Distribution and functional significance of muscle islands in the tunica media of the aorta in the goat (Capra hircus)

Abstract

The presence of muscle islands in the tunica media of elastic arteries has been reported in both large and small ruminants. According to some authors, these islands can have a certain influence on the physical-mechanical properties and the pattern of diseases in the aortic wall. The aim of the current study was to highlight the muscle islands and their distribution throughout the aortic segments in the goat and to understand the reason why they are present only in certain species of animals, including the goat. Gross anatomical dissection of the aorta was performed and samples from the following segments were harvested for histological investigations: ascending aorta, aortic arch, descending thoracic aorta and descending abdominal aorta. The muscle islands in the wall of the aortic segments are formed by smooth muscle cells interconnected with connective tissue and are preferentially vascularized by vasa vasorum and innervated by nervi vasorum. The aorta in the goat presents polymorphic muscle islands, arranged in the outer two thirds of the tunica media in the ascending aorta, the outer half at the level of the aortic arch and the descending thoracic aorta, but they are absent in the descending abdominal aorta. Their presence completes the windkessel function of the aortic wall, thus constituting an additional pump necessary to propel the blood towards the abdominal viscera, which in goats, in addition to those present in monogastrics, also contain three large and very active organs, namely the rumen, the reticulum and the omasum.