The veins and arteries of many mammals facilitate the efficient transport of blood due to their elastic walls and cylindrical design

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"In a typical mammal body, the cylindrical arteries and veins which carry the blood have walls, containing the elastic fibre elastin, which expand to accommodate the spurts of blood pumped by the heart and then shrink again, pushing the blood onwards. The heart alone could never propel the blood all the way round the body if the blood vessels had rigid walls -- the blood would be stopping and starting all the time, instead of flowing. Strokes occur when the elasticity is lost." (Foy and Oxford Scientific Films 1982:23)

"The aortic wall of all vertebrates except agnathans contains a rubbery protein called elastin that allows the vessel to expand under the high pressures associated with cardiac contraction. In expanding, energy from the blood is temporarily stored in the elastin as elastic energy, but is promptly returned to the blood when the elastin recoils in diastole. This recoil acts as a second pump, forcing the blood on downstream and smoothing out pressure fluctuations. The total work of the heart is reduced as long as the transfer of energy into and out of the elastin is efficient. Elastin achieves both efficiency and long-range deformation with a high molecular mobility, although it is not clear how this mobility is achieved. Covalent crosslinks that unite individual molecules in an insoluble extracellular network ultimately limit this mobility and so allow the network to return to its original dimensions without permanent strain. Both high molecular mobility and insolubility are unusual for a protein, but they are understood to be necessary for elastomeric performance." (Chalmers et al. 1999:301)

The grand design: Form and colour in animalsJanuary 28, 1983
Sally Foy

Journal article
The hydrophobicity of vertebrate elastinsJournal of Experimental BiologyFebruary 28, 1999
Chalmers, G. W. G.; Gosline, J. M.; Lillie, M. A.

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