Blood flows rapidly within the arterial system but slows dramatically as it enters the capillaries. What is the benefit of having blood move slowly through the capillaries?

Question

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The slow movement of blood through capillaries allows enough time for the exchange of materials with surrounding cells. Capillaries are the site of nutrient and gas exchange between the blood and body tissues. The slow flow rate allows sufficient time for oxygen and nutrients to diffuse from the blood into the surrounding tissues, while waste products (such as carbon dioxide) diffuse from the tissues into the blood. This process is facilitated by the thin walls of the capillaries and the slow movement of blood through them.

Blood Flows Rapidly Within the Arterial System but Slows Dramatically