The circulatory system consists of the heart pumping blood to the rest of the body. This is to provide oxygen to the tissues in order for them to function. One of the circulation theories of the body is that blood flow to the tissue is almost always controlled in realation to tissue needs. This is because the heart cannot send blood everywhere at the same time at the same rate. There are times when there's low oxygen or increasing dilating metabolic products in certain tissues compared to the rest of the body. The blood would therefore flow at an increased rate to that affected area.
Comments
comment
This paragraph is very concise and clear. For the fourth sentence in you could even reword it structurally and say, " In certain circumstances when the body is low in oxygen or there is an increase in dilated metabolic patterns .... blood flow rate would increase in that area."
Comment III
Avoid use of "one of "
Theory elaboration
It sounds as if there are other theories that could be expanded upon or discussed.