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What is Mucin is not secreted by and explain in detail?
Paneth cells are a specific type of cell within the crypts of Lieberkuhn.
These cells have atypically oriented bright eosinophilic granules containing a variety of antimicrobial proteins and play a role in mucosal immunity (and not mucin secretion)

Brunner's glands: are sub-mucosal mucus gland within the duodenum.
Goblet cells: are mucin-secreting cells.
Crypts of Lieberkuhn: are lined by goblet cells besides other cell types.

These are thus also involved in mucin secretion.