capillaries
Capillary: A tiny blood vessel where substances are exchanged between the blood and the body cells.
veins
The exchange of gases occurs at the ends of the airways in the lungs. Here tiny sacs called alveoli connect with tiny blood vessels and here exhaust gas [carbon dioxide] is exchanged for fresh gas [oxygen].
The human circulatory system consists of arteries, veins, and capillaries. The capillaries are the thin-walled vessels that connect arteries and veins and allow for the exchange of materials between blood and tissue fluid.
Gas exchange occurs in the vessels of the lungs
Capillaries
the blood vessel which allows gas exchange to occur is the capillaries
Capillaries via osmosis
Capillaries - The endometrium (epithelial lining/wall) of the capillaries is only one cell thick optimizing diffusion/osmosis between it and the tissue cells of the body
In hot weather - blood vessels dilate (widen) - to allow the exchange of heat between the blood and sweat glands. The sweat evaporates - cooling the blood.
Capillaries
Capillary system is where gas exchange occurs