10. Histology of the Respiratory System .pdf

HISTOLOGY OF RESPIRATORY SYSTEM STRUCTURE ASSOCIATED LAB/LECTURE PHOTO TRACHEA: Mucous membrane: - It is lined by pseudostratified ciliated columnar epithelium with goblet cells resting on a basement membrane. - Deep to the basement membrane...

HISTOLOGY OF RESPIRATORY SYSTEM STRUCTURE ASSOCIATED LAB/LECTURE PHOTO TRACHEA: Mucous membrane: - It is lined by pseudostratified ciliated columnar epithelium with goblet cells resting on a basement membrane. - Deep to the basement membrane is the lamina propria made up of areolar tissue with elastic fibres and lymphocytes. Submucosa - It is composed of a loose meshwork of connective tissue, containing large blood vessels and nerves. - Mucous, serous and mixed types of glands also occur in this layer. - Their ducts open on the free surface of the epithelium. Hyaline Cartilage - It is present outside the submucosa. - Cartilage is covered by perichondrium on all sides, which separates it from the neighbouring structures. - Cartilages are enclosed in an elastic fibrous membrane, which connects the cartilages to one another. - Posterior wall of trachea is devoid of cartilage. - Here outer longitudinal and inner circular layers of smooth muscles (trachialis muscle) are present within the fibrous membrane. Adventitia - It is the outer most layer with connective tissue, blood vessels and nerves. LUNG A section through the lung shows the cut sections of - Bronchi - Bronchioles - Alveoli - Branches of pulmonary artery - Tributaries of pulmonary vein Bronchi a. Mucosa - It is consisting of pseudostratified ciliated columnar epithelium. - It is highly folded because of underlying smooth muscle fibers. b. Lamina Propria - Contains connective tissue, smooth muscle fibers and mucous and serous glands c. Hyaline Cartilage - Is seen outside lamina propria and found in small pieces. Bronchiole a. Mucosa - It is made up of simple columnar cells with folds. b. Lamina Propria - Contains some connective tissue and smooth muscle fibers, which are responsible for the folds of mucous membrane. - Glands and cartilages are absent. Alveoli - Are lined by simple squamous cells. - Between the alveoli there is very thin interalveolar septa with capillaries, elastic fibers and various types of cells like fibroblasts, mesenchymal cells, macrophages etc. - The lining cells of alveoli are of 2 types. a. Squamous (type 1) cells - There are simple squamous cells. - They have prominent nuclei projecting into lumen. b. Secretory (type 2) cells - These are rounded cells that project into the lumen. - The secretions of these cover the inner surface of the alveoli and act as a  surfactant, which reduces the surface tension of the alveoli and prevents the collapse of alveoli during expiration. - there are alveolar phagocytes (dust cells) seen bulging from the walls of alveoli into the lumen. Blood Vessels - Cut sections of branches of pulmonary artery and tributaries of pulmonary veins are seen close to the bronchi. - They are lined by simple squamous epithelium.