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.
Under the old rules, permanent residents had to be living in Canada for three out of four years. Now, they must be physically present for at least 183 days per year in four of the six years before their application. In addition, permanent residents seeking citizenship must intend to continue to live in Canada.