Heart – 7% Aorta
Pulmonary circulation – 9% Systemic circulation – 84% and the accumulation of carbon dioxide and other tissue waste
products, and these in turn act directly on the local blood vessels, dilating or constricting them, to
control local blood flow precisely to that level required for the tissue activity. Also, nervous controlof
the circulation from the central nervous system and hormones provide additional help in controlling
tissue blood flow.
2. The cardiac output is controlled mainly by the sum of all the local tissue flows. When
blood flows through a tissue, it mediately returns by way of the veins to the heart. The heart responds
automatically to this increased inflow of blood by pumping it immediately back into the arteries. Thus,
the heart acts asan automaton, responding to the demands of the tissues. The heart, however, often
needs help in the form of special nerve signals to make it pump the required amounts of blood flow.
3. Arterial pressure regulation is generally independent of either local blood flow control or
