A Lamellar Unit of Aortic Medial Structure and Function in Mammals

Abstract

The close association of elastin, collagen, and smooth muscle in the mammalian aortic media results in viscoelastic properties that account for many of its static and dynamic mechanical features. The structural components of the media are precisely oriented in concentric layers, or lamellar units, of fairly uniform composition. A comparative study of the adult thoracic aorta in 10 mammalian species, including 15 canine breeds, showed that the number of lamellar units in the media of adult mammalian aortas is very nearly proportional to aortic radius regardless of species or variations in measured wall thickness. Estimated wall tensions ranged from 7,820 dynes/cm in a 28-g mouse to 203,000 dynes/ cm in a 200,000-g sow, but the average tension per lamellar unit of an aortic media was remarkably constant regardless of species, ranging from 1,090 to 3,010 dynes/cm. The findings suggest that the elastin lamella and the contents of its adjacent interlamellar zone represent the unit of structure and function of the mammalian aortic wall.ADDITIONAL KEY WORDS structure-function elastin collagen wall tension comparison of 10 species• The mammalian aortic wall contains smooth muscle cells and the fibrous proteins collagen and elastin. Smooth muscle proteins account for about 20? of the dry weight of the media; collagen and elastin together account for about 60% (1, 2). There is usually more elastin than collagen in the thoracic aortic segment and more collagen than elastin in the abdominal segment. However, the total fibrous protein concentration is nearly the same for both segments and is remarkably constant for adult mammalian aortas, regardless of species (1, 2). At physiological distending pressures, aortic elastin and collagen fibers and smooth muscle cells are precisely

New insights into elastic fiber assembly

“…Surprisingly, they also have an increased number of lamellar units in the arterial wall (Li et al, 1998b;Faury et al, 2003) (a lamellar unit is defined as a layer of elastin with its associated SMCs). Lamellar units are established in early development during formation of the vessel wall and lamellar number is linearly related to wall tension in most mammals (Wolinsky and Glagov, 1967). Our recent morphologic studies of developing eln2/2 and 1/2 aorta show that the changes in wall structure occur in the last few days before birth (between embryonic day 18 [E18] and postnatal day 0 [P0]) just as the pressure and blood flow are significantly increasing.…”

Hereditary haemorrhagic telangiectasia: Pathophysiology, diagnosis and treatment

“…For vessels to support arterial pressure, interspecies comparisons indicate that there is an optimal wall thickness/ lumen radius ratio to minimise wall stress. 94 When human veins are transplanted into arterial settings, adaptation to that ratio normally occurs, accompanied by increasing wall thickness. 95 In HHT, however, assumption of a more arterial phenotype following establishment of the AV communication is not observed.…”

Changes in aortic medial elastic structure at different sites in the primates Erythrocebus patas, Macaca irus and Callithrix jacchus

“…Tension stresses in the vessel wall are apparently largely responsible for the medial structure which develops (see Berry, 1973) and Wolinsky & Glasgov (1967) have pointed out that the mean tension/lamellar unit is around 2000-400 dynes/em. With the progressive fall in aortic diameter tension in the wall diminishes since T=Pr where T is the total tangenta\ tension in dynes/em length of vessel, P is the pressure in dynes/em 2 and r is the radius in centimetres (Laplace's Law).…”

“…La structure de la media est semblable dans beaucoup de primates, ce qui fait penser que cette espece d'animaux pourrait etre utile pour I'etude des aspects mecaniques de I'atherogenese. Wolinsky & Glasgov (1967) have described a lamellar unit structure for the arterial wall of mammals.…”