Lower Respiratory Tract: Parts and Functions Trachea: The trachea, or windpipe, is the passage through which air enters or leaves the lungs. It extends downward from the base of the larynx and lies in between the neck and chest cavity . The trachea is strengthened with rings of cartilage so that air can flow easily before reaching the lungs. It is also lined with cilia to remove any foreign material from the airway and to further warm and moisten the air. At the bottom, the trachea divides into two bronchi tubes that join the lungs.
Lungs : Within the lungs, the bronchi divide into left and right bronchi, which further branch into bronchioles. Bronchioles are extremely thin and carry oxygen deeper into the lungs. At the end of bronchioles, tiny air sacs called alveoli transfer oxygen and absorb carbon dioxide from the blood.
Superior vena cava
Carbon dioxide leaves veins
Oxygen enters alveoli
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