Respiratory problems

The walls of the airway produce mucus that keeps air moist and warm. The surface of the walls is lined with tiny hairs, which move rather like fields of wheat. They help to move dust and foreign bodies away from the lungs to be coughed up or sneezed out of the airway If particles are not removed—as in the case of smokers, in whom the hairs become paralyzed by nicotine—they remain in the lung. This encourages viruses and bacteria to create infection, and excessive amounts of mucus to be produced. Small airways and alveoli (see right) may become flooded with mucus, with the result that respiration deteriorates, and gas exchange fails. This occurs in pneumonia. Certain irritants may cause spasms of the airway, as in asthma.

Mucous membranes in nasal cavity trap foreign bodies in inhaled air

Upper pharynx allows passage of air; lower pharynx, air, foods, and fluids

Larynx separates pharynx from trachea, or windpipe

Primary bronchi branch into ever-smaller airways (see diagram, below)

Trachea divides into two primary bronchi, one serving each lung

Lungs are enclosed by thin membranes called pleurae

Diaphragm separates chest cavity from abdominal cavity

Mucous membranes in nasal cavity trap foreign bodies in inhaled air

Lungs are enclosed by thin membranes called pleurae

Abdominal muscles assist with expansion and contraction of chest cavity during breathing the respiratory tract Air is taken in through the nose and mouth, and filtered and purified in the upper respiratory tract— the airway extending as far as the trachea. Air continues down the lower respiratory tract, which begins where the larynx meets the trachea and extends deep into the lungs by means of an extensive network of bronchial airways.

Abdominal muscles assist with expansion and contraction of chest cavity during breathing

Heart pumps blood to lungs through pulmonary arteries

Alveolus Bronchiole where gases are exchanged The lungs' branching bronchi feed into tiny respiratory bronchioles and ultimately the alveoli, small balloonlike sacs. Oxygen diffuses through the walls of the alveoli into a network of capillaries, and then into the bloodstream. Carbon dioxide diffuses from the blood vessels into the alveoli to be exhaled from the lungs.

Alveolus Bronchiole

Bronchus

Bronchus

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