What are the functions of the parietal, chief, mucous neck, and enteroendocrine cells in gastric glands?

The source identifies parietal cells as HCl-producing cells, chief cells as secreting pepsinogen and lipases, and enteroendocrine cells as releasing chemical messengers such as histamine, serotonin, somatostatin, and gastrin. However, it does not describe a function for mucous neck cells.

In the gastric glands, parietal cells are labeled as HCl-producing cells, and the passage also states that gastrin stimulates parietal cells to release HCl. Chief cells occupy mainly the basal regions of the glands and produce pepsinogen, the inactive form of pepsin, which is activated by HCl; chief cells also secrete lipases. Enteroendocrine cells lie deep in the gastric glands and release a variety of chemical messengers into the interstitial fluid, including paracrines such as histamine and serotonin, and hormones such as somatostatin and gastrin. The source labels mucous neck cells in the figure but its text does not specify their function.