Scheme of the eutherian gastrointestinal system, showing gastric glands and specific cell types. Proteins secreted by each cell type and directly implicated in food digestion are indicated, highlighting in red those proteins that are absent in platypus. *Gastric intrinsic factor is produced by parietal cells in humans but in the pancreas of monotremes and other mammals.
Ordoñez et al. Genome Biology 2008 9:R81 doi:10.1186/gb-2008-9-5-r81