Oblige

Oblige:  1: To constrain someone or something by physical, moral or legal force or by the Exigencies of the circumstances. 

I am obliged to care for my patients while they are under my care.

2: To put someone in your debt by favor or service.

Exigent

Exigent:  Something requiring Immediate attention.  Requiring much.  Demanding

These are exigent circumstances.