In a closed circulatory system, transfers between blood and the cells of other tissues take place across ____.

A) capillaries
B) veins
C) arteries
D) lymph vessels
E) all blood vessels

Capillaries are the smallest blood vessels in the circulatory system and are responsible for the exchange of substances between the blood and the cells of other tissues. They have thin walls that allow for the diffusion of gases, nutrients, and waste products between the blood and surrounding tissues. Veins and arteries, on the other hand, are larger blood vessels that mainly transport blood to and from the heart, but do not facilitate the exchange of substances with tissues to the same extent as capillaries. Lymph vessels are a part of the lymphatic system, which is responsible for immune function and the drainage of excess fluid from tissues, and are not directly involved in the transfer between blood and other tissues.