Respiratory Histology PDF

Respiratory System Histology  Introduction to Histology, Cell Structure and Function Connect to this resource at: Click on this link: Junqueria's Basic Histology: Text and Atlas 17th Ed. by: publication date: 2024. Available Online From: AccessMedicine. 15th available in pri...

Respiratory System Histology  Introduction to Histology, Cell Structure and Function Connect to this resource at: Click on this link: Junqueria's Basic Histology: Text and Atlas 17th Ed. by: publication date: 2024. Available Online From: AccessMedicine. 15th available in print on ReserveLinks. at Health Center Library. QS 504 J95h14 2016 Chapter 12: Respiratory System Learning Objectives for Respiratory System 1. Describe the structure, function and characteristics of the respiratory tract from the nasal passages to the alveoli. Describe the layers, including epithelium, other cells, connective tissues, etc. and compare/contrast these along the tract 2. Describe the development of the respiratory tract 3. Compare and contrast the conducting vs. the respiring portion of the respiratory tract 4. Describe the alveolar lining and cells and tissue associated with the alveolus and capillary network 5. Describe the blood supply to the lungs and two distance system 6. Describe the pleura of the lungs 7. Describe histologic sections of lung tissue  Respiratory System Conducting vs. Respiring (Terminal bronchioles + Alveoli) Lung Structure Normal Lung  Development of Respiratory System Endoderm gives rise to the epithelium and glands of the larynx, trachea, bronchi and the pulmonary epithelium Mesoderm gives rise to the connective tissue, cartilage and smooth muscle of the respiratory tract Development of Bronchi and Bronchioles The lung bud divides into two bronchial buds, which divide and form secondary and tertiary bronchi As bronchi develop, the surrounding mesenchyme forms cartilage, smooth muscle, connective tissue and capillaries Respiratory System Development Surfactant C Surfactant A, B Surfactants are important to maintain alveoli and prevent alveolar collapse  Trachea Primary bronchus Secondary bronchi Right lung Left lung Conducting portion Bronchiole (1 mm or less in diameter) Terminal bronchiole Respiratory bronchiole Alveolar duct Respiratory portion Alveolar sac Olfactory Tissue: Olfactory cells are bipolar neurons, that have odorant binding proteins on vesicles and send signals eventually to cranial nerve 1 Bowman’s glands send secretions to trap odorants Sustentacular cells are supporting cells Basal cells Clinical Correlation Covid-19 Disease Loss of smell  Larynx Epiglottis Trachea False True The larynx is shown opened anteriorly. The epiglottis is at the left and the upper trachea at the right. Note the vocal folds in the center. The false vocal fold (cord) is to the left and the true cord to the right, with the recess of the ventricle in between.  Larynx and Vocal Cords  Passageway for air between oropharynx and trachea, organ of speech (phonation) False  Ventricular folds- “false” vocal cords, ciliated columnar True epithelium  Vocal folds (cords)- two folds of mucosa, “true”- squamous type epithelium Clinical Correlation Bronchoscopy Summary- Histologic Features of Respiratory Tract Key Slide  Epithelium Mucosa Basement membrane Lamina propria Submucosa Glands Cartilage would be here  Conducting Epithelium  Location  Cilia  Secretory  Respiratory Epithelium Cell Types ⚫ Ciliated columnar cells: most abundant cell type. Cilia beat in unison and move mucus and trapped particles to oropharynx, where it is swallowed or expectorated ⚫ Goblet cells: produce mucus ⚫ Basal cells: stem cells that replenish epithelium ⚫ Brush cells: Columnar cells. No cilia but have apical microvilli ⚫ Neuroendocrine cells: epithelial cells containing hormones Respiratory (Conducting) Epithelium Pseudostratified columnar epithelium Goblet cells Cilia Goblet cells (G) and Cilia (C)  Respiratory Epithelium Pseudostratified Ciliated Columnar Goblet cells Cilia Pseudostratified columnar epithelium  Respiratory Epithelium Pseudostratified Ciliated Columnar Lumen Ciliated epithelial cells Goblet cells Basal cells  Clinical Correlation Asthma Normal ↑Goblet cells Goblet cell, ~5% ↑BM thickening ↑Inflammation BM Inflammation BM  Epithelium & Underlying Tissue Respiratory epithelium Connective tissue Glands Cartilage  Submucosal Glands & Underlying Tissue  Mucous and serous glands  Lymphoid tissue (BALT)  Smooth muscle  Cartilage- hyaline type  Adventitia  Trachea and Bronchi Right mainstem bronchus lies more vertical, in direct line with trachea. Increased likelihood for aspiration C-shaped cartilage rings with posterior membranous portion containing smooth muscle  Tracheal Respiratory Epithelium + Seromucous Glands and Cartilage  Bronchus/Bronchi ⚫ Trachea divides into two primary bronchi, which divide into secondary bronchi ⚫ Secondary bronchi divide into tertiary bronchi, which supply bronchopulmonary segments ⚫ Tertiary bronchi divide into smaller bronchi, which divide into bronchioles  Bronchus Bronchi undergo 9-12 branchings, as branching progresses:  Connective tissue decreases in thickness  Relative amount of smooth muscle and elastic tissue increases  Cartilage disappears (gone by bronchioles) Wall of Bronchus  Respiratory epithelium (E)  Lamina propria (LP)  Hyaline cartilage (C)  Nerves (N) and blood vessels (V)  Smooth muscle (SM) Note the order of structures: E → LP → SM → C (no cartilage)  Bronchioles ⚫ NO glands or cartilage ⚫ Larger bronchioles have respiratory epithelium. Smaller bronchioles have low columnar epithelium ⚫ In asthma, the smooth muscle in the bronchioles constricts, causing difficulty breathing Clinical Correlation Bronchiectasis Dilated airways ↑Mucus secretion ↑Inflammation a BV unit  Terminal Bronchioles ⚫ Simple cuboidal epithelium with cilia ⚫ Also: Clara cells (non- ciliated epithelial cells with secretory granules) ⚫ No goblet cells ⚫ Going down the respiratory tract, goblet cells are lost before cilia Clara cells: Make surfactant components, break down mucus, detoxify harmful substances, transfer IgA, fight bacteria Terminal Bronchiole and Beyond  Membranous Bronchioles to Alveoli  Bronchi divide to become bronchioles, when bronchi lose cartilage, it is now a bronchiole  Bronchioles further divide to become membranous than terminal bronchioles (< 2 mm diameter)  Distal to the terminal bronchiole (but including the terminal bronchiole) is the acinus or terminal respiratory unit  Pulmonary Lobule (and Acinus)  Smallest anatomic component of lung that is grossly apparent, separated by fibrous septa is called a lobule  Size ~1-2 cm diameter for lobule  Composed of ~ 5-10 acini ► An acinus is defined as the unit of lung distal to the last terminal bronchiole (also called membranous) ► Acinus is relevant from a radiological and pathological perspective  Bounded by a fibrous interlobular septum containing veins and lymphatics Respiratory Parenchyma-Gross BV= bronchovascular unit, Anthracotic Arteries branch (branches of the pulm. pigment artery) with airways to the periphery BV BV Parenchyma with pinpoint airways BV  Muscular artery Bronchovascular Unit Membranous bronchiole Conducting to Respiring Epithelium  Airways Preceding Alveoli ⚫ Respiratory bronchioles ► Going distally along the respiratory bronchioles, alveoli increase in number ► Cilia are gone by the end of the respiratory bronchiole ⚫ Alveolar ducts ► Back-to-back alveolar openings along wall ► Smooth muscle between alveolar openings looks like knobs Respiratory Bronchiole  Acinus or Acini  “Functional unit of lung”  Consists of terminal bronchiole, respiratory bronchiole, alveolar duct and sac Alveolar Duct (AD) leading to Alveolar Saccules (AS) Empysema Normal area Pleura Centrilobular emphysema Lobule  Alveoli ⚫ Sac-like structures with thin walls so O2 and CO2 can diffuse between air and blood ⚫ Separated by inter-alveolar septae, which contain capillaries ⚫ Cells lining inter-alveolar septae: ► Type I cells (thin, flat squamous cells) ► Type II cells (produce surfactant) Type I ► Alveolar macrophages (dust cells) Type II  Interstitial Fibroblast Cap Cap Alveolus Interstitial Type I Fibroblasts PAM Type II  Respiring Portion of the Lung Alveolus: Type I pneumocytes Type II pneumocytes Surfactant Macrophages Interstitial Space: Fibroblasts Matrix Components Capillary: Endothelium Blood cells  Alveoli Pores of Kohn  Type I Pneumocytes ⚫ Cover 95% of alveolar surface ⚫ Simple squamous cells with thin cytoplasm ⚫ Blood-air barrier includes (from air to blood): ► Type I cells ► Fused basal laminae of type I cells and capillary endothelial cells ► Capillary endothelial cellscells  Clinical Correlation Edema- Injury to Type I pneumocytes Pulmonary edema Congested vessels  Type II Pneumocytes ⚫ Cover 5% of alveolar surface ⚫ Large cuboidal cells with round nuclei ⚫ Typical secretory cell structure. Lamellar bodies in cytoplasm make and store surfactant ⚫ Surfactant decreases surface tension in alveoli and prevents collapse of alveoli during expiration Surface Tension, Surfactant & Alveoli Surfactant liquid lining of alveoli causes VERY LOW surface tension in alveoli Surfactant made by Type II pneumocytes By LaPlace’s law: P = 2T / r (P = pressure in sphere; T = surface tension; r = radius of sphere) With lower surface tension, needs less pressure to keep sphere open, if no or low surfactant, alveoli collapses Type II Pneumocyte  Pulmonary Alveolar Macrophages ⚫ Found on surface or in lumens of alveoli, within alveoli and in interstitial connective tissue, derived from blood monocytes ⚫ Remove debris and particles (phagocytic cells) that escape mucus and cilia in conducting portion of respiratory tract, sometimes called dust cells  Clinical Correlation Smoking Smokers’ Macrophages  Interstitium  Consists of the basement membrane of the endothelial and epithelial cells, collagen and elastic fibers, fibroblasts and a few mononuclear cells  Clinical Correlation Fibrosis in ARDS Later stage Thickened hyaline membranes Type II pneumocyte hyperplasia Interstitial fibrosis  Respiratory Blood Supply  Dual arterial supply  Pulmonary arteries (low pressure): ► Branches run alongside bronchi and bronchioles ► Progressively divide into capillary network in alveolar wall  Bronchial arteries (high pressure): ► Aortic (systemic) origin ► Branches run alongside bronchi to respiratory bronchioles  Intra- pulmonary Circulation  Parietal and Visceral Pleura  The outer surface of the lung and the inner surface of the thoracic cavity are covered by the pleura, which is a serous membrane (serosa)  Parietal pleura lines the thoracic cavity; visceral pleura covers the lungs  Serous membranes consist of simple squamous epithelial cells called mesothelium plus a thin layer of connective tissue  The pleural cavity contains serous fluid made by the pleura  Pleura  Visceral Pleural: covers and adheres to lung  Parietal Pleura: lines and adheres to Fluid between layers walls of the thoracic cavity  Pleural cavity: filled with serous fluid  Pleural Lymphatics  Follow bronchovascular structures and are found in pleura and interlobular septa ► Identified along Visceral pleura pulmonary arteries, airways to the level of the respiratory bronchioles, venules in the periphery of lobules and veins in the interlobular septa ► Rich lymphatic network in Alveolar visceral pleura space  Summary- Key Points  Conducting vs. respiring portions of the respiratory system  Tissue layers and cellular/tissue components of the respiring and conducting structures of the respiratory tract, trachea, bronchi, bronchioles, respiratory and terminal bronchioles  Non-cellular components of the lung, collagen and elastin  The pulmonary acinus, its component structures on the alveolar side, interstitium and capillary side  Pulmonary circulation and bronchial circulation and lymphatics in the lung  Pleura- two components 1) Go to PathPresenter: Website: https://cwru.pathpresenter.net Username: Your Case ID (i.e., [email protected]) Password: Your Case Password or just click “Login with SSO” 2) Click on words of each slide, i.e., first slide is hyperlinked, make sure your cursor is on the word “Trachea” hhttps://cwru.pathpresenter.net/#/public/display?token=282b9e6e). Trachea Trachea https://cwru.pathpresenter.net/public/display?token=3f598add Bronchus Bronchus https://cwru.pathpresenter.net/#/public/display?token=8abf4042 Lung Parenchyma Lung Parenchyma https://cwru.pathpresenter.net/#/public/display?token=1f45578f