The Harderian gland of
Pati duck was covered by a capsule consisted of connective tissue, blood vessels, nerves and lymphatices (Fig 1 and 2). The similar finding was reported by
Brobby (1972) in duck,
Liman and Gülmez (1996) in domestic geese and
Mobini, (2012) in native chicken. The thickness of the capsule of the Harderian gland increased slightly along the advancement of the age. The capsular connective tissue penetrated the parenchyma of the Harderian gland in the form of septa (Fig 2). The thickness of the septal connective tissue also increased from 0 weeks to 42 weeks age group. The average thickness of the capsule of the Harderian gland of
Pati duck is shown in the Table 1. Similar finding were observed by
Mobini, (2012) in native chicken;
Kleckowska-nawrot, et al. (2015) in Ostrich;
Ali et al., 2016 in pigeon and
Bejdic et al., 2018 in laying hens. In the capsule a noticeable amount of connective tissue and nerve fibers were present in all the age group of duck. The amount of collagen fibers present in the capsule and as well as in the septa were increased from 0 weeks to 42 weeks age group
i.
e. distribution of the fibers became more prominent along the advancement of the age (Fig 3). The distribution of the fibers gradually decreased from capsule to septa towards the centre of the gland. The reticular fibers were observed very prominent in inter lobar, inter lobular and in between tubules rather than the capsule. The reticular fibers were very fine, form the net work along the tubular core beneath the epithelium (Fig 4). The elastic fibers were found along with the capsule, septa in an increasing trend along with the advancement of age (Fig 5). The nerve fibers of the Harderian gland were noticed in the capsular, inter lobar and inter lobular connective tissue and extended up to the base of the lining epithelium (Fig 6). The present findings were in accordance with the findings of
Brobby (1972) in the Harderian gland of domestic duck,
Mobini, (2012) in domestic chicken;
Kleckowska-nawrot, et al. (2015) in the Harderian gland of Ostrich.
The Harderian gland of the
Pati duck was compound tubular gland.
Payne (1994) and
Chieffi et al., (1996) also reported that the Harderian gland was usually compound tubulo-alveolar type, but sometimes it might also be compound tubular in avian species. From the capsular connective tissue of the periphery, the primary tubules were radiating towards the inner side of the gland and then the secondary tubules emerged from the primary tubules and then the tertiary tubules (Fig 7). The tertiary tubules were ended at an apical ending or sometimes it was connected to other tertiary tubules and look like a network of tubules inside the lobules. The tertiary tubules which were at the middle or centre of the gland they had the free apical end piece and which indicated the future expansion of the gland (Fig 7).
The columnar epithelium cells lined the tubules. The present findings were in agreement with the finding of
Brobby (1972) in domestic duck. The tubules were irregular in shape and size and there were wide lumen within the tubules. These tubules were distributed with in a lobule and such several lobules together formed the lobe and then the gland. There was a central cannel in each lobule. There was no cortex and medulla in the gland, the tubular structures were uniformly distributed within the lobule. The central cannel ultimately converged to the main duct of the gland. The Harderian gland was composed of many lobules arranged around a central cannel and each lobule contained a central lumen and corpus or body reported by
Boydak and Aydin (2009) in domestic geese,
Kozlu et al., (2010) in the osprey,
Dimitrov, (2012) in guinea fowl and
Indu et al., (2014) in the Harderian gland of White Pekin duck.
The primary tubules divided to several secondary tubules after a short distance from the periphery. The secondary tubules and the tertiary tubules were connected to other such tubules. It was difficult to recognize and differentiate the Primary, Secondary and Tertiary tubules. The average thickness of the capsule, diameter of the Primary, Secondary, Tertiary tubules and the height of the tubular secretary epithelium were recorded and shown in the Table 1. Similar results were reported by
Dimitrov, (2012) in the Harderian gland in helmeted guinea fowl. In the present study, the capsular thickness and the diameter of the tubules showed a uniform increased trend along with the advancement of the age. The height of the tubular epithelium increased slightly, remained almost same in all the age group.
The lining epithelium was simple columnar and the oval or round nucleus was present near the basement membrane. The nucleus of the secretory cell was darkly stained in routine H&E staining. The cytoplasm of the cells occupied by mucous secretion of the cell so during the routine staining procedure the apical portion of the cells gave an appearance of an empty space (Fig 8). Some of the secretory cell projected in the central canal took stain homogenously. The finding of the present study was supported by the findings of
Brobby (1972) in domestic duck,
Kleckowska-nawrot, et al. (2015) in the Harderian gland of Ostrich;
Ahmed et al., (2016) in chameleons and
Bejdić et al., (2018) in the Harderian gland of laying hen.
In the inter tubular connective tissue the lymphocyte, plasma cells were present and population of these cells were increased towards the central canal and their’s numbers accelerated by the advancement of age (Fig 9, 10). These inter tubular connective tissue (core) converged to form inter lobular connective tissue and looked like a network. A triangular like area was formed by merging of inter lobular connective tissue where the lymphocyte, plasma cell and myoepithelial cells were more densely populated.
Altunay and Kozlu (2004) and
Ali et al., (2016) reported the presence of myoepithelial cells with darkly stained flat nucleus surrounding the secretary cells in the Harderian gland of Ostrich and Chameleons respectively. In the present investigation it was observed that the aggregation of the lymphocytes in inter tubular space showed an increasing trend from 0 weeks to 42 weeks age group. This was due to the gradual exposure to the antigens present in the environment with advancement of age of the birds.
Bejdic et al., (2014) also reported an increased trend of the lymphocyte and plasma cell in the Harderian gland of laying hens.
The duct of the Harderian gland of
Pati duck was hollow tubular organ and consisted of the typical histological layers.
The lining epithelium was columnar varying in height. The nucleus was round or oval and placed towards the basal border. The cytoplasm was homogenous and in some cells vacuole was observed at the apical border. The lamina propria consisted of areolar connective tissue with aggregated lymphocytes. The lamina muscularis mucosae was interrupted as some lymphatic nodules passed from the lamina propriya to submucosa (Fig 11). The blood vessels, nerve fibers, connective tissue fibers and lymphatics were observed in sub mucosa as well as in the lamina propria.
Burns and Maxwell. (1979) reported the duct of the Harderian of the turkey, fowl and Duck lined by single layer of epithelium and the cells varied from cuboidal to columnar.
Kleckowska-nawrot, et al. (2015) described about the Harderian gland of Ostrich (
Struthio camelus domesticus) that the primary ducts were lined by a single layer of high columnar epithelial cells with spherical or oval nuclei concentrated near the base of the cell and the secondary ducts were lined by cuboidal cells.
Boydak and Aydin. (2009) also reported in the Harderian Gland of domestic geese that nuclei of myoepithelial cells were present at the base of the ductal epithelium. In the present the study, it was observed that the tunica muscularis of the duct of the Harderian gland consisted of smooth muscles, inner circular and outer longitudinal thin layers (Fig 12). The tunica serosa was blended with the surrounding orbital fascia. There were few lymphatic nodule very distinctly present extended from the lamina propria to tunica musculosa. The lymphocytes were very densely packed with in the nodule and germinal centre was not observed so far.
Burns and Maxwell, (1979) observed the similar findings in the duct of the Harderian of the turkey, fowl and Duck.
Mobini, (2012) reported in native Chicken that there were crypts along the duct and solitary lymphoid nodules were present near the crypts but the germinal centres were not evident.
