The pumps blood into the conducting arteries, which give off branches to supply the vital tissues of the body.Blood continuous to flow in the muscular arteries into the smallest arteries, called , which lead into the capillaries.The lumen of the capillaries is roughly equal to the diameter of . The thin wall is composed of . The function of capillaries is to materials between blood and tissue cells, such as the respiratory gases and The removal of waste products out of the cell prevents the accumulation of toxic substances.

Some tissues do not always require a high supply of nutrients, therefore, blood flow into capillaries is regulated by Metabolically active tissues have an capillary network and require an abundant supply of oxygen.Connective tissue has a low supply of oxygen while muscles, liver, and kidneys have a supply of oxygen.The of the skin completely a capillary network, so does the of the eye.

Blood continuous to flow from the capillaries into the , which lead into larger veins.Venous blood is returned to the right atrium of the heart by the and the

1) What is the direction of net flow at the arteriolar end of the capillaries? Explain why.

2) What is the direction of net flow at the venous end of the capillaries? Explain why.

3) The rate of diffusion is determined by Fick’s law. Explain how diffusion and the exchange of gases across the capillary wall is affected by different factors in Fick’s law.

4) Small organisms have a high metabolism in order to maintain their body temperature, as they readily lose heat. Explain why large organisms are able to maintain their body temperature, although they have a low metabolism.