Digestion Tract: GIT
Stomach is the expanded part of the alimentary canal. It has the same organization as the remaining gut (mucosa, submucosa, muscularis, serosa). The inner surface has longitudinal folds called rugae, which are poorly developed in the upper stomach but more elaborate in the lower part. They disappear when the stomach is distended to accommodate expansion. Numerous openings are seen in the mucosal surface called gastric pits or foveolae>, which are easily seen in scanning electron microscopy (SEM). Gastric glands empty into the bottom of gastric pits.
Fundic Glands are composed of 4 functional cell types:
- Mucous neck cells, which are located in the neck region. They are shorter than surface mucus cells, where the nucleus tends to be spherical rather than elongate (as in surface cells). They secrete soluble mucous, compares to viscous surface mucous.
- Chief cells, which are typical protein-secreting cells that occupy the basal portion of the gland. These cells are easily identified by intense basophilia due to basal rER and apical granules. They secrete pepsin as inactive pepsinogen and a weak lipase.
- Parietal cells, also called oxyntic cells. They secrete HCl and intrinsic factor. They are larger cells and are most numerous in the upper and middle region of the gland. They appear round to triangular in shape, with the apex directed towards the lumen of the gland.
- Enteroendocrine cells, which are open (chemoreceptors) and closed types. They are located at any level of the gland and sit on the basal lamina. EM shows small, membrane-limited granules. These cells can be hard to identify.
- Undifferentiated cells, which are located in the upper neck region and give rise to the mature cells listed above.