Respiratory Histology Histology > Cardiovascular and Respiratory > Cardiovascular and Respiratory RESPIRATORY HISTOLOGY Key structures of the respiratory system 2 Functional Divisions The conducting portion • Conducts air, and comprises: the nose, nasal cavity, pharynx, larynx, trachea, bronchi, and bronchioles. • No gas exchange occurs in these structures. • Terminal bronchiole terminates the conducting portion of the respiratory tract. The respiratory portion • Site of gas exchange, and comprises: the respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli. Nose • Opens the respiratory system to the outside environment. Nasal cavity • Its mucosal lining moistens, warms, and cleans the inhaled air. Pharynx • Muscular tube that lies behind the nasal cavity, oral cavity, and larynx; it is open to them, and acts a conduit for air and food/liquid. Thus, it serves both the respiratory and digestive systems. Esophagus • Continues posteriorly to carry food to the stomach. Larynx • The cartilaginous structure that prevents food and liquid from entering the lower respiratory tract, and produces and modifies sounds (and is often referred to as the "voice box"). 1 / 4 Tracheobronchial tree • Collective term for trachea and its bronchial branches. Trachea (the "windpipe") • Descends through the neck to the thorax, and comprises C-shaped (vertically-stacked) cartilaginous rings. Primary Bronchi • First divisions of tracheobronchial tree • Aka, main bronchi Secondary bronchi • Serve lobes of the lungs • Aka, lobar bronchi Tertiary bronchi • Serve lung segments, called bronchopulmonary segments. • Aka, segmental bronchi With each successive division, the branches get narrower and the walls of the branches get thinner. Bronchioles • Terminal bronchioles are last portion of conducting division. Respiratory bronchioles • Beginning of respiratory division Alveolar sacs • Comprise small out pockets called alveoli, which have specialized walls to facilitate gas exchange with surrounding pulmonary capillaries. • The hundreds of millions of alveoli within give the lungs a light, spongy texture. 2 / 4 Lungs • Right lung comprises three lobes (divisions) and the left lung has only two lobes. • The heart nestles into the medial aspect of the left lung, which makes it slightly smaller than the right. HISTOLOGICAL FEATURES Tracheal ring • Comprises thick layer of purple-staining hyaline cartilage, which is covered by perichondrium on both sides. • Lamina propria and submucosa; though not visible in our sample, the submucosa contains seromucous glands and blood vessels. • Mucosal folds, which are lined with pseudostratified epithelia. Bronchi • Lumen is surrounded by mucosal pseudostratified epithelium. • Submucosal glands • Bundles of smooth muscle • Large plates of hyaline cartilage distinguish the larger bronchi. Smaller tertiary bronchi • Characterized by highly fractured and thin pieces of hyaline cartilage. Respiratory bronchioles • Thinner walls that lack cartilage and comprise simple cuboidal epithelial cells. • Alveolar outpockets arises directly from the respiratory bronchioles. • Club cells (formerly known as Clara cells), are cuboidal, non-ciliated cells in the bronchioles that secrete proteins. • Respiratory bronchiole gives rise to the alveolar ducts, which open to alveolar sacs. Alveoli • Type I pneumocytes (aka, alveolar cells), which are squamous epithelial cells. - Type I cells provide a thin surface for easy gas exchange with nearby pulmonary capillaries, which we can identify by the presence of red blood cells in their lumens. • Type II pneumocytes, which are rounder and bulge into the alveolus. 3 / 4 - Type II cells produce and secrete surfactant, which reduces surface tension and prevents alveolar collapse in exhalation; they also maintain and repair the alveolar wall. - Alveolar macrophages, aka, dust cells, fibroblasts, and mast cells are also present. Clinical Correlation Asthmatic airway: • Prolific goblet cells, lumen-obstructing mucus, and thickened basement membrane. - Allergic asthma is caused by hypersensitivity to allergens that trigger inflammatory responses, including mucus over- production, in the lungs and obstruct air flow. - Non-allergic asthma, on the other hand, is caused by pathological neural regulation of bronchiole diameter, and, therefore, air flow. Images: Histology (Mark Braun, MD, & Indiana University: http://medsci.indiana.edu/c602web/602/c602web/toc.htm; http://www.indiana.edu/~anat215/virtualscope2/start.htm) Powered by TCPDF (www.tcpdf.org) 4 / 4.