Overview of the Mammalian Stomach
The mammalian stomach is divided into regions that are partly determined by the characteristics of its mucous membrane. The proximal end of the stomach is lined by a region of stratified squamous epithelium similar to that which lines the oesophagus (Figure 4.1); originally termed the oesophageal region but now accepted as truly part of the stomach.
The second region, the cardia, present only in mammals, is lined by a transitional region of stratified and glandular epithelium. The third compartment is the fundic region and is characterised by a lining of simple columnar epithelium containing numerous tubular glands responsible for the production of pepsin (chief cells) and hydrochloric acid (parietal cells).The fourth compartment is the pyloric region (sometimes referred to as the pyloric antrum) containing branched tubular glands producing a mucoid fluid that has little digestive activity and G cells that produce gastrin, a hormone that stimulates secretion by the chief cells and parietal cells. In some species distinct compartments are clearly recognisable in the gross specimen. This is particularly so in the domestic ruminants (see Section 4.2.2), where the region between the oesophagus and cardia consists of three compartments, the rumen, reticulum and omasum, all lined by stratified squamous epithelium. The abomasum, comprising the fundic and pyloric regions, is the equivalent of the glandular stomach of other species. This kind of stomach is known as a compound stomach; the stomachs of those species that lack gross compartments are called simple stomachs.4.2
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