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      Pressure profile and morphology of the arteries along the giraffe limb.

      Journal of Comparative Physiology. B, Biochemical, Systemic, and Environmental Physiology

      Springer Nature America, Inc

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          Abstract

          Giraffes are the tallest animals on earth and the effects of gravity on their cardiovascular system have puzzled physiologists for centuries. The authors measured arterial and venous pressure in the foreleg of anesthetized giraffes, suspended in upright standing position, and determined the ratio between tunica media and lumen areas along the length of the femoral/tibial arteries in the hindleg. Volume fraction of elastin, density of vasa vasorum and innervations was estimated by stereology. Immunohistological staining with S100 was used to examine the innervation. The pressure increase in the artery and vein along the foreleg was not significantly different from what was expected on basis of gravity. The area of the arterial lumen in the hindleg decreased towards the hoof from 11.2 ± 4.2 to 0.6 ± 0.5 mm(2) (n = 10, P = 0.001), but most of this narrowing occurred within 2-4 cm immediately below the knee. This abrupt narrowing was associated with a marked increase in media to lumen area ratio (from 1.2 ± 0.5 to 7.8 ± 2.5; P = 0.001), and a decrease in mean volume fraction of elastin from 38 ± 6% proximal to the narrowing to 5.8 ± 1.1% distally (P = 0.001). The narrowing had a six-fold higher innervation density than the immediate distal and proximal regions. The sudden narrowing was also observed in the hind legs of neonates, indicating that it does not develop as an adaptation to the high transmural pressure in the standing giraffe. More likely it represents a preadaptation to the high pressures experienced by adult giraffes.

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          Most cited references 16

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          STRUCTURAL BASIS FOR THE STATIC MECHANICAL PROPERTIES OF THE AORTIC MEDIA.

           H Wolinsky,  S Glagov (1964)
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            Gravitational haemodynamics and oedema prevention in the giraffe.

            Because it is so tall, the giraffe, Giraffa camelopardalis, provides an important animal model for investigating adaptive mechanisms to orthostatic (gravitational) pressure changes. Previous physiological studies of the giraffe have concentrated on arterial blood pressures in the heart and neck. Briefly, these investigations revealed that arterial pressure near the giraffe heart is about twice that in humans, to provide more normal blood pressure and perfusion to the brain. Another important question is that of how giraffes avoid pooling of blood and tissue fluid (oedema) in dependent tissues of their extremities. As monitored by radiotelemetry, the blood and tissue fluid pressures that govern transcapillary exchange vary greatly with exercise. These pressures, combined with a tight skin layer, move fluid upward against gravity. Other mechanisms that prevent oedema include precapillary vasoconstriction and low permeability of capillaries to plasma proteins.
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              Small artery remodeling in hypertension.

               M J Mulvany (2002)
              Hypertension is associated with altered structure of the resistance vessels, a process known as remodeling. This review summarizes current concepts concerning the structure of a subgroup of the resistance vessels, the small arteries, and the modes of remodeling, some of the determinants of remodeling, and some signaling pathways for remodeling. It is shown that the available evidence points to important roles for blood flow and growth factors, in addition to blood pressure, as causes of resistance artery remodeling. Finally, the relationship between vascular structure and blood pressure is discussed, in particular with regard to the effects of antihypertensive therapy. Here again, it appears that blood flow plays an important role in allowing the correction of the abnormal resistance vessel structure seen in hypertension.
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                Author and article information

                Journal
                10.1007/s00360-010-0545-z
                21207038

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