Anatomy & Physiology

Anatomy & Physiology Study Guide

©2018 Achieve Page 297 22.3 Upper Respiratory System The nose is the primary passageway for air entering the respiratory system. Air normally enters through the paired external nares , or nostrils, which open into the nasal cavity. The nasal vestibule is the space contained within the flexible tissues of the nose. Coarse hairs in the epithelium of the vestibule extend across the external nares. Large airborne particles, such as sand, sawdust, or even insects, are trapped in these hairs and are thereby prevented from entering the nasal cavity. The nasal cavity is divided into left and right portions by the nasal septum. Hyaline cartilage forms the anterior portion of the nasal septum . This cartilaginous plate supports the dorsum nasi (bridge) and apex (tip) of the nose. The incoming air enters the nose and bounces off the conchal surfaces and churns like a stream flowing over rocks. This turbulence serves several purposes, for example, airborne particles swirl in the air and are likely to come into contact with the mucus coating the lining of the nasal cavity. Also, the turbulence provides time to modify incoming air for warming and humidifying, and it creates eddy currents that bring olfactory stimuli to the olfactory receptors. Portions of the maxillary and palatine bones form the floor of the nasal cavity and roof of the oral cavity, called the hard palate . A soft fleshy palate extends posterior to the hard palate, marking the boundary between the superior of 368 22.2 Organization of the Respiratory System The respiratory tract is made up of passageways that carry air to and from the exchange surfaces of the lungs. Anatomically, the respiratory system is divided into two regions: an upper respiratory system and a lower respiratory system. The upper respiratory system ends at the level of the vocal cords and consists of the nose, nasal cavity and accessory structures, and pharynx. These passageways protect the more delicate surfaces of, the lower respiratory system by filtering out particles, and humidifying and warming air. The lower respiratory system starts at the larynx (voice box) and moves through the trachea (windpipe), bronchi, bronchioles, and alveoli of the lungs. The air conduction portion begins at the entrance to the nasal cavity and extends through the respiratory tract to the bronchi and larger bronchioles. The respiratory part of the tract includes the smallest, most delicate bronchioles and the associated alveoli. These alveoli are air-filled pockets within the lungs where gas exchange occurs. The respiratory mucosa lines the conducting portion of the respiratory system. The lamina propria supports the respiratory epitheliumwith an underlying layer of areolar tissue. The delicate exchange surfaces of the respiratory system can be damaged if the inhaled air becomes contaminated with debris or pathogens. The respiratory defense system is a series of filtration mechanisms. Along much of the respiratory tract, mucous cells in the epithelium and mucous glands in the lamina propria produce sticky mucus that bathes exposed surfaces. In the nasal cavity, cilia and mucus capture and sweep trapped debris or microorganisms toward the pharynx, where it will be swallowed and exposed to the acids and enzymes of the stomach. The cilia beat toward the pharynx, moving a carpet of mucus in that direction and cleaning the respiratory surfaces, in the lower respiratory system. This process is usually described as a mucus (or mucociliary ) escalator .