Gross morphological studies
The pancreas of Large White Yorkshire pig was a lobulated gland with irregular margins and was located along the dorsal aspect of the abdominal cavity behind the stomach left to the median plane. This was similar to the observation made by
Iniyah et al. (2019). The pancreas was pale pink in colour in fresh state and it is covered by a large amount of fat similar to the reports of
Iniyah et al. (2019) in pig, in Indian donkey it was greyish pink to pale brown
(Dhoolappa et al., 2004) and in camel greyish pink in colour (
Ali and Masaad, 2007). It appeared as triangular shape organ, consisted of three lobes
viz., splenic, duodenal and connecting lobe. The triangular shape and lobulations was similarly observed in pig by
Iniyah et al. (2019), in horse, Indian donkey and sheep
(Dhoolappa et al., 2004) and shape of caudally opened ‘V’ in dog
(Tsuchitani et al., 2016). Between the splenic and connecting lobes is a “bridge” of pancreatic tissue serving as an anatomical connection between the two lobes. The pancreas of Large White Yorkshire pig has only one pancreatic duct that opened from the duodenal lobe similar to the report of
Nickel et al. (1973) in pig (Fig 1).
The average weight of the pancreas in the adult Large White Yorkshire pig was 90.91±0.32 g. However, the average weight of donkey pancreas was 171 g (
Ali and Masaad, 2007) and 95 g in Indian donkey
(Dhoolappa et al., 2004). The changes in the weight of pancreas may be due to variation in age and species difference. Among the three lobes, it was observed that the splenic lobe is the longest and widest, the duodenal lobe was long but thinnest and the connecting lobe was the shortest and thickest (Table 1). This was
similar to the observation made by
Iniyah et al. (2019) in pig.
Histological and histochemical studies
The pancreas of Large White Yorkshire pig was an encapsulated, lobulated compound tubuloacinar gland consisted of both exocrine and endocrine parts. It is covered by a connective tissue capsule made up of collagen fibres predominantly, but reticular and elastic fibres were sparse in the capsule. These observations were similar to report of
Dhoolappa et al. (2004) in the Indian donkey,
Garg et al. (2007) in porcupine,
Kalita et al. (2019) in Zovawk pig and
Rajathi et al. (2023) in guinea pig.
The septa from the connective tissue capsule extended into the parenchyma and divided into complete and incomplete lobules (Fig 2A). Each lobule consisted of secretory units and intralobular ducts in exocrine part and islets of Langerhans in the endocrine part. The septa contained collagen fibers in the interlobular locations especially around the ducts and blood vessels (Fig 2B). Furthermore, fine networks of collagen fibres were noted between the acini and islets of Langerhans. These observations were in accordance with the findings of
Dhoolappa et al. (2004) in the Indian donkey,
Morini et al. (2006) in rat and
Kalita et al. (2019) in Zovawk pig. The secretory units were tubuloacinar with prominent acinar portion. These were similar to the report of
Kalita et al. (2019) in Zovawk pig: Tubuloacinar but showed dominance of the tubular portion
Stinson and Calhoun (1981) in ruminants. However, the secretory units of the donkey and that of the horse are tubulo-alveolar (
Sisson and Grossman, 1964). The acinar cells were pyramidal in shape, have spherical or oval nuclei resting upon a basal lamina and were surrounded by delicate reticular fibers. Similar observation was reported by
Kalita et al. (2019) in Zovawk pig. Two types of acinar cells were identified on the basis of shape, location of the nucleus and its chromatin content
i.e. active acinar cell and resting acinar cells (Fig 2C). The nucleus of the active acinar cells were spherical in shape, located at the center and are euchromatic whereas the nucleus of resting acinar cells were also spherical in shape, heterochromatic and placed very close to the base of the cell. The amount of zymogen granules was more as compared to active acinar cells. Similar observation was report by
Kalita et al. (2019) in Zovawk pig. In addition to the above, there is presence of exhausted cells, in which the nucleus was spherical and located almost in the center of the cell in human (
Bloom and Fawcett, 1968), in camel and donkey
(Mukherjee et al., 1986).
The duct system of the pancreas consisted of large interlobular, medium intralobluar and small intercalated ducts (Fig 2D). The mucosa of the small intercalated ducts was lined by flattened cuboidal type of epithelium. The cells from the ductal epithelium extended into the lumen of the acinus as centroacinar cells of pancreas. These cells can be clearly demarcated from the acinar cells, as these cells were smaller than the acinar cells and had few granules in the cytoplasm. This is similar to the observation reported in buffalo (
Davinder and Gupta, 1999) and in Zovawk pig
(Kalita et al., 2019). The large intralobular duct was lined by single layered cuboidal epithelium. These ducts consisted of distinct basal lamina and were surrounded by collagen, reticular and few elastic fibres around the ducts (Fig 2E and 2F). The intralobular ducts were present within the lobules. This is similar to human pancreas (
Bloom and Fawcett, 1968) and in Zovawk pig
(Kalita et al., 2019). However, the intralobular duct is lined by columnar cells and not cuboidal cells in sheep (
Gemmel and Heath, 1973). The interlobular ducts were found between the lobules in the connective tissue septa. The interlobular duct was lined by a single layered cuboidal type of epithelium and is supported by numerous collagen and reticular fibres. These observations were in accordance with the findings in human pancreas (
Bloom and Fawcett, 1968) and in Zovawk pig
(Kalita et al., 2019). This duct showed distinct smooth muscle layer in its middle and surrounded by numerous connective tissue fibres as in buffalo pancreas (
Davinder and Gupta, 1999).
The islets of Langerhans were embedded within the exocrine portion of the pancreas. It appeared as pale stained rounded or oval or irregular areas between the darkly stained acini. They were separated from the acini by a thin layer of reticular and elastic fibers which were seen extending into the interior of the islets; but no distinct capsule encircling the islets was observed (Fig 3A and 3B). This is similar to observation in Zovawk pig (Kalita
et al., 2019). The islets were richly vascularized and the blood capillaries were enlarged forming cyst-like structure. The cells of islets were arranged in irregular branching and anastomosing cords separated by blood capillaries with delicate collagen fibres. Similar arrangement of islets cells were noticed in pancreas of domestic pig
(McGeddy et al., 2006), albino rat (
Fattah, 2008) and in Zovawk pig
(Kalita et al., 2019). Three different types of islets were observed
i.e. small, medium and large islets. The large islets were usually ovoid in shape and are found closer to the larger blood vessels and major ducts. The number of endocrine cells were more in large islets followed by medium and small. This is similar to observation in albino rat (
Rayaz, 2013). However, four different types of islets are noticed in pancreas of rat
viz., large sized (150μm and above), medium sized (75-150μm), small (50-75μm) and very small islets (
Hughes, 1946).
Mainly three types of cells were found in the islets
i.e. alpha (A), beta (B) and delta (D) cells. The alpha and delta cells occupied the peripheral region of the islet, whereas beta cells present mostly in the interior and only a few delta cells were found at intermediate portion (Fig 3C and 3D). This is similar to the finding in Zovawk pig
(Kalita et al., 2019) and in dog
(Kumar et al., 2024). The alpha cells were characterized by a pale cytoplasm, dense round granules and a pale nucleus. These cells appeared round to ovoid in shape, slightly larger than the beta cells and make up about 15 % of the total islet cell population as observation in camel (
Sultan, 1999) and in albino rat (
Rayaz, 2013). The beta cells were the predominant cell type. These cells were spherical in shape and constituted about 80 % of the total islet cell population. These cells had dark cytoplasm containing dense, round granules and a dark nucleus. The cells have round or oval-shaped nuclei. Finding is similar to observation made in Zovawk pig (
Kalita et al., 2019). However, the beta cells are polyhedral in shape in islets of rat, as described by
Patent and Alfert (1967). The delta cells were long, flattened or irregularly shaped with cytoplasmic processes. These cells were characterized by the presence of small granules and make up about 3 % of the total islet cell population as reported by
Elayat et al. (1995) in rat pancreas.
For histochemical studies, islets of Langerhans showed moderate activity for both Periodic acid Schiff (PAS) and Alcian Blue (pH-2.5) whereas the acini and the epithelial cells of the pancreatic ducts shows strong positive reaction for both Periodic acid Schiff (PAS) and Alcian Blue (pH-2.5) (Fig 4A and 4B). This is similar to observation in albino rat (
Rayaz, 2013). Moderate reaction for Alcian blue were observed in larger excretory ducts, but no affinity for Alcian blue in smaller pancreatic ducts of Japanese quail (
Sivakumar, 1997;
Das et al., 2001).
