Bronchi The trachea divides into two tubes called bronchi, one entering the left and one entering the right lung. Bronchi branch into smaller and smaller tubes known as bronchioles. Bronchioles terminate in grape-like sac clusters known as alveoli. Alveoli are surrounded by a network of thin-walled capillaries.
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The respiratory system can be divided into two parts: The upper respiratory tracts:mouth, nose & nasal cavity,pharynx and larynx The lower respiratory tracts:trachea,bronchi,bronchioles,alveoli,diaphragm
Bronchioles: Tertiary bronchi continue to divide and become bronchioles, very narrow tubes. There is no cartilage within the bronchioles and they lead to alveolar sacs.
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The Upper Respiratory Tracts
Mouth, nose & nasal cavity: The function of this part of the system is to warm, filter and moisten the incoming air.