What is the difference between Alimentary and Elementary?

What is the difference between Alimentary and Elementary? : 
Alimentary : 

( 1 ) Of food and digestion

What is an alimentary canal? 

My father has an alimentary problem. 
Elementary : 

( 1 ) Simple, not developed, in the beginning stage

You should fully comply with the elementary rules of social conduct. 

Please, first of all address our elementary issues.