Figure 1

Aging produces a number of physical and biochemical changes in the vascular system that contribute to the age related degeneration of the brain. At the macroscopic level, reduced vessel density is observed in aging brains, leading to an overall reduced blood flow and oxygenation into brain tissue, that may be further exacerbated by pathological factors. At the cellular level, the vessel walls begin to reduce the expression of growth factor receptors, leading to reduced ability to respond to growth and survival factors. Vessels also begin to lose smooth muscle cells, reducing the capacity of vessels to maintain blood pressure, reducing oxygenation in certain circumstances. Aging also leads to a reduced expression of growth and survival factors into the bloodstream, further reducing the survival capacity of vessel lining cells. Many of these factors combine to lead to vessel degeneration, where reduced flow rates, reduced receptor expression and reduced growth factors lead to narrowing of vessels, further reducing flow and reducing vessel diameter, to a point where red blood cells can no longer flow through vessels, leading to loss of oxygenation of tissues and further degeneration into a string vessel state.