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Revista chilena de anatomía

Print version ISSN 0716-9868

Rev. chil. anat. vol.19 n.2 Temuco Aug. 2001

http://dx.doi.org/10.4067/S0716-98682001000200005 

SYSTEMATIZATION OF THE ARTERIES IN THE SPLENIC HILUS
OF THE ARMADILLO (Dasypus novemcinctus, L.)

SISTEMATIZACIÓN DE LAS ARTERIAS EN EL HILIO ESPLÉNICO
DEL ARMADILLO (Dasypus novemcinctus, L.)

* Bruno Cesar Schimming & **Mara Alice Fernandes de Abreu

SUMMARY:  The authors have conducted a anatomical study of armadillo spleen's arterial vascularization, in respect of its origin, their branches and the pattern vessels' distribution. Therefore, was related in special, the arterial behaviour of the extra-hilaris vessels of the splenic artery. These observations were aggregated and reported, and all data are compared with those reported in the literature.  

        KEY WORDS: 1. Anatomy; 2. Splenic artery; 3. Armadillo; 4. Spleen.

** Laboratory of Anatomy, Faculty of Health Sciences, University of Marília, UNIMAR, São Paulo, Brazil.
** Department of Biological Sciences, Faculty of Sciences of Bauru, UNESP, São Paulo, Brazil.

INTRODUCTION

       Armadillos are considered as relictual mammals important as model for biomedical studies, since Kirchheimer & Storrs (1971) reported the susceptibility of the armadillo to Mycobacterium leprae. They contain adaptative and primitive characteristics in both anatomical and physiological aspects (Galíndez et al., 2000).

       Information about the Mycobacterium leprae found in the armadillos is abundant. Studies of the ¨naturally occurring leprosy-like disease of wild armadillos¨ establish that the causative bacillus is genetically identical to M. leprae from human sources, and thus the disease is a zoonosis, sylvatic leprosy (Folse & Smith, 1983; Meier et al., 1983). Therefore, armadillos developed experimental disseminated leprosy. Opromolla et al. (1980) inoculated M. leprae in the armadillos in captivity and bacilli were found in large quantities in various organs like the skin, lymph nodes, liver, kidneys and spleen. Balina et al. (1985) also studied experimental reproduction of leprosy in armadillos and suggested that acid-fast bacilli are found in the skin, nerves, spleen, lymph nodes, lungs, meninges, and striated muscle.

        The spleen is a highly vascular organ that have several diverse functions, e.g., stores and concentrates the erythrocytes and releases them during times of need; filters the blood, and removes the worn-out erythrocytes from the circulation; and produces many of the lymphocytes and probably most of the monocytes (Evans & Christensen, 1979).  

       Arterial vascularization of spleen of various species of the mammals has been studied, as rat (Braithwaite & Adams, 1956), cat (Holzchuh, 1977), dog (Gupta et al., 1978a), goat (Gupta et al., 1978b), buffalo (Gupta et al., 1978c; Abreu Rays, 1982), sheep (Ocal & Takci, 1991), and opossum (Silva, 1999).  

       On the other hand, there are only few reports about armadillo spleens. Hayes (1970) reported the structure of the ellipsoid sheath in the spleen of the armadillo, by way of light and electron microscope. Galíndez et al. described the splenic histology and cytology of the «mulita» (Dasypus hybridus). On the basis of the above infor-mation, and know that the spleen is a organ that may presents leprosy bacilli, we describe the arterial supply of the armadillo spleen, and compared it with others species available in the literature.

MATERIAL AND METHOD  

       This study used ten adult armadillos (Dasypus novemcinctus, L.), males and females, weighing 2 to 4 kg, which had been destined to experimental studies on leprosy, but did not survive the period of adaptation to captivity routinely schedulet at the animal house of the Lauro de Souza Lima Institute (Bauru, S.P., Brazil).  

       We cannulated the right common carotid artery. Then used a tube with proper caliber and then coloured latex Neoprene 650 ® (Du Pont do Brasil S.A.) was injected towards the caudal direction. The animal was fixed in a 10% formalin solution. The abdominal cavities were exposed and the dissections were performed macroscopically and then under the stereoscopic microscope at 2x to 16x magnification; making possible to analyze the distribution of splenic artery and to identify their branches.

         The nomenclature used in this study was according to the pattern established by Gupta et al. (1978a.,b) for dog and goat spleens, and by Schaller (1999) (International Committee on Veterinary Gross Anatomical Nomenclature).

RESULTS  

       The armadillo spleen is supplied by the terminal branches of the splenic artery. We can considered that as the splenic artery approaches the spleen it divides into a terminal branches. These branches, pass through the long hilus, and undergo several subdivisions, finally giving the hilar arteries which penetrate into the spleen.     

        The spleens showed pedicles consisting of 2 to 4 extra-hilar vessels, most of which were primary and only a few secondary order, predominating those with three extra-hilar vessels, that are destined to the dorsal, intermediate, and ventral portions of the spleen after sending branches to nearby structures (Figs. 1, 2, 3 and 4).  

       Generally, each primary branch supplied a particular portion of the spleen without any anastomoses between the hilar vessels of neighbouring regions. Before the primary branches penetrate into the hilum of the spleen (hilar arteries), they usually, undergo successive subdivisions. The number of these penetrating arteries varied. The pattern of arterial splenic vascularization has been summarized in the Table I.

         The first pattern of the splenic pedicles in the armadillo, it was observed in the three specimens studied, the splenic artery divides into two primary branches, a small ventral and a large dorsal one (Fig. 1). Commonly the splenic artery trifurcated before entering the hilus, and gives three primary splenic branches, a dorsal, an intermediate and a ventral one (Fig. 2). These primary branches can or can not arise directly from the splenic stem. It was occurred in five animals. Thus, this pattern was more frequent in the armadillo spleen.

       It was observed in one specimen, a third pattern of division of the splenic artery. The splenic pedicles is formed by four extra-hilar branches, three primary branches: a ventral, a dorsal and a polar ventral, and one secondary branch, dorsal-intermediate (Fig. 3). For its origin we refer to the division of the splenic artery. Therefore, in other case, the splenic artery showed three extra-hilar branches, two primary, a dorsal, and a ventral-intermediate, and one to the ventral extremity. Two secondary branches arise from ventral-intermediate branch, a intermediate, and a ventral branches. Several dorsal branches arise from the dorsal branch (Fig. 4).

Fig. 1. The splenic artery (s) gives rise to the two primary branches: ventral (v), dorsal (d), and a secondary branch intermediate (i). Therefore, it can see the gastric branches to the greater curvature of the stomach (g).

 

Fig. 2. The splenic artery (s) provides three extra-hilar primary branches: ventral (v), intermediate (i) and dorsal (d), and several gastric branches (g), and a pancreatic branch (p).

  Polar arteries were observed between the terminal branches of the splenic artery clearly in the two specimens. These polar arteries supplied a ventral extremity of the armadillo spleen. In the all patterns of the splenic artery division, it provides various number of small pancreatic branches without further specification. Therefore, several gastric branches arise from the stem of the splenic artery or from its branches. One of these are called left gastroepiploic artery that only reaches the stomach at about half of the greater curvature. The proximal portion is supplied by the short gastric arteries (Figs. 1, 2, 3 and 4).

      

Table I. Terminal branches of the splenic artery (hilar arteries).

Primary branches             % Secondary branches           %
Ventral              
 40.91
Ventral      28.13
Intermediate             
9.09  
Intermediate  28.13
Dorsal-intermediate   
4.55
Polar-ventral  9.37
Dorsal  
45.45     
Dorsal-intermediate   3.12
    Dorsal 31.25
Total     100.00 Total  100.00

 

Fig. 3. Showing three primary branches of the splenic artery (s): two ventrals (v) and dorsal (d) and one secondary branch dorsal-intermediate (di). The pancreatic (p) and gastric branches (g) are seen.

 

Fig. 4. Three divisions of the splenic artery (s), two primary branches, ventral-intermediate (vi) and dorsal (d) and a third branch to the ventral extremity (ve). Gastric (g) and pancreatic branches (p) are present.

DISCUSSION  

       The name ¨splenic¨ artery is misleading for a vessel that supplies besides the spleen also a great part of the stomach and of the pancreas (Vandamme & Bonte, 1986). The pattern of the splenic artery have been described in various mammals including dog (Gupta et al., 1978a), goat (Gupta et al., 1978b), buffalo (Gupta et al., 1978c) and sheep (Ocal & Takci).

        According to Silva & Martins (2000), the division of the spleen is made on the basis of arterial vascular distribution and of segmental arterial distribution through the organ, characterizing a variability in number of extra-hilar branches originating from the splenic artery.

         The armadillo spleen presents a hilus with a pedicle formed by 2 to 4 extra-hilar vessels. On the other hand, Abreu Rays reported that the buffalo spleen presents 2 to 5 vessels in the hilus.

       This extra-hilar vessels were called primary and secondary vessels. Each primary branch supplied a definite region of the spleen without any apparent anastomoses between the vessels of adjacent regions. Gupta et al. (1978b) and Ocal & Takci described similar observations in the goat and sheep spleens. Gupta et al. (1978b) reported an avascular plane between the branches of two main divisions of splenic artery. To these authors, this avascular plane was parallel to the long axis of the goat spleen. The splenic branches are considered terminal arteries forming no anastomoses (Mackenzie et al., 1941), except for some intrahilary shunts (Clausen, 1958).  

      The primary splenic terminal branches may give off as many as some generations of branches before they penetrate into the splenic hilum. However, most of the ultimate branches are tertiary divisions. The number of hilar branches in our study was highly variable, as reported by García-Porrero & Lemes (1988).

         Our observations demonstrate clearly that the splenic artery most frequently divides into three primary branches, a ventral, an intermediate and a dorsal. This feature is also found in the buffalo spleen (Abreu Rays). The incidence of triple primary branching is bigger than that reported by Gupta et al. (1978a,b,c); García-Porrero & Lemes and Ocal & Takci.

        However, this work reports that the splenic artery also can divides into two primary branches, although in a lower incidence that reported previously by Gupta et al. (1978a,b,c) and Vandamme & Bonte. Generally, this pattern of splenic artery division has been more found in the literature.

         The others patterns observed by us, which in one case presents a polar ventral, ventral, dorsal and dorsal-intermediate; and in one specimen the splenic artery divided into dorsal, ventral-intermediate and dorsal branches, also were describe in the buffalo spleen by Abreu Rays.

         In some instances, distinct polar ventral arteries were seen in the armadillo. This feature is notably lower than that found in the literature. Since Gupta et al. (1976) did not mention the existence of polar vessels, it is possible that in their study a polar artery was considered as a terminal primary branch. García-Porrero & Lemes mentioned polar arteries. The above-mentioned authors found a superior polar and a inferior polar arteries. To these authors, sometimes it was not easy to identify an artery as polar, and it is possible that some of this difference is due to the variability inherent in subjective interpretations. The polar arteries are not accessory vessels, but instead are also segmentary arteries.

         Pancreatic and gastric branches also are divisions of the splenic stem. These observations are in agreement with the studies of Vandamme & Bonte.

         Based on the observation of the pattern of the terminal and polar splenic branches, selective arteriographs and corrosion casts, García-Porrero & Lemes proposed that the human spleen is divided in arterial segments and subsegments. Segments are the territories corresponding to both the primary branches of the splenic artery (primary segments) and the polar arteries (polar segments). Subsegments are the territories corresponding to the extrasplenic subdivisions of the primary branches and the polar arteries. The number of segments and subsegments are highly variable, as reported by Gupta et al. (1978a,b,c) and Ocal & Takci (1991).

         Generally, the armadillo spleen presents three distinct regions: dorsal, ventral and intermediate, according to the more frequent pattern of the division of the splenic artery, similar to the cat spleen (Holzchuh). We not called these regions of vascular segments, because we did not use another technique for the recognition of splenic vessels since latex injection and dissection.

RESUMEN: Se realizó un estudio anatómico para caracterizar la vascularización arterial del bazo en el armadillo, estudiando origen, trayecto, división y distribución. El objetivo de este estudio fue la búsqueda y análisis de las variedades anatómicas  de las ramas extra-hilio de la arteria esplénica. Las características son comparables con las interpretaciones previas.

      PALABRAS CLAVE: 1. Anatomía; 2. Arteria esplénica; 3. Armadillo; 4. Bazo.

Correspondence to:

Prof. Dr. Bruno Cesar Schimming
Laboratory of Anatomy
Faculty of Health Sciences
University of Marília _ UNIMAR
Av. Hygino Muzzy Filho, 1001
Marília _ São Paulo
Cep 17525-902
BRAZIL

E-mail: schimmin-fcs@unimar.br

Recibido : 16-04-2001
Aceptado: 25-05-2001

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