A similar type of situation is observed in bronchial and tracheal epithelium. The name goblet cell derives from the characteristic shape of these cells in conventionally-fixed tissues: a narrow base and expanded apical portion that sometimes extends into the lumen. If special precautions are taken during fixation, goblet cells are seen as cylindrical cells.
Regardless of fixation, goblet cells have a distinctly polarized morphology. Their nucleus is at the base of the cell, along with organelles such as mitochondria, endoplasmic reticulum and Golgi. The remainder of the cell is filled with membrane-bound secretory granules filled with mucus. Secretion of mucus from goblet cells is elicited primarily by irritating stimuli rather than in response to hormones.
The lumen of the intestinal tract inevitably contains numerous irritants, and in the lung, such things as dust and smoke are potent inducers of goblet cell secretion. Secretion of mucus is by exocytosis of secretory granules. Interestingly, goblet cells have two pathways for secretion:. The mucus in goblet cell granules is condensed, but upon secretion, expands in volume tremendously and almost instantaneously picture a pressurized can of shaving foam or whipped cream.
In some systems studied, the mucin gel increases in volume fold during a period of only 20 milliseconds! A mechanism proposed for such rapid expansion of volume is as follows. Other secretory products, including lipids and "small" glycoproteins, may also be produced by goblet cells. It is possible that goblet cells have the potential to produce markedly more mucus than do the glands.
Mucins are tightly packed in the intracellular granules of the goblet cell. The morphology of these granules varies with fixation technique, and release of mucins may be via a combination of merocrine and apocrine secretion.
Discharge of mucus is accomplished remarkably rapidly tens of milliseconds and vast quantities of mucus are released size expansions from the granule of many hundredfold.
Depending upon species and preparation, goblet cells discharge mucus in response to a wide variety of stimuli, including proteinases, irritant gases, inflammatory mediators, reactive oxygen species, nerve activation and changes in the biophysical environment. Under normal conditions, goblet cell proliferation and differentiation, particularly to ciliated cells, contributes to maintenance of the airway epithelial cell population.
In addition to participating in acute airway defence, goblet cells increase in number in response to chronic airway insult, with a resultant increase in output of mucus.
The increase in number of cells is via hyperplastic and metaplastic mechanisms. Early triggers for the development of a hypersecretory epithelium include excessive discharge of mucus and increased expression of airway mucin messenger ribonucleic acid mRNA.
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