Chapter 5 (page 21)

The Pyloric Sphincteric Cylinder in Health and Disease

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Chapter 5 (page 21)

Oxyntic Zone

This zone comprises the greater part of the fornix and corpus, i.e. the proximal two-thirds or more of the stomach. The glands are variously known as fundic glands, proper gastric glands or principal gastric glands. As one of their most important properties is the secretion of gastric acid, Grossman (l958) suggested the term "oxyntic" (Greek: acid- forming) as an appropriate indicator of this glandular zone. The mucosa here is much deeper than in the cardiac zone and contains a greater number of glands. The pits are shallow and the glands extending from the bottoms of the pits are 2 to 3 times as long as the pits are deep.

Each principal gastric gland is composed of 4 kinds of cells (Bevelander and Ramaley l979):

Chief, zymogenic or peptic cells. These are situated mostly in the deeper parts of the glands. They exhibit secretory granules containing the precursors of pepsin.
Parietal or oxyntic cells. These are most numerous in the necks of the glands. They do not border directly on the lumen, but are crowded away from it by peptic cells. Each cell is roughly triangular in shape, with the apex projecting towards the lumen between the sides of two peptic cells that border it. These cells are intensely acidophilic, contain the gastric proton pump mechanism, and produce the antecedent of hydrochloric acid; they are also believed to elaborate intrinsic factor. The secretion of oxyntic cells must pass between adjacent peptic cells that almost cover them, to reach the lumen.
Neck mucous cells. These cells resemble the mucous cells of the cardiac and pyloric zones. They are relatively few in number and are lodged between the parietal cells in the necks of the glands; they are smaller than the surface mucous cells and their mucigen granules are larger and less dense than those of the surface cells (Bevelander and Ramaley l979). The secreted mucus is somewhat different from that secreted by the surface mucous cells (Leeson l976).
Neuroendocrine or APUD cells. These small, granulated cells occur singly in the epithelium of the gastric mucosa (Bloom and Fawcett l975). They are scattered between the peptic cells and are few in number. It is accepted that some of these cells are the site of synthesis and storage of serotonin (5-hydroxytryptamine). Cells of the APUD line are much more numerous in the pyloric mucosal zone and will be described separately (Chap. 9).

The glands of the oxyntic zone produce nearly all the enzymes and hydrochloric acid secreted in the stomach; they also produce some of the mucus.

Pyloric Zone

This zone comprises roughly the distal third of the stomach. Normally it extends further along the lesser curvature than the greater, but its boundaries may vary (vide infra). The pits are deeper in this zone than elsewhere in the stomach, extending into the mucous membrane for half its thickness. The glands are also of a simple, branched tubular type, but they branch more extensively and the tubules are coiled.

The glands contain the following types of cells:

Mucous cells resembling the neck mucous cells of the oxyntic glands. These large, mucus-secreting cells constitute the overwhelming number of cells in the pyloric glands. They have a pale cytoplasm containing indistinct granules, the nucleus is often flattened against the base of a cell, and short microvilli covered by a layer of mucus, are present on the luminal surface.
Parietal cells. A few isolated parietal cells may be present among the mucous cells (Ito l967). Parietal cells also occur in the transitional region between the pyloric and oxyntic zones (Bevelander and Ramaley l979).
Neuroendocrine or APUD cells. These cells are much more numerous in the pyloric than in the cardiac and oxyntic zones; when compared with the mucous cells they are still relatively few in number. With light microscopy they have been called enterochromaffin cells. With electron microscopy their cytoplasmic granules are clearly visible after staining with chromium or silver salts. On the basis of their staining reactions, the cells have been divided into two types, viz. argentaffin cells, in which the granules reduce silver without pretreatment, and argyrophilic cells, in which a reducing substance is required before the granules will react with silver (Bloom and Fawcett l975) (Chap. 9).

The glands of the pyloric mucosal zone do not produce enzymes, but secrete mucus; this zone is also an important producer of endocrine, paracrine or neurocrine regulatory peptides by virtue of the APUD cells contained in its glands (Chap 9).

Anatomical Extent and Boundaries of the Pyloric Mucosal Zone

The various mucosal zones of the stomach are not sharply delimited, and along the borderlines the glands of one region mingle with those of the adjoining region; intermediate glands may be present between the pyloric and body (i.e. oxyntic) mucosal zones (Bloom and Fawcett l975).

The extent of the pyloric mucosal zone, and its boundaries on the oral and aboral sides, may be determined by microscopic, macroscopic, surgical and other methods. The microscopic identification of the pyloric mucosa in morbid anatomical specimens is probably the most accurate method of determining the boundaries of this zone. For instance, it has been stated in histology that the pyloric mucosal zone usually comprises the distal 4-5cm of the stomach, and that it extends farther along the lesser curvature than the greater (Bloom and Fawcett 1975).