The gastric glands, on the basis of their distribution in the stomach, can be classified under following heads:
Image Source: pnas.org
1. Cardiac glands:
These glands are found scattered in the cardiac part of the stomach. They are single or tubulo-racemose glands lined by small columnar granular cells.
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These glands probably secrete mucus, a substance which makes the food soft and slipery for onward movement in the system.
2. Fundal glands:
These glands are compound tubular glands lined with columnar epithelium. The cells are polyhedral, coarsely granular and are called central or Chief cells.
There are another group of spherical cells between the basement membrane and the layers of the central cells, these are known as parietal or oxyntic cells which secrete hydrochloric acid to make the appropriate medium for the gastric enzymes.
3. Pyloric glands:
These are compound convoluted tubulo- alveolar glands of which the ducts are lined with columnar cells and the tubules by finely granular cubical cells.
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The gastric glands open by single mouth at the bottom of tiny pits, gastric foveola. Sometimes a single foveolns receives secretions of two or more glands, and are throughout scattered over the gastric mucosa, the lining epithelium is columnar and continuous on both the surface as also in the foveola and gland tubules.
The central cells and pyloric gland cells secrete an enzyme called pepsin. The milk curdling enzyme is also secreted by these cells which is commonly known as rennin. But according to Lim the pyloric gland cells secrete a viscid alkaline juice without any pepsin.