Macroscopical and microscopical studies of the common bile duct in reindeer ( Rangifer tarandus tarandus L )

T h e histological structure and secretory funct ion of the c o m m o n bile duct {ductus hepaticus communis) has not been previous ly described i n reindeer. Macroscopica l studies were thus per formed i n 25 reindeer to reveal the m o r p h o l o g y and topography of the ductus hepaticus communis and adjoining organs. H i s t o l o g i c structure of the c o m m o n bile duct was investigated i n 20 animals. O u r studies showed that the ductus hepaticus communis and pancreaticus j o i n about 2 c m before the duodenal opening to f o r m the c o m m o n duct. T h e c o m m o n bile duct is an elastic tube about 3 to 5 c m long and 2 to 3 m m th ick part ly surrounded by fat and pancreatic tissues. T h e w a l l of the duct, being about 1 m m thick by light microscopy, consisted of folded mucosa surrounded by connective tissue fibres and a serosal layer. D i s t a l l y , also muscular bands were seen. In some areas separate leucocytes and even lymphat i c nodules were present. Surpr is ingly pancreatic acini occurred i n certain areas of the w a l l , even i n close contact to subepithelial tissues. M u c o s a l ep i the l ium consisted of surface and glandular epithelial cells w i t h mucous secretion. N u m e r o u s intraepithelial globule leucocytes were identifiable w i t h i n the lamina epithelialis.


Introduction
The anatomy of the liver and main bile ducts varies among different animal species (Schache, 1907, Bevandic & al., 1967, Elias & Sherric, 1969, Dellman and Brown, 1976).The reindeer belongs to the family Cervidae, which do not possess a gall bladder.In the reindeer, bile secreted by the liver is thus directly conducted to the duodenum through the ductus hepaticus communis, the common bile duct (Akaevskij, 1939).The secretory function of the duct bile wall is not yet known.
In bovines, on the other hand, bile is stored in a gall bladder, the wall of which is rich in serous a.id mucous glands (Dellman and Brown, 1976).In cattle the original bile is thus concentrated and mixed by mucous fluids of the gall bladder and the wall of main bile duct is profoundly glandular (Rahko, 1971(Rahko, , 1973)).This paper describes the structure of the wall of the common bile duct in reindeer.

Materials and methods
Macroscopical studies were performed in 24 reindeer.One animal was selected for more thorough dissection of the inner organs to reveal the topography of the liver, pancreas and adjoining organs.
The tissue specimens of ductus hepaticus communis used in the light microscopical studies originate from 20 reindeer.Eight animals were slaughtered at the Reindeer Research Institute in Kaamanen outdoors at -30°C.12 reindeer were slaughtered in a slaughterhouse located in Savukoski in eastern Lappland.
Approximately 5-10 mm long specimens of ductus hepaticus communis, surrounded by fat and pancreatic tissues, were cut into small tissue blocks, which were soon transferred into the different fixatives.Care was taken to prevent freezing of the tissue specimens.
Six specimens were fixed in diluted formaldehyde solution (25 %) buffered at pH 7 by phosphate buffer (fixation time 4 days).Additional six specimens were fixed in Bouin' s solution for one day, then transferred into 70 % alcohol.Furthermore, 14 specimens were fixed during 1 to 4 months in 4 % paraformaldehyde in 0.1 M phosphate buffer containing 0.1 % sodium azide (NaN3) and 0.05-0.1 % glutaraldehyde.
The material was embedded in paraffin in the usual manner, sectioned at 4 microns and routinely stained with haematoxylin and eosin (HE).

Macroscopical studies
The common bile duct appeared as a 2-3 mm thick elastic tube between the liver and oral part of the duodenum.It was 3-5 cm long, white and thin-walled.The duct was partly surrounded by fat and pancreatic tissues.No papilla was observed around its duodenal opening.At slaughter when the duct was cut the mucosa of the stump appeared to be yellow in colour near the hilus of the liver.
The ductus pancreaticus connected with the common bile duct at about 2 cm before the duodenal opening.

Microscopical studies
The wall of the common bile duct appeared to be about 1 mm thick by microscopy.The outer layers were surrounded by a serosal coat and consisted of circular connective tissue fibres.Smooth muscle layers were detected in only distal sections of the duct near the duodenum.In some areas pancreatic tissues were observed in the wall of the duct (Fig. 1).
The inner layers of the wall consisted of folded mucosal tissues with epithelial surface and glandular structures surrounded by a loose connective tissue network of lamina propria (Fig. In the lamina propria, dispersed granulocytes and lymphocytes were present and also prominent accumulations of lymphatic cells were observed (Fig. 3 and 4).
The epithelium was composed of tall columnar epithelial cells with basal, rounded and regular nuclei (Fig. 5 to 7).A few goblet cells were located within lamina epithelialis.The cytoplasm of the epithelial cells was pale in HEstained sections, especially in the deep glands.In mucous glands the cytoplasm of epithelial and goblet cells was ballooned by mucous secretions.Mucus also was present freely in the lu¬ mina of the glands.
Numerous globule leucocytes were present in superficial and glandular epithelium.The cells were located basally within the epithelium.They were identified on the basis of large eosinophilic rounded globules.The nuclei were chromatin-rich and rounded being quite similar in appearance to those of the lymphocytes.Eosinophilic granulocytes were easily identifiable in proprial tissues (Fig. 8) while mast cells were difficult to detect in HE-stained sections.Mast cell granules appeared small and faintly-stained.
All the fixatives used were suitable for histologic studies.However, our impression was that Bouin's solution and paraformaldehyde preserved the tissues particularly well.

Discussion
The results of the present study showed that morphological characteristics of the wall of the common bile duct in Finnish reindeer are largely similar to those in other animal species (e.g.

McMinn
and Kugler, 1961, Dellman and Brown, 1976, Rahko 1971, 1973).The duct is short, elastic and thin-walled with smooth mucosal folds consisting of epithelial and glandular structures.Connective tissue fibres of lamina propria are loose while the outer layers of the duct contain circular mesenchymal elements with smooth muscle fibres in distal parts of the duct.
The entering of the ductus pancreaticus into bile duct to form the ductus communis was observed as previously described by Akaevskij (1939).This is typical in sheep and goats, while in most domestic mammals the pancreatic and hepatic ducts are separate anatomic structures (Schmidt and Ivy, 1937, Elias and Sherrick, 1969, Dellman and Brown, 1976).
A new finding not previously described is the extension of pancreatic acini into proprial tissues of the bile duct (Figure 1).The significance of this peculiar anatomical feature is unclear to the authors.Further studies are needed to elucidate if the pancreatic acini described are ectopic pancreatic tissues or normal projections in the form of caput biliaris in additon to the previously described capiti duodenalis and omentalis.
Electron microscopic studies showed that the ultrastructural features of pan-creatic acini of bile ductal walls appear similar to those in normal acini of mammalian animals (Rahko and Nikander, 1990).
Lamina epithelialis contains numerous globule leucocytes (Gregory, 1979, Nikander andRahko, 1990).The cell has not previously been identified in reindeer.The globule leucocyte is known to occur within different epithelial tissues of many other animal species and in man.The frequency with which the cell appears, however, is usually associated with parasites e.g.Gregory, 1979.The animals in the present study were treated with anthelmintica in the preceding autumn and were thus considered to be free from clinical helminthosis (Holmstrom & al., 1989).Further studies are to be performed in order to elucidate the frequency of globu 1 e leucocytes in Finnish reindeer.

Fig. 3 .
Fig. 3.The cytoplasm of epithelial cells in the glands is filled with mucous.Round cells and eosinophilic granulocytes are present in submucosal areas (arrows).HE, x 256.

Fig. 4 .
Fig. 4. Cross section through the wall of common bile duct, showing a prominent lymphatic nodule.HE, x 256.

Fig. 5 .
Fig. 5.The cytoplasm of epithelial cells is pale in the deep glands.Note the structural difference between intraepithelial globule leucocyte (GL) and mast cell (MC) located in the lamina propria.HE, x 1040.

Fig. 8 .
Fig. 8. Infiltration of eosinophilic granulocytes (arrows) surrounded by connective tissue elements.Compare the appearance of nucleus and intracytoplasmic granules of eosinophilic granulocytes to those of the globule leucocytes illustrated by Figures 5 to 7. HE, x 1040.