Whether the peptides are absorbed by the mucosa and what the mucosa releases into the blood is still a question. The mucosa cleaves the peptides further into single amino acids and releases them into the blood stream. But if this was always true, all proteins would appear as free amino acids. This would not explain the different metabolic, physiologic and pharmaceutical response of our body to different proteins and peptides. It is more likely that some smaller peptides are entering the blood stream as such and then causing different metabolic reactions.