then not get any longer. Who told the cells when 15 years was up?