The ultrastructure of the Goblet cell in the dog ileum at the later stage of secretion.

The globules in goblet cells in the epithelium of the dog ileum show a moderate contrast between the light and dark types. The globules appear to arise from the Golgi apparatus. Membranes encapsulate all of the globules in the earlier stages but a part of the mucosubstance undergoes a dispersion or, in some cases, possibly a fusion before their discharge into the intestinal lumen. There is little evidence of any escape of organelles into the lumen during secretion and the residual cytoplasm is always limited by a continuous membrane when the goblet is emptied. The residual portion of the cytoplasm appears to be functionally active at the stage when the goblet has been effectively emptied. Both the Golgi apparatus and the rough surfaced endoplasmic reticulum contain a substance similar to that in the light globules. The discharged mucus is distinctly different in appearance from the glycocalyx of the microvilli of nearby absorptive cells.