Histological features of the aortic arch of the Baikal seal in the age aspect

The aim of the study is to investigate the histological features of the aortic arch wall in the Baikal seal. The object of the study was fragments of the aortic arch at its base, at the site of aortic dilation, before the origin of the left carotid artery, as well as the initial part of the thoracic aorta immediately after the origin of the left subclavian artery of kumutkans (n = 10), immature (n = 10) and mature (n = 10) seals. The study was carried out at the Department of Animal Morphology and Veterinary Sanitation of the Irkutsk State Agrarian University. Anatomical dissection and morphometry of various parts of the aortic arch were performed. Histological sections of the aortic arch, made on a microtome, were stained with hematoxylin and eosin, orcein, and Mallory staining. In all age groups, the maximum wall thickness was observed in the aortic bulb, then before the carotid artery originated, it significantly decreased, reaching the minimum value in the thoracic aorta. In addition, the wall thickness of the aortic bulb in immature seals increases by 1.46 times, and in mature seals - by 1.75 times compared to kumutkans. The largest number of elastic membranes was also found in the "aortic bulb" compared to other parts of the aortic arch. The intima of all areas of the aortic arch consists of a single layer of endothelial cells with flattened and oval nuclei and a subendothelial layer. The media of the aortic base and aortic bulb is formed by tightly arranged lamellar units consisting of elastic membranes, smooth muscle cells and collagen fibers located between them. In the aorta before the departure of the left carotid artery and the thoracic aorta, the elastic membranes become thinner, discontinuous, and the lamellar ones are more densely located in areas adjacent to the adventitia of the vessel. The outer shell of the aortic arch in all age groups is well vascularized, formed by loose connective tissue consisting mainly of collagen fibers with a small amount of thin elastic fibers and fibroblasts.