Answer:
The exchange of substances between the blood vessels and the surrounding tissues can only happen in the capillaries.
Explanation:
Capillaries are the exchange vessels of our body. They form a network-like structure, called the capillary area. When blood, from the larger arterioles, spreads through the many capillaries in the capillary area, the blood pressure drops and the blood flows only at a slow speed. Through the thin, semi-permeable walls of the capillaries, the exchange of gas and substances between the blood and the surrounding tissue then takes place. Subsequently, blood continues to flow through the postcapillary venules, to which the capillary area has been reconnected. Blood pressure and blood flow increase and blood eventually reaches the heart through enlarged veins.
