Gas exchange is the delivery of oxygen from the lungs to the bloodstream, and the elimination of carbon dioxide from the bloodstream to the lungs. It occurs in the lungs between the alveoli and a network of tiny blood vessels called capillaries, which are located in the walls of the alveoli.
Admitted for 180 days â Canadians admitted in âVisitor for Pleasureâ or B-2 status without a B-2 visa in hand are deemed to be admitted for 180 days under current US Customs and Border Protection (CBP) interpretation of the rules.
Whether youâll need a visa in Canada depends on the reason you're going. As a United States passport holder, you can visit Canada for tourism without a visa if you donât stay longer than 180 days. If you plan on any other activities during your stay, youâre likely to need a visa.