Histology of Glandular stomach

The wall of the stomach is composed of a mucosa, submucosa, muscularis and serosa.

Tunica mucosa consists of- Surface epithelium, The glandular lamina propria, and Muscularis mucosae

Mucosa

1. Surface epithelium
   • It begins abruptly at the jagged border of stratified squamous epithelium of the oesophageal mucosa. It consists of a single layer of high columnar cells. The oval nucleus lies in the basal part of the cell.
   • No distinct striated border can be seen with light microscope. The surface epithelium is continued into depression in the gastric mucosa – the gastric pits, bottom of which show shorter and broader cells. The glands open into the bottoms of gastric pits, which correspond to ducts.
2. Lamina propria
   • Contains gastric glands supported by delicate connective tissue framework. The connective tissue contains fibroblasts and histiocytes and there is diffuse infiltration with lymphocytes. There is less connective tissue between the glands than between the pits.
   • The gastric glands are simple branched tubular glands. Several of them open into one gastric pit. These glands are of three types-
     1. Fundic glands
        • They are distributed through the greater part of gastric mucosa. Each gland consists of a body or main part, which ends below in a blind and dilated extremity (the fundus) and is continued upwards into a constricted portion, the neck, which opens into the bottom of a gastric pit. The body of the gland contains two kinds of cells- Chief and parietal.
        • Chief cells
          • These are cuboidal or pyramidal and contain coarse secretory (zymogen) granules. In H and E preparations the cytoplasm of chief cells stain blue. Nuclei are spheroid and are at the basal end, Chief cells secrete pepsin.
        • Parietal cells
          • These are larger than chief cells, and are oval or polygonal; the finely granular cytoplasm stains deeply with acid dyes (eosin). Nucleus is spherical and centrally located in the cell. These cells lie outside the Chief cells or between them. They maintain connection with the lumen by intercellular canaliculi, which extend between the chief cells. Intracellular canaliculi are also present. The parietal cells/ oxyntic cells secrete hydrochloric acid.
          • The neck of the gland is made up of mucous cells, which may be interspersed among parietal cells. They are cuboidal with oval nuclei situated at the base of the cell. The cytoplasm stains light blue in ordinary preparations. These cells secrete mucous, it is believed that the mucous secreted by these cells contains the intrinsic factor, which enhances the absorption of extrinsic factor (Vitamin B12) necessary for haemopoiesis.
        • Argentaffin cells or (Chromaffin cells)
          • These cells show fine cytoplasmic granules, staining black by silver impregnation technique may occur as isolated cells between the basement membrane and chief cells. They are said to contain, serotonin, a vasoconstrictor substance, which stimulates the contraction of plain muscle.
     2. Pyloric glands
        • These are coiled tubular glands. In sections mostly transverse and oblique sections of the tubule are seen. The ducts of the glands are longer but the body is shorter and the cells of the body resemble mucous cells.
        • The glands secrete mainly mucous. Between the cells of the gland, narrow eosinophilic Stohr’s cells are often found. The gastric pits or ducts are longer (or deeper) and are lined by eosinophilic columnar cells.
     3. Cardiac glands
        • They occur at the transition zone, between esophagus and stomach in simple stomached animals. In horse, it is restricted to the narrow zone close to the Margoplicatus junction. In ruminants, cardiac glands are located close to the omaso-abomasal junction. These are highly branched and coiled, tubular glands.
        • The ducts are very long i.e., the pits are very deep. The body has a relatively wide lumen and lined by clear pyramidal or cubodial cells with a basally located nucleus. They secrete mucous and these glands pass over gradual transition into typical gastric glands.
3. Muscularis mucosae
   • Plain muscle fibres interwoven or stratified forming a thin layer fibres extend into the lamina propria.

Submucosa

• This is made up loose connective tissue.

Tunica Serosa

• The serous coat consists of a layer of loose connective tissue which is covered by mesothelium.

Species differences

• The anterior oesophageal region of the stomach in horse is lined by a cornified stratified squamous epithelium. Behind this there is fundic gland area and then pyloric gland area. Between the oesophageal region and fundic area, there is a narrow cardiac area.
• The abomasum of ruminant consists of cardiac, fundic and posterior pyloric gland areas.
• In the carnivores there is a fundic and pyloric area. Near the cardia there is a narrow zone of cardiac gland area.
• A lamina subglandularis intervenes between muscularis mucosae and the blind ends of the glands. In old animals, it becomes stratified into an inner stratum granulosum rich in cells and an outer stratum compactum consisting of network of dense, hyaline collagenous substance.