Figure 1614

Photomicrograph of cardiac glands. This photomicrograph shows the esophagogastric junction. Note the presence of the stratified squamous epithelium of the esophagus in the upper right corner of the micrograph. The cardiac glands are tubular, somewhat tortuous, and occasionally branched. They are composed mainly of mucus-secreting cells similar in appearance to the cells of the esophageal glands. Mucous secretion reaches the lumen of the gastric pit via a short duct segment containing columnar cells. x240.

mus, the narrow segment that lies between the gastric pit and the fundic gland (Fig. 16.16). This mitotic activity provides continuous cell renewal. Most of the newly produced cells at this site become surface mucous cells. They migrate upward along the wall of the pit to the luminal surface of the stomach and are ultimately shed into the stomach lumen.

The cells of the fundic glands have a relatively long lifespan

Other cells from the isthmus migrate down into the gastric glands to give rise to the parietal cells, chief cells, mucous gland cells, and enteroendocrine cells that constitute the gland epithelium. These cells have a relatively long lifespan. The parietal cells have the longest lifespan, approximately 150 to 200 days. Although parietal cells develop from the same undifferentiated stem cells, their lifespan is distinctly different. Recently, it has been hypothesized that parietal cells may have evolved from a bacterium called Neurospora crassa that previously ex-

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