Relatively small amounts of blood are within the circulation (about 18%) and the (about 12%). the largest percentage of blood is within the systemic veins circulation (about 70%), with the greatest amount (about 55%) within the body's . the relatively large amount of blood within these vessels allows them to function as blood reservoirs. blood may be shifted from these reservoirs in times of physical exertion with . when less blood is needed at rest, it will be shifted back through by .

1) Pulmonary Circulation:This is the process where deoxygenated  blood is carried away from the right ventricle of the hearth while oxygenated blood is returned to the left ventricle and atrium of the heart.

 2) Heart: It is a muscular organ that pump blood through the blood vessels of the circulatory system.

3) Systemic vain: this is a vain that drain into the right right atrium 

4) Physical exertion:It the expenditure of energy expended during physical activity.

5) Vasoconstriction:It can be defined as the narrowing of the blood vessels which result into contraction of the muscular wall of the vessels most especially large arteries and small arterioles.

6) Vasodilation: This is when blood vessel is widening and result in relaxation of smooth muscle cell within the vessel walls.

an active site is a region that is present on an enzyme where the reactants or the substrate molecules we can say bind and experience a chemical reaction. the substrate is basically a reactant whose concentration is changing and that is converting into a product after binding at the active site of an enzyme