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Fig. 1. Normal developmental pathways in the gastric unit of the adult
stomach. (A) The epithelium of the corpus (body) consists of
repeating, invaginating units that can be further subdivided into four zones:
the pit, composed of mucus-secreting pit cells; the isthmus, where the
multipotent stem cell resides; the neck where the mucous neck cells and the
vast majority of the acid-secreting parietal cells reside; and the base,
filled with digestive-enzyme-secreting zymogenic cells. (B) Key
differentiation pathways in the gastric unit are depicted, with the gastric
lumen to the left. The parietal cell arises within the isthmus. Pit and neck
or zymogenic cells develop along well-defined, spatiotemporally organized
developmental gradients. Neck cells are thought to enter the base and then
become ZCs. (C) The neck and base of a single unit are depicted (unit
delimited by white dashed line) in this Toluidine Blue-stained, 1 µm
plastic-embedded section, oriented as in the cartoon in B. Inset: shaded
rectangle in the neck zone of the photomicrograph at left with the gastric
unit lumen outlined in gray. (D) TEM showing a typical neck cell (left)
and a typical basal (i.e. mature) zymogenic cell (right). Inset: cytoplasmic
projection of neck cell stretching between adjacent parietal cells (one
labeled PC); note the nascent network of rER (arrow), which must become the
extensive lamellar network in the mature zymogenic cell.
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