Fig. 3. Three steps in the modeling process applied to the secretory canaliculi of a parietal cell. (A) A single thin section from a series of 30 consecutive serial sections from a specific intracellular region. In this section two canaliculi are outlined (blue) to form one set of contours defining the canalicular surface (exclusive of microvilli, which project into the lumens of the canaliculi). Bar marker is 1 µm. (B) A series of consecutive canalicular contours traced from 29 serial sections as shown in (A) (one contour was not included in the data set owing to a fold in the section). (C) Meshed model of three canaliculi from contours shown in (A) and (B). Interconnections can be seen between two of the canaliculi in some planes. Morphological complexity made it difficult to follow the exact outline of the entire canalicular surface including each microvillar extension, so this model was constructed using only the surface that outlined the canaliculus at the base of the microvilli.