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In the alveoli Alveolus (also called air sac) is the capillary-rich sac in the lungs where the exchange of oxygen and carbon dioxide takes place by diffusion.
Words to Know. Alveoli: Tiny air-filled sacs in the lungs where the exchange of oxygen and carbon dioxide occurs between the lungs and the bloodstream. Bronchi: Two main branches of the trachea leading into the lungs.Bronchial tree: Branching, air-conducting subdivisions of the bronchi in the lungs.he exchange of these gases occurs across cell membranes both in the lungs (external respiration) and in the body tissues (internal respiration). Breathing, or pulmonary ventilation, describes the process of inhaling and exhaling air. The human respiratory system consists of the respiratory tract and the lungs.