Respiratory system Complete Study Guide_ Guaranteed Success.

In mammals, a system of branching ducts conveys air to the lungs, which are located in the thoracic cavity. • Air enters through the nostrils and is then filtered by hairs, warmed, humidified, and sampled for odors as it flows through a maze of spaces in the nasal cavity. • The nasal cavity leads to the pharynx, an intersection where the paths for air and food cross. When food is swallowed, the larynx (the upper part of the respiratory tract) moves upward and tips the epiglottis over the glottis (the opening of the trachea, or windpipe). This allows food to go down the esophagus to the stomach. The rest of the time, the glottis is open, enabling breathing. • From the larynx, air passes into the trachea. Cartilage reinforcing the walls of both the larynx and the trachea keeps this part of the airway open. The trachea wall contains a series of cartilage ¾ rings which prevent the trachea wall from collapsing, thus maintaining an open passageway for air. o Within the larynx of most mammals, exhaled air rushes by a pair of elastic bands of muscle called vocal cords. Sounds are produced when muscles in the larynx are tensed, stretching the cords so they vibrate. High-pitched sounds result from tightly stretched cords vibrating rapidly low-pitched sounds come from less tense cords vibrating slowly. • The trachea branches into two bronchi (singular, bronchus), one leading to each lung. • Within the lung, the bronchi branch repeatedly into finer and finer tubes called bronchioles. - The entire system of air ducts has the appearance of an inverted tree, the trunk being the trachea. The epithelium lining the major branches of this respiratory tree is covered by cilia and a thin film of mucus. o The mucus traps dust, pollen, and other particulate contaminants, and the beating cilia move the mucus upward to the pharynx, where it can be swallowed into the esophagus. This process, sometimes referred to as the “mucus escalator,” plays a crucial role in cleansing the respiratory system. 2 | P a g e - Gas exchange in mammals occurs in alveoli (singular, alveolus), air sacs clustered at the tips of the tiniest bronchioles. - Human lungs contain millions of alveoli, which together have a surface area of about 100 m2 , 50 times that of the skin. • Oxygen in the air entering the alveoli dissolves in the moist film lining their inner surfaces and rapidly diffuses across the epithelium into a web of capillaries that surrounds each alveolus. • Net diffusion of carbon dioxide occurs in the opposite direction, from the capillaries across the epithelium of the alveolus and into the air space. - Lacking cilia or significant air currents to remove particles from their surface, alveoli are highly susceptible to contamination. White blood cells patrol alveoli, engulfing foreign particles. • However, if too much particulate matter reaches the alveoli, the defenses can be over