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Respiratory Epithelium, Larynx and Trachea LEARNING OBJECTIVES At the end of the lecture the student shouldbe able to know : • Different layers of larynx • Histological characteristics of each layer of larynx • Histological classification of laryngeal cartilage • Structure of trachea and its layer • Different layers of trachea and their histological characteristics LECTURE OUTLINE The respiratory system includes the lungs and a system of tubes that links the sites of gas exchange with the external environment. A ventilation mechanism, Respiratory System Consists of Lungs and Respiratory Passages. Conducting portion Respiratory portion Functions of Respiratory Epithelium Exchange of O2 and CO2 between the blood and inhaled air across the alveoli Olfaction Phonation Conducting Portion Respiratory Portion Respiratory Epithelium Following types of epithelia line the respiratory system: Ciliated Pseudo stratified Columnar epithelium-conducting portion up to the large bronchioles. Ciliated Simple cuboidal epithelium-terminal bronchioles Simple squamous epithelium-alveoli. Bronchial Wall Constituents Cilia Goblet cells Glands Cartilage Smooth muscle fibers Elastic fibers Cell Types Electron microscopy reveals Six types of cells present in epithelia lining the conducting portion. Ciliated columnar cells Goblet cells Brush cells Basal (short) cells Small granular cells Clara cells LARYNX The respiratory system is composed of two main parts: 1. A system of progressively smaller, structurally and functionally complex tube known as airway. 2. A respiratory unit at the distal end of airway, where gases are exchanged between the airway and circulating blood. Airway (conducting part) It starts from nasal cavity, continues in the nasopharynx, larynx, trachea, bronchi, bronchioles and terminal bronchioles. Its function is to clean, moisten and warm the inhaled air and conduct it to respiratory part. Respiratory unit Here exchange of gases takes place. It is composed of respiratory pulmonary alveoli bronchioles, alveolar ducts, alveolar sacs and Trachea divides into two primary (main) bronchi which enter in the substance of lung. They are also accompanied by pulmonary vessels and bronchial vessels. The primary bronchi subdivide within lung into secondary or lobar bronchi. The lobar bronchi divide into tertiary or segmental bronchi which are 10 in right lung and 8 in the left. Segmental bronchi go on dividing until they become 1mm in diameter, now known as bronchioles. Bronchioles continue to divide and when they have reduced to 0.5 mm they are known as terminal bronchioles LARYNX An irregular tube that connects pharynx to the trachea. Laryngeal wall consists of: Mucosa Cartilages Intrinsic muscles LARYNGEAL MUCOSA Comprises of: Epithelium Lamina propria Mucosa forms 2 pairs of folds Upper pair constitutes false vocal cords (vestibular folds) Lower pair constitutes true vocal cords. Epithelium Varies in type in different parts of the larynx: Stratified squamous noncornified epithelium Laryngeal inlet Most of the epiglottis True vocal cords Typical respiratory epithelium covers the rest of the larynx. Lamina propria Consists of fine connective tissue and contains TRUE VOCAL CORDS FALSE VOCAL CORDS LARYNGEAL CARTILAGES Unpaired Cartilages:Epiglottis Thyroid. Cricoid Paired Cartilages:Arytenoids. Thyroid. Cricoid HISTOLOGICAL CLASSIFICATION OF LARYNGEAL CARTILAGES Hyaline Cartilages Thyroid Cricoid Most of arytenoids Subject to calcified in old age. 1.2.3.- ELASTIC CARTILAGES OF LARYNX Epiglottis Cuneiforms, Corniculates Tips of arytenoids EPIGLOTTIS Unpaired cartilage Elastic; covered on both side by mucosa comprising of epithelium and lamina propria. EPITHELIUM OF EPIGLOTTIS Anterior (lingual) surface and upper part of posterior (laryngeal) surface are covered by stratified squamous noncornified epithelium. Lower half of the posterior surface is covered by the respiratory epithelium. EPIGLOTTIS LAMINA PROPRIA Contains tubulo-alveolar glands of mixed type. mainly on the posterior surface Scattered taste buds are present between the epithelial cells on the posterior surface TRACHEA Thin wall tube, about 10 cm long, Extends from the base of larynx to sternal angle Bifurcates in to two primary bronchi. HISTOLOGY OF TRACHEA Consists of Mucosa Epithelium Lamina propria submucosa Adventitia MUCOSA OF TRACHEA Made up of epithelium and lamina propria Epithelium Respiratory with numerous goblet cells. TRACHEA LAMINA PROPRIA 16-20 C-shaped rings of hyaline cartilage SUBMUCOSA Consists of loose Connective tissue Contains numerous tubulo-alveolar glands that open on to the mucosal surface ADVENTITIA Mainly composed of loosely arranged collagenous fibers Lodges small blood vessels and autonomic nerve, which supply trachea