Respiratory System II-1.pptx

Respiratory System II By : Rakhshindah Qureshi Learning Objectives : 1. Describe the morphology of the respiratory divisions of the respiratory system . 2.Describe the morphology and explain the functions of the major cell types found in the respiratory portion of the respiratory system . 3. Descr...

Respiratory System II By : Rakhshindah Qureshi Learning Objectives : 1. Describe the morphology of the respiratory divisions of the respiratory system . 2.Describe the morphology and explain the functions of the major cell types found in the respiratory portion of the respiratory system . 3. Describe the branching pattern of pulmonary vasculature . 4. Describe the histology of pleura . 5. Discuss the clinical correlates presented in the lecture . Reference : Color Atlas of Histology Gartner & Hiatt 7th edition Respiratory System • The respiratory system is responsible for respiration , thereby provides oxygen for use by the cells and eliminates carbon dioxide produced during cellular metabolism . • The respiratory system is divided into 2 functionally distinct portions : • 1. CONDUCTING PORTION : • Nasal cavity • Nasopharynx • Larynx • Trachea • Bronchi • Bronchioles • Terminal bronchioles • 2. RESPIRATORY PORTION : • Respiratory bronchioles • Alveolar ducts • Alveolar sacs and • Alveoli . Segmentation of the Intrapulmonary Bronchial Tree • Respiratory portion : • Is that part of the respiratory tract in which gas exchange occurs . • After entering the lung parenchyma , the bronchi divide into intrapulmonary secondary bronchi . • The right lung receives 3 intrapulmonary secondary bronchi • The left lung receives 2 intrapulmonary secondary bronchi . • Intrapulmonary secondary bronchi subdivide into segmental tertiary bronchi supplying each bronchopulmonary segment . • Blood vessels enter the lung with the bronchi .The arteries branch into smaller vessels as they follow the bronchial tree into the substance of the lung . Capillaries come into intimate with the terminal respiratory units ----- the alveoli .This intimate relationship between the alveolar space and the pulmonary capillaries is the basis of gas exchange within the lung parenchyma Pulmonary lobule and Pulmonary acinus • A terminal bronchiole and the associated region of pulmonary tissue that it supplies constitutes a pulmonary lobule . • A pulmonary lobule includes: • Terminal bronchiole • Respiratory bronchioles • Alveolar ducts • Alveolar sacs • Alveoli • Pulmonary acinus : physiologists designate as the portion supplied by respiratory bronchiole. • Each acinus includes : • Respiratory bronchiole • Alveolar duct • Alveolar sac • Alveoli Emphysema • Chronic obstructive pulmonary disease (COPD) is characterized by progressive and often irreversible airflow limitations e.g., emphysema and asthma . • COPD occurs in the bronchioles and lung parenchyma .Elastic fibers are an important component of bronchioles and lung parenchyma. A loss of elasticity and breakdown of elastic fibers gives rise to emphysema .As a result adjacent alveoli become confluent creating large air spaces or blebs . Histological characteristics of specific regions of the respiratory portion of respiratory system • Respiratory bronchioles: • The initial segment of the respiratory portion, arising immediately from the terminal bronchioles of the conducting portion • Structurally they are like terminal bronchiole except for the presence of a few alveoli projecting of their wall . Histological characteristics of specific regions of the respiratory portion of respiratory system • Respiratory bronchioles: • The epithelium of respiratory bronchioles is devoid of goblet cells , and largely consists of ciliated cuboidal cells and a smaller number of non-ciliated Clara cells . • Smooth muscle and elastic connective tissue comprise the lamina propria . • Bundles of smooth muscle bulge into the lumen of respiratory bronchioles . • Proceeding distally along the respiratory bronchioles , alveoli become more numerous . Histological characteristics of specific regions of the respiratory portion of respiratory system • Alveolar duct : simply a tube with alveoli completely making up its wall . • Alveolus : where the gas exchange between air and blood takes place . • Alveoli are sac like protrusions ~200μm in diameter extending from the wall of respiratory bronchiole, alveolar ducts and alveolar sacs . • The numerous alveoli are responsible for the sponginess of the lung . • Alveolar sac : a grouping or clump of alveoli that communicate with one another Histological characteristics of specific regions of the respiratory portion of respiratory system • Alveolus : • The alveolus is the functional unit of the pulmonary acinus . • About 200 million alveoli in each lung provide a total area of 75 m² for oxygen and carbon dioxide exchange . • Each alveolus has a thin wall with capillaries lined by simple squamous epithelial cells forming a part of air – blood barrier . Histological characteristics of specific regions of the respiratory portion of respiratory system • Alveolus histology : • The alveolar epithelium consists of two cells types : • Type 1 alveolar cells lining 90% of alveolar surface • Type II alveolar cells covering 10% of the alveolar surface area . • Additional cells are the macrophages ( dust cells) , fibroblasts and mast cells . Histological characteristics of specific regions of the respiratory portion of respiratory system • Alveolus histology : • Alveolar capillaries are lined by continuous endothelial cells juxtaposed to Type I alveolar cells through a dual basal lamina produced by these two cells . • Alveolar endothelial cells contain angiotensin – converting enzyme (ACE) for the conversion of angiotensin I to angiotensin II . Histological characteristics of specific regions of the respiratory portion of respiratory system • Alveolus histology : • A. TYPE I PNEUMOCYTES: • Simple squamous epithelial cells that make up ~ 90% of the alveolar surface . • Histology and Function : • These cells are extremely thin < Histological characteristics of specific regions of the respiratory portion of respiratory system • TYPE I PNEUMOCYTES : • Histology & Function : • Most of the organelles are grouped around the nucleus, and the thin rim of cytoplasm has many pinocytotic vesicles. These vesicles are involved with the: • a) removal of small contaminants and • b) turn over of surfactant . • Tight junctions join the cells thereby preventing leakage of body fluids into alveoli . Histological characteristics of specific regions of the respiratory portion of respiratory system • Alveolus histology : 2. TYPE II PNEUMOCYTES • (greater alveolar cells )are interspersed among type I pneumocytes comprising the other ~10% of the alveolar surface . • Are predominantly located at the angles formed by adjacent alveolar septa . • Histology : cuboidal cells with a domed apical surface. The type II cells are secretory cells hence abundance of rER & Golgi apparatus . Histological characteristics of specific regions of the respiratory portion of respiratory system • Alveolus histology : 2. TYPE II PNEUMOCYTES • Lamellar bodies : are the ultrastructural feature of type II cells .These distinctive membrane bound vesicles contain a series of layered lamellae composed of pulmonary surfactant . • Lamellar bodies represent cell's secretory granules . Histological characteristics of specific regions of the respiratory portion of respiratory system • FUNCTIONS OF TYPE II PNEUMOCYTES • A. Release of pulmonary surfactant • The primary constituent of surfactant is phospholipids (~85-90%) but surfactant specific proteins are also present . • Surfactant is released by exocytosis onto the lumenal surface of alveolar epithelium, where it form a thin film that reduces the surface tension at air epithelial interface. This is important in preventing collapse of alveoli during expiration and in reducing the force needed to inflate alveoli during inspiration . • B. Epithelial regeneration : type II pneumocytes can divide and regenerate both type I and type II pneumocytes . Neonatal Respiratory Distress Syndrome (RDS) Histological characteristics of specific regions of the respiratory portion of respiratory system •Alveolus histology : • Interalveolar septum : • Between neighboring alveoli lie thin Interalveolar septa consisting of scattered fibroblasts and scant ECM , mainly elastic and reticular fibers . • These fibers permit contraction and expansion of alveolar wall( during inspiration) and provide most of the structural support to the alveoli. • Alveolar pores of Kohn penetrate the Interalveolar septa and connect neighboring alveoli . • Capillary bed : which is a very extensive capillary bed consisting of continuous capillaries . Histological characteristics of specific regions of the respiratory portion of respiratory system • Blood -air barrier : • Air in the alveoli is separated from capillary blood by 3 components referred collectively as blood –air barrier ( respiratory membrane ) . • 1.Alveolar epithelial cells • 2.Basement membrane formed by fusion of epithelial cell basal lamina + capillary endothelial cell basal lamina. • 3.Capillary endothelial cells • Oxygen in alveolar air must diffuse across these layers to reach blood & carbon dioxide from the RBCs must diffuse across these layers to the alveolar space . Histological characteristics of specific regions of the respiratory portion of respiratory system • Dust cells : • are the alveolar macrophages • They are found both: • In the connective tissue of alveolar septum . • In the alveoli . • Dust cells phagocytose erythrocytes from damaged capillaries , foreign particles like inhaled dust , pollen etc. and are gradually passed up the alveolar tree in mucus until they are eliminated by swallowing . Respiratory portion of Respiratory system Pulmonary Vasculature • The lungs have a double blood supply : • Pulmonary vascular system • Bronchial vascular system • Pulmonary arteries from right side of the heart carry deoxygenated blood to the lungs. • Arterial branches follow the bronchial tree until the level of the respiratory bronchioles , at which point the network of continuous capillaries is formed . • The oxygenated blood enters the pulmonary veins .The pulmonary veins exit at the hilum of the lung and carry oxygenated blood to the left side of the heart . • Bronchial arteries also enter the lung hilum , branch along the bronchial tree , distributing blood to the level of respiratory bronchioles and then join the capillary network (pulmonary artery) , drained by pulmonary venules. • Venules are found singly in the lung parenchyma . After small pulmonary veins leave a lobule, they follow the bronchial tree towards the hilum . Pleura • The pleura is a simple squamous epithelium (mesothelium) with a fine layer of underlying connective tissue containing collagen and elastic fibers . • Visceral pleura • Parietal pleura • Space between visceral and parietal pleura is pleural cavity filled with a serous fluid , that reduces friction during lung expansion . • Mesothelioma is a tumor that originates in the mesothelial cell lining of the pleura, the peritoneum, and the pericardium. • Mesothelioma is associated with previous long exposure (15 to 40 years) to asbestos. Pleural mesothelioma spreads within the thoracic cavity (pericardium or diaphragm, and metastasis can involve any organ, including the brain. Review of Respiratory System Features of airways within the lungs Respiratory system