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.
In most cases, a valid U.S. or Canadian passport is sufficient documentation to allow for crossing the border. In other instances, such as when a Canadian citizen is hoping to immigrate to the U.S., a Visa is required. Nonetheless, Canadians can stay in the U.S. for an extended period of time without a Visa. How Long Can a Canadian Citizen Stay in the U.S. With Just a Passport? A Canadian citizen may visit the U.S. for up to six months within a 12 month period without a Visa. This means that the Canadian may enter the U.S. for business or pleasure for a total of six months without needing any documentation other than a passport.