Light and electron microscope studies on the nasopharynx and nasopharyngeal tonsil of the horse.

The research article describes a detailed microscopic study of the nasopharynx and nasopharyngeal tonsil in young horses. Using both light and electron microscopes, it provides a comprehensive analysis of the cell structure and distribution in these areas.

Microscopic studies and findings

• The study involved light and electron microscope evaluation of the nasopharynx and the nasopharyngeal tonsil of 15 young horses to understand their cellular composition.
• The study found that these areas are lined with pseudostratified columnar ciliated epithelium and goblet cells. Pseudostratified columnar epithelium is a type of tissue composed of a single layer of cells that, due to the varying lengths of the cells, appears to have multiple layers. These cells also have cilia, small hair-like structures used to move mucus and other substances.
• Goblet cells are specialized cells found in the epithelial layer and their job is to secrete mucus in order to protect and lubricate the mucous membranes.

Lymphoid Tissue Characterization

• The lymphoepithelium of the nasopharyngeal tonsil was observed to be folded, forming crypts. These crypts were lined with follicle-associated epithelium, which differed in structure from the general epithelium. Specifically, it was composed of stratified cuboidal epithelium, did not feature cilia or goblet cells, and exhibited infiltration of lymphocytes, a type of white blood cell involved in immune responses.
• The lamina propria mucosae of the nasopharyngeal tonsil, the soft layer of tissue underneath the epithelium, contained well-developed lymphoid tissue and clusters of seromucus acini, which are clusters of cells responsible for producing serous and mucus secretions.

Electron Microscope Findings

• Scanning electron-microscopy illuminated a dense mat of cilia covering the nasopharynx and nasopharyngeal tonsil, suggesting their protective role for these structures in horses.
• The follicle-associated epithelium was observed to be comprised of varying populations of microvillus cells, M cells with very short microvilli, as well as a few squamous and intermediate cells.
• Upon closer examination, the microvillus cells located deeper within the follicle-associated epithelium were found to have larger microvilli and a cytoplasm rich with organelles such as mitochondria, smooth and rough endoplasmic reticulum, Golgi complexes, and lysosomes, all of which are involved in various cell functions.
• The M cells observed had a flatter surface, more electron-dense cytoplasm, and contained small vacuoles situated above the nucleus, in addition to the organelles seen in microvillus cells. These cellular features suggest possibly different functions and properties of M cells in relation to microvillus cells in this region.