Gosline J M, Shadwick R E
Department of Zoology, University of British Columbia, Vancouver, Canada.
J Exp Biol. 1996 Apr;199(Pt 4):985-97. doi: 10.1242/jeb.199.4.985.
The aortic arch and the descending aorta in the fin whale (Balaenoptera physalus) are structurally and mechanically very different from comparable vessels in other mammals. Although the external diameter of the whale's descending thoracic aorta (approximately 12 cm) is similar to that predicted by scaling relationships for terrestrial mammals, the wall thickness:diameter ratio in the whale (0.015) is much smaller than the characteristic value for other mammals (0.05). In addition, the elastic modulus of the thoracic aorta (12 MPa at 13 kPa blood pressure) is about 30 times higher than in other mammals. In contrast, the whale's aortic arch has a wall thickness/diameter ratio (0.055) and an elastic modulus (0.4 MPa) that are essentially identical to those for other mammals. However, the aortic arch is unusual in that it can be deformed biaxially to very large strains without entering a region of high stiffness caused by the recruitment of fully extended collagen fibres. Chemical composition studies indicate that the elastin:collagen ratio is high in the aortic arch (approximately 2:1) and that this ratio falls in the thoracic (approximately 1:2) and abdominal (approximately 1:3) aortas, but the magnitude of the change in composition does not account for the dramatic difference in mechanical properties. This suggests that there are differences in the elastin and collagen fibre architecture of these vessels. The descending aorta contains dense bands of tendon-like, wavy collagen fibres that run in the plane of the arterial wall, forming a fibre-lattice that runs in parallel to the elastin lamellae and reinforces the wall, making it very stiff. The aortic arch contains a very different collagen fibre-lattice in which fibres appear to have a component of orientation that runs through the thickness of the artery wall. This suggests that the collagen fibres may be arranged in series with elastin-containing elements, a difference in tissue architecture that could account for both the lower stiffness and the extreme extensibility of the whale's aortic arch. Thus, both the structure and the mechanical behaviour of the lamellar units in the aortic arch and aorta of the whale have presumably been modified to produce the unusual mechanical and haemodynamic properties of the whale circulation.
长须鲸（Balaenoptera physalus）的主动脉弓和降主动脉在结构和力学方面与其他哺乳动物的同类血管有很大不同。尽管鲸的胸降主动脉外径（约12厘米）与陆生哺乳动物根据比例关系预测的外径相似，但鲸的壁厚与直径之比（0.015）远小于其他哺乳动物的特征值（0.05）。此外，胸主动脉的弹性模量（血压为13千帕时为12兆帕）比其他哺乳动物高约30倍。相比之下，鲸的主动脉弓的壁厚与直径之比（0.055）和弹性模量（0.4兆帕）与其他哺乳动物基本相同。然而，主动脉弓的不同寻常之处在于，它可以双轴变形到非常大的应变，而不会进入由完全伸展的胶原纤维募集导致的高刚度区域。化学成分研究表明，主动脉弓中的弹性蛋白与胶原蛋白之比很高（约为2:1），而在胸主动脉（约为1:2）和腹主动脉（约为1:3）中该比例下降，但成分变化的幅度并不能解释力学性能的巨大差异。这表明这些血管的弹性蛋白和胶原纤维结构存在差异。降主动脉包含密集的腱状、波浪状胶原纤维带，这些纤维带在动脉壁平面内延伸，形成与弹性蛋白薄片平行排列并增强血管壁的纤维晶格，使其非常坚硬。主动脉弓包含一种非常不同的胶原纤维晶格，其中纤维似乎有一个贯穿动脉壁厚度的取向成分。这表明胶原纤维可能与含弹性蛋白的成分串联排列，这种组织结构的差异可以解释鲸主动脉弓较低的刚度和极高的可伸展性。因此，鲸的主动脉弓和主动脉中层单元的结构和力学行为可能都经过了改变，以产生鲸循环系统不同寻常的力学和血流动力学特性。
