Comparison of Abdominal and Thoracic Aortic Medial Structure in Mammals

Previous studies of adult mammalian thoracic aortas revealed that tension per medial lamellar unit was independent of species and that distribution of medial vasa vasorum, number of medial lamellar units and medial thickness were consistently related. Except for man, a similar pattern prevailed in abdominal aortic segments of all of the ten species studied. The human abdominal aortic media had relatively fewer lamellar units for its diameter than abdominal or thoracic aortas of other species, resulting in a relatively elevated estimated mean tension per lamellar unit. Vasa were normally absent from the human abdominal aortic media, even though its thickness significantly exceeded the thickness of avascular medias of other species and of avascular zones of medias with vasa vasorum. Elevated calculated tension per lamellar unit and excessive avascular thickness may be factors in the increased susceptibility of human abdominal aortas to atherosclerosis.