Introduction

The Iraqi black partridge (Francolinus francolinus) is a granivore in feed and belongs to the order Galliformes and the family Phasianidae (1). In vertebrates, there are two generally defined regions in the pancreas. The area responsible for releasing somatostatin, glucagon, and insulin hormones represents the endocrine part, while the area that secretes enzymes to the gastrointestinal tract represents the exocrine region (2). In birds, the pancreas is situated between the limbs of the duodenum, the descending and ascending (3). This avian gland is often lobulated, which contains just ventral and dorsal lobes in some species (4,5) or more than two lobes, as reported in another bird (6). Compared to those in vertebrates, the parenchyma of the bird pancreas comprises endocrine and exocrine parts that differ in their structures and size (7). Besides, two kinds of islets were detected in the endocrine area, including islets of beta and islets of alpha, which differ in their cells and function in early hatched geese (8). The third type of islets, called mixed, was located in chickens in addition to the other two types, and those three islets were found more often in the third and splenic lobe and rarely determined in the lobes of the dorsal and ventral one (9). Moreover, the necessary electrolytes and enzymes secreted from the exocrine mass that play an essential role in the digestive system and the hormones of endocrine islets that regulate blood sugar levels were observed in long-legged buzzards (10). The exocrine region units that include acini of secretory cells and the ductal system were investigated in red jungle fowl and goose (6,11).

 Because of the paucity of data about the pancreatic structures of partridges, especially histomorphometry and morphology, the current study was undertaken to describe those structures in the pancreas of Iraqi black Partridge macro and microscopically.

Materials and methods

Animals

 Twelve adult local partridges were used in the current experiment regardless of sex. The local market in the city of Baquba was the source of the experimental birds.

Experimental design

 Six birds were separated for macroscopic examination, and the remaining six were subjected to microscopic investigation. The birds, after being anesthetized with 25 mg/kg of ketamine, intramuscular injection (12-16), were slaughtered, and a line of incision in the ventral side of the abdomen was performed to view the viscera and to detect the pancreas attachments, situation, and its shape. The pancreas and its ducts were removed and washed with saline solution. Then, all macroscopic studies were conducted. A buffered 10% neutral formalin was used to fix the gland for 48 hours. A routine process was employed for fixed specimens, and by using a rotary microtome, a 5 µm thickness of series sections was obtained, which were then stained with routine and special stains (H&E, Gomori, and Masson's trichrome stain) (17-23). All microscopic examinations were conducted using a light microscope and the findings were recorded. Diameters of various kinds of ducts, islets, and capsule thickness were the microscopic parameters. A digital camera (image scope 9) with image processing software was used to accomplish the microscopic measurements (24). All data were analyzed statistically by using the software of SPSS.

Ethical approve

The scientific ethical committee in the College of Veterinary Medicine, University of Diyala was approved this study in ethical number VM.212.January2022.K&R, dated on 13/1/2022.

Results

Morphological outcomes

The macroscopic examination in the current work showed that the pancreas in the local partridge was a lobulated gland, pale pinkish, and found between ascending and descending parts of the duodenal limbs. It appeared ribbon-shaped, fixed in position with a ligament of pancreatic-duodenum. The gland is formed from four lobes: the ventral, splenic, dorsal, and third (Figure 1). The last one (third) is considered a crossing segment between the dorsal and ventral portions of the pancreas. It was seen that the lobes of this organ filled the space between duodenal limbs. The lobes of the pancreas were connected with duodenal loops through 3 pancreatic ducts (Figure 2).

Figure 1: Photograph of gross morphology of pancreas in local partridge shows the lobes of the pancreas: third lobe (black arrow), dorsal lobe (DL), ventral lobe (VL), splenic lobe (SL), which found between the ascending limb of the duodenum (AD) and descending limb (DD).

Figure 2: Photograph of gross morphology of pancreas in local partridge shows three ducts from the pancreas (black arrow), in addition to ascending limb (AD) and descending limb (DD) of the duodenum.

Histological outcomes

 Microscopic examination showed that the partridge's pancreas was surrounded by a capsule, which formed from cells of mesothelium resting on thin connective tissue. The average thickness of the capsule was 12.54± 0.65 µm (Table 1). Several septa emerged from this capsule and directed toward the parenchyma to divide the pancreas into several lobules. The thin connective tissue septum often contained the excretory duct, nerves, lymph, and blood vessels (Figure 3). A basic structure of pancreatic parenchyma in partridge was the exocrine units (serous acini) (Figure 4). Specifically, cells with a pyramidal shape, contain acidic granules and a spherical nucleus found at the basis of serous acini. In addition, the cavity of those acini contained small cells called the centraoacinar, which counts as a primary passage to the duct system. When liberated from the acini, the secretory materials could pass through the centroacinar to a series of ducts to reach the duodenum. The duct system comprised intralobular (intercalated), interlobular, and terminated by the main duct (Figure 5). The epithelial lining of those ducts was low cuboidal to flatted in the intercalated type, then converted gradually into simple cuboidal to columnar within the interlobular and main duct, respectively. The mean diameters of those ducts recorded 605.40± 15.38, 130.92±7.43, and 83.84± 4.63 µm in the main, interlobular, and intralobular ducts, respectively (Table 1). Significant differences in diameter were observed among various types of pancreatic ducts in partridge. Another composition, which was the least amount in the partridge pancreatic parenchyma, was the endocrine portion (Figures 3 and 4). The islets of Langerhans represent this part, which was scattered among the units of the glandular basic structure (Figure 3) and appeared in different shapes and sizes.

Three types of cells were detected in those islets, including beta, alpha, and delta cells (Figure 6). The most abundant cell in the islet was beta, distinguished by its small size and its nucleus large and dark with acidophilic cytoplasm. It was shown that the alpha cells presented in the least number, more significant than beta, and have nuclei as small pale (basophilic cells). The cells appeared irregular in shape with a large nucleus named delta. The diameters of Langerhans islets were recorded as a mean of 70.51±4.75, 65.75±4.1, 53.65±3.85, and 45.22±3.20 µm in the splenic, third, dorsal, and ventral lobes respectively (Table 2). Based on these measurements, a significant variation was detected in islet diameters among different pancreatic lobes.

Table 1: Microscopic parameters of the pancreas in Iraqi black partridge

٭Indicate significant difference (P<0.05) among types of pancreatic ducts.

Figure 3: Microphotograph of the pancreas in local partridge shows the capsule (C), a portion of exocrine (Exo), a portion of endocrine (End), intralobular duct (black arrow), interlobular duct (I-B), artery (A), Vein (V): Masson's Trichrome, 100 X.

Figure 4: Microphotograph of the pancreas in local partridge shows exocrine (Exo), endocrine (End), intralobular (brown arrow), interlobar duct (black arrow), H&E, 100 X.

Figure 5: Microphotograph of pancreas in local partridge shows exocrine (Exo), intralobular duct (black arrow), and interlobular duct (IB) lined with epithelium resting on connective tissue (M): Masson's Trichrome stain, 200 X.

Figure 6: Microphotograph of the pancreas in local partridge shows Langerhans islet in which beta cells (B) and alpha cells (A), in addition to exocrine part (Exo), intercalated (C) ducts. Gomori stain, X400.

Table 2: A mean diameter of pancreatic islets in different lobes of the pancreas in Iraqi black partridge

*Indicate significant difference in (P<0.05) among types of pancreatic Langerhans islets in different lobes.

Discussion

In the current experiment, the pancreas of the Iraqi black partridge appeared as a lobulated gland comprising four lobes: splenic, third, ventral, and dorsal. These results are consistent with a report of Kadhim et al. (6), who showed that the pancreas of red jungle fowl has four lobes, and with observations of Al-Sharoot (8) in the geese (Anser anser), but they do not correspond with those demonstrated in the native duck's study Mahmood et al. (25) and mynah's (Acridotheres tristis) pancreas (26). On the other hand, in our work, the gap between two duodenal arms was occupied with pancreatic lobes. These findings disagree with previous research of Beheiry et al. (27) in goose and in golden eagle (8) but were in line with the investigation of Kadhim et al. (6) in jungle fowl. It was found that the connective tissue of the pancreatic capsule in the current study was thin and sent septa to split the parenchyma into lobules. These observations are unlike the description of the thick capsule by Mobini and Aghaabedi (28) in turkeys, but they follow the findings of Mobini (11) in geese.

Microscopic inspection of the partridge's pancreas showed that two parts make up this gland: endocrine and exocrine areas. The serous acini are the main components of the primary exocrine segment, while Langerhans islets are distributed among the glandular regions and represent the part of endocrine, these results are in line in pigeon (29) and in Kestrel (3). Our study revealed that the tubule-acinar gland in partridge's pancreas has pyramidal cells called centroacinar in the center cells. These findings are similar to reports of Tarakci et al. (2) in Ostrich (Struthio camelus). It detected a set of ducts in the partridge, including intercalated, intralobular, and main duct. The epithelial lining of those ducts was low cuboidal to flatted in the intercalated type, then converted gradually into simple cuboidal to columnar within the interlobular and main duct, respectively. These results agree with numerous previous investigations in ducks (30), in golden eagles (5), and in jungle fowl pancreas (6).

The least amount in the partridge pancreatic parenchyma is the endocrine portion. The islets of Langerhans represent this part, which was scattered among the units of the basic structure and appeared in different shapes and sizes. Three types of cells were detected in those islets, including delta, alpha, and beta. These findings align with a description of Palmieri and Shivaprasad (31) in raptor bird's pancreas and in jungle fowl (6), who mentioned that the pancreatic islets in their studies contained three cell that led to different island types. The beta and alpha islets contained delta cells in mynah's pancreas (Acridotheres tristis) (26). On the contrary, the researcher Mobini (32) noticed that the pancreas in pigeons lacked mixed islets, while the small and large islets represented beta and alpha islets, respectively. The previous study conducted by Helmy and Soliman (33) showed the presence of mixed islets and alpha and beta islets in the pancreas of ostriches (Struthio camelus).

Conclusions

The present research gave a window on the histomorphometry and gross anatomy of the pancreas in local partridge and showed significant differences in the diameter of islets of Langerhans in various pancreatic lobes and pancreatic ducts measurements. Nevertheless, future investigations should conduct more examinations such as immunohistochemical and ultrastructure on partridge pancreas.

Acknowledgments

The writer is grateful to the faculty of Vet. Medicine, University of Diyala, Iraq, to help conduct the study.

Conflict of interest

The authors declare no quarrel of interest.