Autoregulation of blood flow and vascular resistance as mean arterial pressure is altered. The safe range for blood flow is about 80 to 125% of normal and usually occurs at arterial pressures of 60 to 160 mm Hg due to active adjustments of vascular resistance. At pressures above about 160 mm Hg, vascular resistance decreases because the pressure forces dilation to occur, at pressures below 60 mm Hg, the vessels are fully dilated, and resistance cannot be appreciably decreased further.
eventually leading to rupture of small vessels and excess fluid filtration into the tissue and edema.
Although the various mechanisms responsible for autoregulation are constantly interacting with the sympathetic nervous system, the actions of the sympathetic nervous system usually prevail in most organs. Only the cerebral and cardiac vasculatures exhibit impressive au-toregulatory abilities because the sympathetic nervous system is incapable of causing large increases in resistance in the brain and heart. Sympathetic dominance of vascular control in the majority of organ systems is beneficial to the body as a whole. Maintenance of the arterial pressure by sustained constriction of most peripheral vascular beds and perfusion of the heart and brain at the expense of the other organs that can tolerate reduced blood flow for prolonged periods of time is lifesaving in an emergency.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.