For this system, it is necessary to separate the aging effects on the cardiac muscle and its apparatus from the aging of the vessels of the circulatory system, which transports blood to and from the heart. A characteristic of aging is a diminished resting cardiac output, which can have the combined bases of lower force of the cardiac muscle and a lesser oxygen demand for metabolism with diminished active-cell mass. Aging of the myocardium reduces its capacity for cellular repair and replacement. With aging, elevations of noradrenaline (norepinephrine) associated with downregulation of beta-1 receptors mimics the process of the failing heart. The compliance of the arteries emanating from the heart decreases with age. Stiffening of these vessels produces a progressive rise in the systolic blood pressure.
It is the circulation through smaller blood vessels and the generation of new vessels (neovasculariza-tion) that is a major concern with advancing years. The process of angiogenesis, through which new blood vessels are formed, is impaired during aging. The integrity of endothelial cells lining the vessels, the cascade of coagulation factors, and growth factors and neurochemical mediators and their respective receptors are all altered by aging in the neovascular-ization processes.
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