Histomorphology and scanning electron microscopy of the pharyngeal tonsil in goats

Abstract

Gross and histological studies were conducted on the pharyngeal tonsil of six male crossbred goats of six months of age. In the nasopharynx, pharyngeal tonsil was located on the caudal part of the pharyngeal septum and was 5.54±1.41cm long and 2.19±0.92cm wide. It presented numerous longitudinally arranged primary and secondary folds. Histologically the tonsil was lined by pseudostratified ciliated columnar epithelium comprising of 8-14 rows of nuclei of three types of cells, viz. basal, supporting and goblet cells. This epithelium was transformed at places into follicle-associated epithelium (FAE) and was characterized by decreased height of the epithelial cells, absence of cilia and goblet cells and heavy infiltration of lymphocytes through the interrupted basement membrane. The height of surface epithelium was 87.33± 1.20μm and that of follicle-associated epithelium was 52.33± 5.21μm. Propria-submucosa comprised of a central axis of loosely arranged connective tissue with dense aggregates of lymphoid tissue, fine blood capillaries and few nerve fibres folded around it. The cryptolymphatic units and tonsillar nodules of varying shape and dimensions constituted the majority of the lymphoid tissue. The average diameter of lymphoid nodules was 921.67±8.72μm and the lymphocyte count per nodule was 32233.23±324.24. The average number of lymphatic nodules counted per field under low power magnification of microscope was 2.5±0.43 and the internodular distance was 29.83±1.40μm. In scanning electron microscopy surface of the pharyngeal tonsil was covered by two types of epithelium viz., the ciliated respiratory surface epithelium and the FAE consisting predominantly of three types of non-ciliated microvillus cells.