I was reading an article about whey vs casein, which said casein is digested very slowly. I remember reading casein peptides in the blood stream are used by the body in a much slower way. I've a confusion between the terms digestion and blood absorption, when we say something is digested does it mean that the food is completely broken down and taken into blood or the process still continues in the blood stream.

What I want to know is protein from different sources (meat/whey/casein...) when entering the blood stream after digestion in the intestines are essentially in the same form or each one absorbed into the blood stream is in a different form which is further broken down in the blood stream.