Nervous Tissue

Nasopharynx (nay-zoh-FAIR-inks): The superior part of the pharynx located behind the nasal cavity; its lining is primarily respiratory epithelium (pseudostratified ciliated columnar) because it functions exclusively for air conduction. Oropharynx (or-oh-FAIR-inks): The middle part of the pharynx located behind the oral cavity; its lining is non-keratinized stratified squamous epithelium because it is a common passageway for both food and air, requiring protection from abrasion. Epiglottis (ep-ih-GLAH-tis): A leaf-shaped flap of cartilage (mostly elastic cartilage) covered by stratified squamous epithelium on its lingual surface and respiratory epithelium on its laryngeal surface; its function is to cover the opening of the larynx during swallowing to prevent aspiration of food. Laryngopharynx (luh-ring-goh-FAIR-inks): The inferior part of the pharynx located posterior to the larynx; it is lined by non-keratinized stratified squamous epithelium and connects the oropharynx to the esophagus. Larynx (LAIR-inks): The voice box, a short, rigid tube made primarily of thyroid cartilage, cricoid, and arytenoid cartilages; it connects the laryngopharynx to the trachea and functions in phonation (voice production) and regulating air flow. Trachea (TRAY-kee-uh): A rigid tube that extends from the larynx to the primary bronchi; it is supported by 16-20 C-shaped rings of tracheal (hyaline) cartilage and is lined by respiratory epithelium for filtering and humidifying air. Thyroid cartilage (THY-royd KAR-tuh-lij): The largest cartilage of the larynx (forms the "Adam's apple"); it is composed of hyaline cartilage and protects the vocal cords. Primary bronchi (PRY-mer-ee BRON-ky): The two main branches that split from the trachea; they enter the root of each lung and structurally resemble the trachea, containing C-shaped cartilage rings and respiratory epithelium. Trachealis muscle (tray-kee-AY-lis MUS-ul): A band of smooth muscle that bridges the gap between the open ends of the C-shaped rings of tracheal (hyaline) cartilage) on the posterior side of the trachea; its contraction reduces the diameter of the trachea during coughing. Respiratory epithelium (Pseudostratified ciliated columnar epithelium) (RES-puh-ruh-tor-ee ep-uh-THEE-lee-um/SOO-doh-STRAT-uh-fyde SIL-ee-ay-tid KOL-um-nar ep-uh-THEE-lee-um): The characteristic epithelial lining of the large conducting airways (nasopharynx, larynx, trachea, and bronchi); it consists of ciliated cells, goblet cells, and basal cells, forming the mucociliary escalator. Basal cell (BAY-sul sell): Small, low-lying cells that rest on the basement membrane of the respiratory epithelium but do not reach the lumen; they act as stem cells to regenerate the ciliated and goblet cells. Ciliated cell (SIL-ee-ay-tid sell): The most numerous cell type in the respiratory epithelium; they possess numerous apical cilia whose coordinated beating sweeps mucus (from the goblet cells) and trapped particles toward the pharynx for swallowing. Goblet cell (GAH-blut sell): Mucus-secreting epithelial cells found interspersed among the ciliated cells in the respiratory epithelium; they produce mucus that traps inhaled dust and pathogens. Tracheal (hyaline) cartilage (TRAY-kee-ul HY-uh-lin KAR-tuh-lij): The supporting C-shaped rings of hyaline cartilage found in the wall of the trachea; they prevent the airway from collapsing during inspiration. Adventitia (ad-ven-TISH-uh): The outermost layer of loose connective tissue that surrounds the trachea and large bronchi; it blends with the surrounding connective tissue and contains large blood vessels and nerves. Seromucous acinus (sir-oh-MYOO-kus AS-ih-nus): The secretory unit of mixed glands found in the submucosa of the trachea and bronchi; these glands produce both watery (serous) and viscous (mucous) secretions that help humidify the air and contribute to the mucus layer. Secondary (lobular) bronchus (SEK-un-der-ee LAH-byoo-ler BRON-kus): The large branches of the primary bronchus that supply the lobes of the lung (three on the right, two on the left); their walls contain irregular cartilage plates rather than C-rings. Tertiary (segmental) bronchus (TUR-shee-er-ee seg-MEN-tul BRON-kus): The smaller branches of the secondary bronchus that supply the bronchopulmonary segments of the lung; they possess smaller, sparser cartilage plates and are the last conducting structures to contain cartilage. Bronchiole (BRON-kee-ohl): A small conducting airway (less than 1 mm in diameter) that lacks cartilage plates and submucosal glands; its wall is primarily composed of smooth muscle, which regulates air flow. Terminal bronchiole (TUR-mih-nul BRON-kee-ohl): The last segment of the purely conducting airway, branching into respiratory bronchioles; its epithelial lining transitions from ciliated columnar to cuboidal and is characterized by the presence of Club cells (Clara cells). Respiratory bronchiole (RES-puh-ruh-tor-ee BRON-kee-ohl): The first segment of the airway capable of gas exchange; its wall is partially lined by cuboidal epithelium (Club cells) interspersed with small outpockets of alveoli. Alveoli (singular: alveolus) (al-VEE-uh-ly/al-VEE-uh-lus) The numerous tiny, cup-shaped sacs that constitute the terminal unit of the respiratory system; they are lined by simple squamous epithelium and are the primary site of gas exchange. Club cell (klub sell): Non-ciliated, dome-shaped epithelial cells found in the bronchioles (especially terminal and respiratory); they secrete a lipoprotein that prevents the bronchiolar walls from sticking together and can detoxify airborne substances. Alveolar air space (al-VEE-uh-ler air spays): The lumen or interior space of the alveoli; this space is separated from the surrounding blood capillaries only by the extremely thin fused basement membrane and the type 1 pneumocytes, facilitating gas exchange. Type 1 pneumocyte (Squamous alveolar cell) (type wun NOO-muh-syt): Extremely thin, flat simple squamous epithelial cells that cover about 95% of the alveolar air space surface; their thinness is essential for the efficient diffusion of gases (oxygen and carbon dioxide). Type 2 pneumocyte (Great alveolar cell) (type too NOO-muh-syt): Rounded or cuboidal epithelial cells scattered among the type 1 pneumocytes; they are responsible for secreting pulmonary surfactant, a lipoprotein that reduces surface tension in the alveoli and prevents collapse. Alveolar macrophage (Dust cell) (al-VEE-uh-ler MAK-roh-fayj): Phagocytic immune cells found migrating within the walls and across the surface of the alveoli; their primary function is to engulf particulate matter (dust) and pathogens that reach the lower respiratory tract. Fused basement membrane (fyoozd BAYS-munt MEM-brayn): A single, very thin basement membrane formed by the fusion of the basement membrane of the type 1 pneumocyte and the basement membrane of the adjacent capillary endothelial cell; this forms the central layer of the blood-air barrier to maximize gas exchange efficiency.