Pancreas of pig was encapsulated by a connective tissue capsule, which divided the parenchyma in lobes and lobules in an irregular manner (Fig 1). These findings were in accordance to the observations of
Duhan (1992) in buffalo,
Egerbacher and Böck (1997) in humans,
Dhoolappa et al. (2004) in Indian donkey,
Hamodi et al. (2013) in common gulls and guinea fowls and
Khaleel et al. (2020) in goat and
Rajathi et al. (2023) in guinea pig. The connective tissue septa had collagen (Fig 2) and reticular fibres (Fig 3) as reported earlier by
Egerbacher and Böck (1997) in humans and
Iniyah et al. (2020) in pig. These septae possessed some adipose tissue, rich blood supply, nervous innervations and a few elastic fibres, which were in consonance with the findings of
Dhoolappa et al. (2004) in Indian donkey and
Iniyah et al. (2020) in pig. The glandular parenchyma was divided into exocrine and endocrine parts (Fig 1) similar to the findings of
Duhan (1992) in buffalo,
Iniyah et al. (2020) in pig and
Khaleel et al. (2020) in goat. Exocrine part contributed roughly more than 90% while endocrine part was only 1-2% of the total glandular mass which was consistent to the observations of
Pandiri (2014) in rats and mice whereas
Khaleel et al. (2020) stated that exocrine part was 95% and endocrine part was 1-2% of the total pancreatic mass in goat. However,
Hamodi et al. (2013) observed 99% exocrine part in pancreas of common gulls and guinea fowls.
Histology of exocrine part
Exocrine part of pancreas was consisted of two components
i.e. the secretory portion known as acini (Fig 1 and 4) and the duct system (Fig 1). The pancreatic acini were of variable shape and size, surrounded by a fine network of collagen (Fig 2) and reticular fibres (Fig 3), which was in agreement to the observations of
Dhoolappa et al.(2004) in Indian donkey and
Khaleel et al. (2020) in goat. Spindle shaped, elongated and basophilic cells considered as myoepithelial cells (Fig 4) were observed on the peripheral part of acini similar to the observations of
Iniyah et al. (2020) in pig and
Khaleel et al. (2020) in goat. Acinar cells were having typical cellular detail
i.e. the basal region possessed the nucleus and the cytoplasm was basophilic in nature whereas the apical region was eosinophilic in nature containing zymogen granules, which was in concurrence with the findings of
Duhan (1992) in buffaloes,
Hamodi et al. (2013) in common gulls and guinea fowls and
Iniyah et al. (2020) pig. On the basis of difference in morphological character, size and location of nucleus and density of zymogen granules, acinar cells were classified into three types (Fig 4)
i.e. active cells, resting cells and exhausted cells. Each type of acinar cell indicated a different physiological state. Similar observations were made by
Duhan (1992) in buffaloes. The active cells had euchromatic type of nucleus which was at the basal part of the cell. The apical portion of active cells contained abundance of pink coloured zymogen granules. The resting cells had heterochromatic nucleus, which was located towards the basal portion. The heterochromatic nucleus suggested the reduced activity of the resting cells. The zymogen granules were densely packed in resting cells. The exhaustive cells were elongated in shape and possessed spherical to oval, highly euchromatic nucleus, which was located at middle part of the cell. Euchromatic nucleus suggested high cellular activity. Centroacinar cells (Fig 4) were found at the centre of acini as reported earlier by
Egerbacher and Böck (1997) in humans and
Iniyah et al. (2020) in pig. On contrary, centroacinar cells were not observed in common gulls and guinea fowls by
Hamodi et al. (2013). Intercalated ducts observed to originate from central portion of an acinus as reported earlier by
Rajathi et al. (2023) in guinea pig. The intercalated duct had flat type of epithelium, which drained its secretion into intralobulated duct. The intralobulated ducts had low cuboidal type of epithelium. The intralobulated ducts joined the small interlobular ducts, which further joined the major interlobular ducts, that had simple columnar type of epithelium (Fig 5). It was in conformity with the observations made by
Egerbacher and Böck (1997) in humans and
Dhoolappa et al. (2004) in Indian donkey. However,
Hamodi et al. (2013) stated that ductal epithelium was simple squamous to cuboidal type in common gulls and guinea fowls. These ducts contained collagen fibres along with a few reticular and scanty elastic fibres in their walls, as reported earlier by
Dhoolappa et al. (2004) in Indian donkey and
Singh et al. (2024) in pig.
Histochemistry of exocrine part
Acini exhibited PAS negative reaction for glycogen while ducts along with goblet cells displayed moderate reaction showing the presence of glycogen (Fig 6), On contrary,
Conklin (1962) reported strong PAS activity in pancreatic acini of humans while
Singh and Gupta (1999) in buffalo reported mild PAS positive reaction in exocrine part of the pancreas. Negative alcianophilic reaction was observed in the acini showing absence of weakly sulphated mucopolysaccharide. Intense alcianophilic reaction was observed in the duct along with goblet cells (Fig 7), which was consistent to the findings of
Singh and Gupta (1999) in buffalo. Earlier,
Dhoolappa et al. (2004) reported a strong positive reaction while
Hamodi et al. (2013) observed a mild positive reaction for both PAS and Alcian blue in larger ducts of exocrine part in Indian donkey and in common gulls and guinea fowls, respectively.
Iniyah et al. (2020) observed PAS positive goblet cells along with some other areas in larger ducts of exocrine pancreas of large white Yorkshire pigs. Positive PAS-AB reaction demonstrated presence of acidic mucopolysaccharide in the lumen of duct and in goblet cells along with some areas for neutral mucopolysaccharide (Fig 8). No reactions were observed for the presence of mucin. Acini displayed the presence for cysteine protein (>4%), while
Hamodi et al. (2013) reported moderate to weak reaction for proteins in common gulls and guinea fowls. Mast cells were observed randomly in whole exocrine part except for the ducts. No keratin or prekeratin was observed in whole pancreatic parenchyma.
Histology of endocrine part
It comprised the islet of Langerhans, scattered throughout the exocrine part in various shapes and sizes. The reticular fibres were predominately observed surrounding the islets. These islets had a profound blood supply exhibited by presence of numerous capillaries as reported earlier by
Duhan (1992) in buffalo and
Singh et al. (2024) in pig. These pancreatic islets comprised three major type of cell population
i.e. alpha (α), beta (β) and delta (δ) cells, in accordance to the observations of
Duhan (1992) in buffalo and
Jagapathi et al. (2012) in the cat. However,
Hamodi et al. (2013) observed only alpha and beta cells in common gulls and guinea fowls. Gomori’s stain (Fig 9) for pancreatic islets imparted purple colour to nucleus of alpha cells while, beta cell nucleus was stained dark blue with granulations in it.
Maldonado’s stain enabled to identify all the three types of cells (Fig 10). Alpha cells had round shaped, purple coloured nucleus. Majority of the alpha cell population was located at the periphery of the islet but some cells were also found towards the centre of islet of Langerhans, which was in consonance to the observation of
Kim et al. (2009) in dog and pig. Whereas,
Kim et al. (2009) in reported a different arrangement of alpha and beta cells in rodents and monkeys than that of dog and pig. Whereas,
Malik and Prakash (1972) and
Jagapathi et al. (2012) reported that alpha cells were located at the periphery of the islets in buffalo and ox and cats, respectively. Contrarily,
Khaleel et al. (2020) reported that alpha cells were located only at center of the islets in goat. Beta cells had dark blue coloured nucleus with some granular texture. The beta cells outnumbered other two cells types and were located mainly at the central part of the islet while some cells were also noticed at the periphery as reported earlier by
Mukherjee et al. (1988) and
Jagapathi et al. (2012) in sheep and cat respectively. Whereas
Khaleel et al. (2020) reported that the beta cells were only found at periphery of islets in goat. Delta cells had oval to elliptical nucleus with light blue colour having purplish tinge. Delta cells were least in number amongst all three types of cells and were mostly observed in association with alpha cells which was in concurrence with the findings of
Elayat et al. (1995) in rat. Whereas,
Jagapathi et al. (2012) reported that delta cells were found randomly in islets of cats while
Khaleel et al. (2020) observed the delta cells at periphery of islets in goat. Majority of the islets were beta cell-dominating but some alpha cell-dominating islets were also observed. Similar findings were reported by
Hamodi et al. (2013) in common gulls and guinea fowls and
Tsuchitani et al. (2016) in experimental animals.
Histochemistry of endocrine part
No activity was noticed in the islets of Langerhans with PAS and PAS-AB stains indicating absence of glycogen, acidic and neutral mucopolysaccharide, respectively. However,
Duhan (1992) in buffalo reported presence of glycogen in alpha cells while
Hamodi et al. (2013) observed PAS and alcianophilic positive reactions in islets. Weakly sulphated acidic mucopolysaccharide, strongly acidic mucopolysaccharide and mucins were not observed within the pancreatic islets depicted by negative reaction for alcian blue, colloidal iron and Mayer’s mucicarmine stains, respectively. Islets showed weak to mild reaction for presence of proteins, which was in accordance to
Hamodi et al. (2013) who observed that islet cells highlighted weak to moderate reaction for bromophenol blue. Mast cells were not observed in the islets.
