Structural particularities of subclavian arteries in lamb

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1 Structural particularities of subclavian arteries in lamb V. MICLĂUŞ (1), D. CSIBI (2), V. RUS (1)*, C. MARTONOS (2), F. RUXANDA (1), A. DAMIAN (2) 1 Departments of Cell Biology, Histology and Embryology, Faculty of Veterinary Medicine, University of Agricultural Sciences and Veterinary Medicine, Cluj-Napoca, Romania 2 Departments of Comparative Anatomy, Faculty of Veterinary Medicine, University of Agricultural Sciences and Veterinary Medicine, Cluj-Napoca, Romania *Corresponding author USAMV Cluj-Napoca Histology Calea Manastur, 3-5, Cluj-Napoca, Romania Cluj-Napoca Romania vasilerus2002@yahoo.com Keywords. Subclavian arteries, lamb, structure. Summary Samples from the left and right subclavian arteries were harvested from three hybrid Merino lambs in order to conduct histological investigation. We observed that these arteries present muscular isles on section, disposed at a certain distance one from another, in the external half of Folds emerge when the muscle cells contract, which project into the lumen, thus reducing the caliber of the lumen. It seems that the role of this muscle isles is to adjust the blood quantity in the areas irrigated by these arteries, participating in the preferential distribution of blood. The lumen is open when animals move and feed, and during rest and over night their lumen diminishes, thus laying off blood which will be redirected to more solicited areas, especially the digestive tube. Introduction The subclavian arteries irrigate the anterior limbs, the neck, the cranial and ventral parts of the thorax (Campos et al., 2010; Dyce et al., 2010; Budras et al., 2011). They originate in the brachiocephalic trunk in most of the species, but there are also exceptions, such as in swines and carnivores, where the subclavian artery detaches directly from the aorta. The subclavian arteries emit three dorsal branches: costocervical artery, deep cervical artery, vertebral artery and three ventral branches: internal thoracic artery, omocervical artery and external thoracic artery (Damian, 2001; Mireşan and Constantinescu, 2012). Large arteries, also termed as elastic arteries continue with passage segments towards the muscular arteries, also named transitional or mixed arteries, which contain isles of smooth muscle cells in tunica media, separated by elastic lamellae (Raica et al., 2002). In horse, the passage from elastic to muscular arteries is abrupt, which represents an exception (Adlersberg et al., 1957). We found a few studies in the specialty literature concerning the structural characteristics of the subclavian arteries in domestic animals and they were conducted only on certain species. Thus, Damian et al. (2014) claimed that the subclavian arteries in pig are transitional type, with a 50-50% ratio between the elastic and muscular components in The subclavian arteries belong to the elastic type in humans (Gussenhoven et al., 1989), but also in black Bengal goats (Capra hircus) in Bangladesh (Awal et al., 1999). Considering 35

2 the fact that the specialty literature highlights differences from one species to another, we considered appropriate to conduct histological investigation on subclavian arteries in lambs. Materials and methods Animals taken into study were represented by three hybrid Merino lambs, 3 months old, sacrificed by the owner for own consumption. On this occasion, fragments from the left and right subclavian arteries were harvested in order to conduct histological investigations. The samples were promptly fixed in Stieve s solution for 24 hours long, then dehydrated with ethanol, clarified in n-butanol and embedded in paraffin. 5 µm thickness sections were made and stained with Goldner s trichrome and Verhoeff staining procedures. The slides were examined with an Olimpus BX41 light microscope equipped with a digital Olympus BX41 camera. The captured images were edited in Adobe Photoshop CS2 V Program. There are a few elastic fibres in the muscle isle which partially or entirely cross the isle, but their thickness is significantly smaller in comparison to the elastic lamellae present in tunica media s thickness (Fig. 5). Fig. 1. Right subclavian artery (Goldner s tricrome) Black arrow tunica media; red arrow muscle isle in tunica media; blue arrow folds that project into the lumen. Results and discussions The histological examination highlighted the fact that tunica media of the subclavian arteries did not present the same thickness throughout its entire circumference, which made its lumen appear sinuous because of certain folds formed from tunica media and intima. The aspect was present and comparable in the right (Fig. 1) as well as the left subclavian artery (Fig. 3). There were conglomerations of smooth muscle cells which appeared as a circumscribed muscle isle in tunica media s thickness on section. The muscle isles were disposed at a certain distance one from the others, occupying a great part of the tunica media s thickness, starting from tunica adventitia (Fig. 1, 3). The presence of muscle conglomeratates grouped in isles is obvious on Verhoeff s elastic stain, which clearly differentiate the muscle component from the elastic one (Fig. 2, 4). Fig. 2. Right subclavian artery (Verhoeff s stain) Black The arrangement of muscle fascicles as isles on section, in the case of subclavian arteries represents a particular aspect. When the muscle cells in the isle contract, a fold emerges into the lumen of the vessel. We must point out that tunica media participates entirely along with tunica intima in forming these folds, thus they are large and relatively high. We must not mistake these folds for the situation existent in muscular arteries and 36

3 some elastic arteries which present small folds towards the lumen, formed by the internal elastic membrane and tunica intima (tunica media does not participate in forming these folds). Fig. 3. Left subclavian artery (Goldner s tricrome) Black arrow tunica media; red arrow muscle isle in tunica media; blue arrow folds that project into the lumen. Because of the fact that the muscle isles are disposed at a certain distance one from another, various large folds orientated towards the lumen appear by contraction of the muscle cells in their structure. The prominent folds transiently reduce the lumen of the vessel, conditioning to a certain extent the blood flow. This arrangement as muscular isles is functionally comparable to a certain extent to the aspect present in arteries with pads and it is possible that the contraction effect is comparable, namely the controlled reduction of the vascular lumen. The situation is not identical because the arteries with pad-like folds are small arteries (arteriols) in which the high fold (pad-like fold) closes the lumen for a certain period, thus adjusting the local blood flow and pressure (Diculescu et al., 1971). In lambs, this folds that resemble the pads appear in large caliber arteries (subclavian arteries) whose lumen is not obstructed during the fold formation, but proportionally reduced depending on the fold number and amplitude. In this context, the blood flow is not transiently interrupted like in arteries with pads, but reduced for a certain period of time by changing the vascular lumen. It is possible that this aspect is important because of the possibility for a controled distribution depending on the necessities, and the modification of the lumen caliber offers such possibilities. This aspect might be highly linked to the preferential distribution of the blood towards the following arterial segments. Fig. 4. Left subclavian artery (Verhoeff s stain) Black Fig. 5. Left subclavian artery (Verhoeff s stain) Black By forming and fading the folds, a larger or smaller amount of blood can pass towards the vessels that irrigate the anterior limbs, 37

4 neck, cranial and ventral part of the thorax. We can only express a point of view regarding the functional importance of the preferential distribution of blood towards these arteries. We consider that the lumen of the vessels is widely open and allows the passage of a large quantity of blood towards the above-mentioned arteries when the animals feed and the irrigated areas by these vessels are solicitated. During rest and at night, these areas are not solicitated, and blood is needed elsewhere, especially in the digestive area, the fact that the digestion is more complex and soliciting in herbivores being well known. By contraction of the muscle cells in the isles, large folds are formed and the arteriolar lumen significantly decreases. Consequently, the blood quantity directed in the vessels that irrigate the anterior limbs, neck, cranial and ventral part of the thorax is reduced. The blood excess is preferentially redistributed towards more solicited areas for a certain period of time. Adjusting the blood flow according to the functional needs of the organs is a known phenomenon, which in all mammals is ensured by small and medium arteries that can preferentially distribute blood to different organs depending on the needs, which is why these vessels are also called distributing arteries (Lesson et al., 1985). Besides the distribution arteries known in all mammal species, in lambs we can encounter this particular situation in which the subclavian arteries are included (they fall under large arteries cathegory, not small and medium ones). It seems like the lambs have a greater need for the preferential distribution of blood towards certain organs in order to ensure the functional necessities during maximum solicitation, in comparison to other mammals. Because of the fact that they are not temperamental animals and they are not more solicited from any point of view in comparison to the majority of the mammal species, in our opinion there is only one explanation for this particularity, namely the existence of some organs which are not present in other species. The only organs present in lambs and absent in other species are the forestomachs, large organs with a soliciting activity. Ruminants intake large quantities of food that needs special, durable and soliciting processing, which is why there is a great necessity for particularly increased blood flow towards the digestive tube throughout the digestion process. The involvement of the subclavian arteries in the preferential distribution of the blood towards the digestive system during its solicitation is rather indirect, not direct. By reducing the blood quantity that flows through their lumen during rest, a larger quantity of blood remains available which can be distributed to the digestive system organs. The preferential distribution of blood towards the digestive system is stil ensured by the distributing arteries, the subclavian arteries making a certain blood quantity available which can be used as an addition throughout the intense digestion process. We do not have other evidence to sustain this point of view besides the particular morphological aspects we encountered in the subclavian arteries in lamb. Nevertheless, the statement seems logical, because in lambs the food collection and the most intense moments of the digestion process do not overlap. This way, the organism has the possibility to efficiently distribute the blood towards the solicited areas depending on the situation. Conclusions The subclavian arteries in lamb present particular aspects in tunica media, which contains various muscular isles on section, situated at a certain distance one from another, especially in its external third. Different height folds form towards the lumen of the vessel when the muscle cells in the isles contract. All the folds reduce the diameter of the vessel to a certain extent. Through their disposition, all around tunica media, they modify the vascular lumen between large limits which suggests that their 38

5 function would be to adjust the blood quantity which is allowed to pass to the areas irrigated by these vessels. When the animals move and feed, the subclavian arteries keep their lumen open because the areas they irrigate are solicited, References Adlersberg L.; Brătianu S.; Crişan C.; Gündisch M.; Hagi Paraschiv A.; Niculescu I.; Râmniceanu C.; Ţupa A., Histologie, Volumul I, Editura Medicală, Bucureşti,1957. Awal M.A., Prodan M.A.A., Asaduzzaman M., Kurohmaru M., Histological studies on the arterial walls of main arteries supplying the mammary glands of black Bengal goats (Capra hircus) in Bangladesh, Veterinarski Arhiv, 69(6): , Budras K.D., Habel R.E., Mulling C., Greenough P.R., Bovine Anatomy, Second extended edition, Ed. Schlutersche, Germany, 2011 Campos R., Araújo A.C.P., Azambuja R.C., Ramos colaterais do arco aórtico e suas principais ramificações em nutria (Myocastor coypus), Acta Scient.Vet.,38(2): , Damian A., Anatomie comparată, Sistemul cardiovascular, Editura AcademicPres, Cluj- Napoca, 2001 Damian A., Miclăuş V., Crişan M.I., Irimescu I., Rus and during rest and over night, their lumen diminishes, laying off blood which will be redirected to the digestive system. V. Tuns F., The structural features of several large arteries in pigs, Anat., Histol., Embriol.,. 43(Supll 1), Diculescu I., Onicescu Doina, Rîmniceanu C., Histologie, Vol. II, Ed. Didactică şi Pedagogică, Bucureşti, Dyce K.M.; Sack W.O.; Wensing C.J.G., Textbook of Veterinary Anatomy, Fourth Edition, Saunders, an imprint of Elsevier Inc., United States of America, p , 432, 810, 2010 Gussenhoven W.J.; Essed C.E.; Frietman P.; Mastik F.; Lancee C.; Slager C.; Serruys P.; Gerritsen P.; Pieterman H.; Bom N., Intravascular ecographic assessment of vessel wall characterstics: a correlation with histology, International Journal of Cardiac Imaging, 4: , 1989 Leeson R.C., Leeson T.S., Paparo A.A., Textbook of histology, W.B. Saunders Company, Philadelphia, 1985 Mireşan V., Constantinescu R., Anatomie comparată şi Histologie, Ed. Academicpres, Cluj-Napoca p , 2012 Raica M., Mederle O., Căruntu I-D, Pîntea A., Chindris A-M., Histologie teoretică şi practică, Ed. Brumar Timişoara,