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.
Tourist Cards for Canadian citizens are valid for 90 days, but can be extended in the same manner as those for foreign nationals for a maximum stay of 6 months. Travelers must have travel insurance which covers medical expenses or a policy for medical expenses with coverage in Cuba.