Anat. & Phys. Study Guide: Exam #2 Chapter 22- The Respiratory System ° The respiratory system: Upper respiratory tract- structures in the head and neck; nose, pharynx, larynx Lower respiratory tract- structures in the thorax; trachea, bronchi, lungs Conducting division- airflow only; nose to main bronchi Respiratory division- gas exchange; respiratory bronchioles and alveoli ° ° The structures of the bronchiole and alveoli: Bronchioles- continuations of the airway that lack supportive cartilage and are 1 mm or less in diameter o Pulmonary lobule- portion of the lung ventilated by one bronchiole o Ciliated cuboidal epithelium and well developed smooth muscle in the walls o Terminal bronchiole- the division of bronchioles into 50 to 80 branches; the final branches of the conducting system Less than 0.5 mm in diameter Ciliated No mucous glands of goblet cells Respiratory bronchioles- two or more smaller branches of the terminal bronchiole; have alveoli budding from their walls Smallest and nonciliated Alveolar ducts- elongated, thin-walled passages divided from respiratory bronchioles; alveoli along walls Alveolar sacs- the ending of the alveolar ducts; grapelike clusters of alveoli arrayed around a central space called the atrium Alveoli/ alveolus- pouch about 0.2-0.5 mm in diameter o Squamous (type I) alveolar cells- thin, broad cells, covering about 95% of the alveolar surface area
Thinness allows for rapid gas diffusion between air and blood Minimal barrier to gas exchange (respiratory membrane) o Great (type II) alveolar cells- cells covering 5% of the alveolar surface area; more numerous Secrete pulmonary surfactant (mixture of phospholipids and protein that coats the alveoli and smallest bronchioles and prevent them from collapsing when one exhales) Repair the alveolar epithelium when the squamous cells are damaged. o Alveolar macrophages- most numerous cells in the lung, wander the lumens of the alveoli and the connective tissue between them Keep the alveoli free of debris by phagocytizing dust particles that escape entrapment by mucous in the higher parts of the respiratory tracts o Respiratory membrane- the barrier between the alveolar air and blood; consists only of the squamous alveolar cell ° ° Inspiration and expiration (pulmonary ventilation): Inspiration- inhaling o Increase in volume and lower pressure in the thoracic cavity; air flows down pressure gradient Expiration- exhaling o Reduce volume and raise pressure in the thoracic cavity; air flows out Respiratory cycle- one complete breath Quiet respiration- relaxed, unconscious, automatic breathing Forced respiration- unusually deep or rapid breathing Muscles the ventilate lungs: Principal muscles- diaphragm and intercostal muscles Prime mover- diaphragm
o Contracts- tenses and flattens, dropping, enlarging thoracic cavity and pushing outward on the sternum, and ribs further enlarging thoracic cavity (inhalation) Synergist- internal (forced expiration) and external intercostals (inspiration) o
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