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.
Visitors may stay for 90 days in the United States which also includes the time spent in Canada, Mexico, Bermuda, or the islands in the Caribbean if the arrival was through the United States. The Electronic System for Travel Authorization (ESTA) is not a visa.