Gastric digestion of protein through pancreozyme action optimizes intestinal forms for absorption, mucin formation and villus integrity

•Intestinal proteolysis leads to free amino acids dominated by essentials with nonessential amino acids predominantly residing in the peptides.•Protein digesta enters the unstirred water layer where the amino acids are actively transported while aminopeptidases further create di- and tri-peptides for transfer.•Mucins comprising the unstirred water layer create a low pH microenvironment enabling peptides to be absorbed as either a zwitterions or nondissociated.•Dietary cystine and threonine together with glycine and proline are critical for mucin and replacement of surface cells.•Use of absorbed amino acids for maintenance of villus functioning takes priority before portal access for the body-at-large.