Respiratory System Histology PDF - Dr. Austria, AY 2020-2021

(009) RESPIRATORY SYSTEM HISTOLOGY DR. AUSTRIA | 11/24/2020 OUTLINE  Most of the respiratory structures are lined by...

(009) RESPIRATORY SYSTEM HISTOLOGY DR. AUSTRIA | 11/24/2020 OUTLINE  Most of the respiratory structures are lined by pseudostratified ciliated columnar with goblet cells I. RESPIRATORY EPITHELIUM epithelium. A. Conducting portion B. Respiratory portion C. 5 Major Cell Types 1. Ciliated columnar cells 2. Goblet cells 3. Basal cells 4. Brush cells 5. Small granule cells II. OLFACTORY EPITHELIUM A. 3 Major Cell Types 1. Olfactory neurons 2. Supporting cells 3. Basal cells III. CONDUCTING PORTION A. Nasal cavities B. Nasopharynx and posterior oropharynx C. Larynx D. Trachea E. Bronchioles F. Terminal bronchioles IV. RESPIRATORY PORTION A. Respiratory Bronchioles B. Alveolar ducts and sacs C. Alveoli 1. Type I Alveolar cell C. 5 Major cell types 2. Type II Alveolar cell 1. Ciliated columnar cells are the most abundant D. Alveolar Macrophages (Dust cells) cells that extend the entire thickness of the V. TEST YOURSELF epithelium. The cilia sweep the surface of the epithelium and protect the lungs by removing VI. small inhaled particles. Each with 250-300 cilia on its apical surface. I. Respiratory Epithelium - most of the nasal cavities and conducting portion of the system is 2. Goblet cells are numerous in the more proximal lined with mucosa having ciliated pseudostratified columnar airways and gradually decrease in number toward epithelium. the distal parts of the respiratory tube. These cells contain and release mucus glycoproteins to form Components: a protective layer on the epithelial surface. A. Conducting portion With basal nuclei and apical domains filled with granules of mucin glycoproteins. - consists of passageways or tubes outside (extrapulmonary) and inside (intrapulmonary) of 3. Basal cells are located close to the basal lamina the lungs that conduct air for gaseous exchange without their apices reaching the lumen of the to and from the lungs. epithelium. These cells serve as stem cells for - nasal cavities, pharynx, larynx, trachea, bronchi continual replacement of other epithelial (Gr. bronchos, windpipe), bronchioles, and cells.They replace epithelial cells that have been terminal bronchioles. destroyed by injury. - conducting portion cleans and humidifies inspired 4. Brush cells are less numerous than the other air and provides conduits for air movement to and cells. Because their basal surfaces contact from alveoli. afferent nerve endings, it is believed that these cells function as receptor cells. B. Respiratory portion - consists of passageways within the lungs that not Brush cells are chemosensory receptors only conduct the air but also allow respiration or resembling gustatory cells, with similar signal gaseous exchange transduction components and synaptic contact - respiratory bronchioles, alveolar ducts, and with a$erent nerve endings on their basal alveoli surfaces. PREPARED AND EDITED BY: LAPIDEZ, R., LAZO, R., LEONARDIA, R., LEONES, C., OLUKOKUN, S., ORENIA, R., OROZO, M., PA-A, A.  (009) RESPIRATORY SYSTEM HISTOLOGY DR. AUSTRIA | 11/24/2020 5. Small granule cells (Kulchitsky cells) contain cells to the olfactory cells. numerous membrane-bound granules and are - they express abundant ion channels that help maintain a analogous to the enteroendocrine cells of the microenvironment conducive to olfactory function and diffuse neuroendocrine system (DNES). These survival cells also function as receptor cells. 3. Basal cells Like enteroendocrine cells of the gut, they are - are small, spherical or cone-shaped cells near the basal part of the diffuse neuroendocrine system lamina (DNES). Represent only about 3% of the cells in - these are the stem cells for the other two types, replacing respiratory epithelium. the olfactory neurons every 2-3 months and support cells less frequently. RESPIRATORY EPITHELIUM Figure 2. Olfactory epithelium. Shows the transition from respiratory to olfactory epithelium. The left portion, the olfactory epithelium, cells are devoid of cilia and goblet cells. The presence of bowman’s gland is visible in olfactory epithelium. The function of the bowman's gland is to introduce odoriferous particles in this nerve to perform its function, to identify its smell.. While on the right, the respiratory Figure 1. a) Respiratory epithelium showing the pseudostratified epithelium, cilia and goblet cells are present. ciliated columnar (C) with goblets cells (G). b) Electron microscopy picture of respiratory epithelium. c) High magnification image of cilia. The lamina propria of the olfactory epithelium possess large serous glands, the olfactory glands (of Bowman), which produce a II. Olfactory Epithelium constant flow of fluid surrounding the olfactory cilia and facilitating the access of new odoriferous substances. Highly specialized sensory pseudostratified epithelium RESPIRATORY SYSTEM Lacks goblet cells or motile cilia on its cells CONDUCTING PORTION RESPIRATORY PORTION A. 3 Major cell types: - Nasal cavities - Respiratory bronchioles - Pharynx - Alveolar ducts and sacs 1. Olfactory neurons - Larynx - Alveoli - are sensory bipolar neurons that are distributed - Trachea between the more apical supportive cells and the - Bronchi basal cells present throughout the epithelium. - Terminal bronchioles the receptors respond to odoriferous the substances by generating an action potential along the axons extending from basal ends of these neurons III. Conducting portion - the axons leave the epithelium and unite in the A. Nasal cavities lamina propria as very small nerves that then pass - Divided based on the epithelium covering the nasal to the brain through foramina in the cribriform plate cavities. of the ethmoid bone. Vestibules of the nasal cavities - they form the olfactory nerve (CN I) and ○ outermost part eventually synapse with neurons in the olfactory ○ Epithelium: Stratified squamous, kereatinized to bulb of the brain. nonkeratinized (as you go to the mucosa) ○ Glands: Sebaceous and sweat glands 2. Supporting cells ○ Musculoskeletal support: Hyaline cartilage - Gives support to the survival or function of olfactory ○ Features and functions: Vibrissae (stiff hairs) and epithelium. moisture both filter and humidify air - are columnar, with narrow bases and broad, cylindrical Most areas of nasal cavities apexes containing the nuclei and extending microvilli into ○ Epithelium: Respiratory the fluid layer ○ Glands: Seromucous glands - Well-developed junctional complexes bind the supporting ○ Musculoskeletal support: Bone and hyaline PREPARED AND EDITED BY: LAPIDEZ, R., LAZO, R., LEONARDIA, R., LEONES, C., OLUKOKUN, S., ORENIA, R., OROZO, M., PA-A, A.  (009) RESPIRATORY SYSTEM HISTOLOGY DR. AUSTRIA | 11/24/2020 cartilage Usually composed of cartilages ○ Features and functions: Rich vasculature (in order Epithelium: Respiratory to humidity or warm the air we inhale) and glands; Glands: Mainly mucous glands, some serous or mixed warm, humidify, and clean air glands Superior areas of nasal cavities Musculoskeletal support: C-shaped rings of hyaline ○ where olfactory nerve is located cartilage, with smooth (trachealis) muscle in posterior ○ Epithelium: Olfactory epithelium, with bipolar opening of each. Usually 20 of them neurons ○ A series with about a dozen C-shaped rings of ○ Glands: Serous (Bowman) glands (secretes a hyaline cartilage between the submucosa and serous secretion, aids to the introduction of adventitia reinforces the wall and keeps the odoriferous in order to identify the smell) tracheal lumen open. ○ Musculoskeletal support: Bone (ethmoid) Features and functions: Conduct air to primary bronchi ○ Features and functions: Solubilize and detect entering lungs odorant molecules in air Smooth Trachealis muscle is located posteriorly The open ends of the cartilage rings are on the posterior B. Nasopharynx and posterior oropharynx surface, against the esophagus, and are bridged by a bundle of smooth muscle called the trachealis muscle and a Epithelium: Respiratory and stratified squamous epithelium sheet of fibroelastic tissue attached to the perichondrium Glands: Seromucous glands Trachealis muscle- relaxes during Musculoskeletal support: Bone and skeletal muscle swallowing to facilitate the passage of Features and functions: Conduct air to larynx; pharyngeal food by allowing the esophagus to bulge and palatine tonsils. into the lumen of the trachea, with the - If these structures are enlarged, they would have an elastic layer preventing excessive influence in the conduction of air towards the larynx. distention of the lumen. The muscle Enlargement of these impedes the conduction of air. strongly contracts in the cough reflex to narrow the tracheal lumen and provide Nasopharynx is continuous caudally with the oropharynx for increased velocity of the expelled air (throat), the posterior part of the oral cavity leading to the and better loosening of material in the larynx and esophagus. air passage. Unlike the stratified squamous epithelium of the oropharynx, the nasopharynx lining is respiratory epithelium, and its mucosa contains the medial pharyngeal tonsil and the openings of the two auditory tubes which connect to each middle ear cavity C. Larynx The Vocal cords short (4 cm × 4 cm) passage for air between the pharynx and the trachea Epithelium: Respiratory and stratified squamous epithelium - At the level of true vocal cords, stratified squamous epithelium is seen because squamous cells are more resilient to stress or pressure, unlike respiratory cells. Larynx is exposed to high velocity of air coming in and out of trachea. Glands: Mucous glands (predominantly), smaller seromucous glands Musculoskeletal support: Elastic and hyaline cartilage, ligaments, skeletal muscle all of which are connected by ligaments. ❏ Hyaline Cartilage: in the thyroid, cricoid, and the inferior arytenoid cartilages ❏ Elastic Cartilage: in the epiglottis, cuneiform, corniculate, and the superior arytenoid cartilages Features and functions: Site of phonation In addition to maintaining an open airway, movements of these cartilages by skeletal muscles participate in sound production during phonation. D. Trachea 10-12 cm long in adults, is lined with typical respiratory mucosa in which the lamina propria contains numerous seromucous glands producing watery mucus PREPARED AND EDITED BY: LAPIDEZ, R., LAZO, R., LEONARDIA, R., LEONES, C., OLUKOKUN, S., ORENIA, R., OROZO, M., PA-A, A.  (009) RESPIRATORY SYSTEM HISTOLOGY DR. AUSTRIA | 11/24/2020 E is the epithelium. CT is the cartilage which decrease in number compared to upper airway. E. Bronchi Epithelium: Respiratory Musculoskeletal support: Prominent spiral bands of smooth muscle; irregular hyaline cartilage plates Features and functions: Repeated branching; conduct aire deeper into lungs The mucosa of the larger bronchi is structurally similar to the tracheal mucosa except for the organization of cartilage and smooth muscle. In the primary bronchi most cartilage rings completely encircle the lumen, but as the bronchial diameter decreases, cartilage rings are gradually replaced with smaller isolated plates of hyaline cartilage. Small mucous and serous glands are abundant, with ducts opening into the bronchial lumen. The lamina propria also contains crisscrossing bundles of spirally arranged smooth muscle and elastic fibers (Figures 17–7 and 17–8), which become more prominent in the smaller bronchial branches. Contraction of this muscle layer is responsible for the folded appearance of the bronchial mucosa observed histologically in cross sections. F. Bronchioles Are the intralobular airways with diameters of 1mm or less, formed after about the tenth generation of branching; they lack both mucosal glands and cartilage, although dense connective tissue is associated with the smooth muscle. In the larger bronchioles, the epithelium is still ciliated pseudostratified columnar, but this decreases in height and complexity to become ciliated simple columnar or simple cuboidal epithelium in the smallest terminal bronchioles, which are the last parts of the air conducting system. The ciliated epithelial lining of bronchioles begins the mucociliary apparatus or escalator, important in clearing debris and mucus by moving it upward along the bronchial tree and trachea. Epithelium: Simple ciliated cuboidal to columnar, with exocrine club cells Musculoskeletal support: Prominent circular layer of smooth muscle; no cartilage Features and functions: Conduct air; important in bronchoconstriction (would collapse upon this action) and bronchodilation. PREPARED AND EDITED BY: LAPIDEZ, R., LAZO, R., LEONARDIA, R., LEONES, C., OLUKOKUN, S., ORENIA, R., OROZO, M., PA-A, A.  (009) RESPIRATORY SYSTEM HISTOLOGY DR. AUSTRIA | 11/24/2020 G. Terminal Bronchioles Epithelium: Simple cuboidal, ciliated cells and club cells, with Each terminal bronchiole subdivides into two or more scattered alveoli respiratory bronchioles that include saclike alveoli and Musculoskeletal Support: Fewer smooth muscle fibers, represent, therefore, the first-part of this system’s mostly around alveolar openings respiratory region. Features and Functions: Conduct air deeper, with some gas The respiratory bronchiolar mucosa resembles that of the exchange, and protective and surfactant functions of club terminal bronchioles, except for having a few openings to cells. alveoli where gas exchange occurs. Smooth muscle and elastic connective tissue comprise the B. Alveolar ducts and sacs lamina propria and the epithelium consists of club cells, with simple squamous cells at the alveolar openings and Epithelium: Simple cuboidal between many alveoli extending into the alveolus. Proceeding distally along the Musculoskeletal Support: Bands of smooth muscle around respiratory bronchioles, alveoli become more numerous alveolar openings. Features and Functions. Conduct air, with and closer together. much gas exchange Transition between conducting and respiratory zone Epithelium: Simple cuboidal, ciliated cells and club cells ALVEOLAR DUCTS (Clara cells) replaces goblet cell *Clara cells - cuboidal non-ciliated cells that has three Distal ends of respiratory bronchioles branch into tubes functions: called alveolar ducts that are completely lined by the 1. They produce one of the components of openings of alveoli surfactant Both the alveolar ducts and the alveoli themselves are lined 2. They act as stem cells with extremely attenuated squamous cells 3. They contain enzyme systems which can detoxify In the thin lamina propria, a strand of smooth muscle cells noxious substances surrounds each alveolar opening and a network of elastic Musculoskeletal support: Thin, incomplete circular layer of and collagen fibers supports both the duct and its alveoli. smooth muscle; no cartilage ALVEOLAR SACS Features and functions: Conduct air to respiratory portions of lungs; exocrine club cells with several protective Larger clusters of alveoli surfactant functions form the ends of alveolar ducts distally and occur occasionally along their length. The lamina propria is now extremely thin, consisting essentially of a web of elastic and reticular fibers that encircles the alveolar openings and closely surrounds each alveolus. Prominent in this sparse connective tissue, a network of capillaries also surrounds each alveolus. No cartilage present. Smooth muscle surround the lumen of the terminal bronchioles. Epithelium becomes simple columnar without cilia from pseudostratified with cilia. C. Alveoli IV.RESPIRATORY PORTION Saclike evaginations, each about 200 μm in diameter, from the respiratory bronchioles, alveolar ducts, and alveolar A. Respiratory bronchioles sacs. Responsible for the spongy structure of the lungs Functions for gas exchange Each adult lung has approximately 200 million alveoli with a total internal surface area of 75 m2. Each alveolus resembles a small rounded pouch open on one side to an alveolar duct or alveolar sac. PREPARED AND EDITED BY: LAPIDEZ, R., LAZO, R., LEONARDIA, R., LEONES, C., OLUKOKUN, S., ORENIA, R., OROZO, M., PA-A, A.  (009) RESPIRATORY SYSTEM HISTOLOGY DR. AUSTRIA | 11/24/2020 Air in these structures exchanges O2 and CO2 with the blood Alveolar lining Fluids in surrounding capillaries, through thin specialized alveolar walls that enhance diffusion between the external and - Also removed via the conducting passages as a result of the internal environments ciliary activity, they combine with bronchial mucus to form Epithelium: Types I and II alveolar cells (pneumocytes) bronchoalveolar fluid Musculoskeletal Support: None (but with network of elastic and reticular fibers) Bronchoalveolar fluid Features and Functions: Sites of all gas exchange; - helps remove particulate components from inspired air. surfactant from type II pneumocytes; dust cells - bacteriostatic, containing lysozyme and other protective agents produced by club cells, type II alveolar cells, and 1. Type I Alveolar cells alveolar macrophages. Type I pneumocytes Cover 97% of all alveolar cells are extremely thin simple squamous cells that line the alveoli and are the main sites for gaseous exchange thin that the TEM was needed to demonstrate that all alveoli have such linings Organelles here are also grouped around the nucleus, reducing the thickness of the remaining cytoplasm at the blood-air barrier to as little as 25 nm are in very close contact with the endothelial lining of capillaries, forming a very thin blood-air barrier for gaseous exchange all type I epithelial cells have tight junctions that prevent the leakage of tissue fluid into the alveolar air space 2. Type II Alveolar cells Type II pneumocytes or septal cells fewer in number and cuboidal in shape that bulge into the air space, interspersed among the type I alveolar cells and bound to them with tight junctions and desmosomes. They appear singly or in groups adjacent to the squamous type l alveolar cells within the alveoli These cells synthesize and secrete a phospholipid-rich product called pulmonary in surfactant Can function as stem cells for type I squamous alveolar cell replacement in the alveoli during lung injury These epithelial cells rest on the same basal lamina and have the same origin as the type I cells that line most of the alveolus Type II cell nuclei are rounded and may have nucleoli, and Type 1 cells are secreted just adjacent to capillaries, appear thinner their cytoplasm is typically lightly stained with many vesicles and flat. Alveolar macrophages take up the appearance of dust after carbon dioxide particles are phagocytosed. D. Alveolar Macrophages or Dust Cells Are blood monocytes that have entered the pulmonary TEST YOURSELF connective tissue septa and alveoli 1. Cuboidal non-ciliated cells that functions in detoxification of The primary function of these macrophages is to clean the noxious substances? alveoll of invading microorganisms and inhaled particulate 2. They are singly or in groups adjacent to Type I alveolar cells. matter by phagocytosis. 3. Contains numerous membrane-bound granules and are analogous They can be found in the alveoli or in the connective tissue to enteroendocrine cells of the diffuse neuroendocrine system septa by their phagocytosed particulate or carbon particles. (DNES). Active alveolar macrophages can often be distinguished 4. Acts primarily to clean the alveoli from invading microorganisms from type II pneumocytes because they are slightly darker and inhaled particulate matter. due to their content of dust and carbon from air and complexed iron (hemosiderin) from erythrocytes 5. Composed of simple cuboidal cells located between many alveoli that functions as conduit of air with much gas exchange. Filled macrophages have various fates: 6. What cells can serve as stem cells for replacing type I alveolar cells? 1. Most migrate into bronchioles where they move up the A. Goblet cells mucociliary apparatus for removal into the esophagus; B. Septal cells 2. Others exit the lungs in the lymphatic drainage; and C. Type II alveolar cells 3. Some remain in the interalveolar septa connective tissue for D. Blood monocytes years. E. Type I alveolar cells PREPARED AND EDITED BY: LAPIDEZ, R., LAZO, R., LEONARDIA, R., LEONES, C., OLUKOKUN, S., ORENIA, R., OROZO, M., PA-A, A.  (009) RESPIRATORY SYSTEM HISTOLOGY DR. AUSTRIA | 11/24/2020 7. Which cells in the alveoli contain lamellar bodies in their cytoplasm? A. Type I alveolar cells B. Type II alveolar cells C. Goblet cells D. Septal cells E. All alveolar cells 8. What is the main function of surfactant? A. To reduce air flow into the lung B. To increase air flow into the lung C. To reduce alveolar surface tension D. To reduce the alveolar lumina E. To decrease the blood-air barrier 9. Which cells serve as stem cells for renewing the olfactory epithelium? A. Goblet cells B. Sustentacular cells C. Ciliated cells D. Basal cells E. Connective tissue cells 10. The serous secretory substance in which odorant molecules dissolve is produced by: A. Olfactory (Bowman) glands B. Olfactory vesicles C. Goblet cells D. Olfactory Cilia E. Basal cells ANSWERS 1. Clara cells 2. Type II Alveolar cells 3. Small granule cells (Kulchitsky cells) 4. Alveolar Macrophage or Dust cells 5. Alveolar ducts and sacs. 6. C 7. B 8. C 9. D 10. A REFERENCES Mescher, A. L., & Junqueira, L. C. U. (2018). Junqueira's basic histology: Text and atlas. New York (NY: McGraw-Hill Education Eroschenko, V. P., & Di, F. M. S. H. (2017). DiFiore's atlas of histology with functional correlations PREPARED AND EDITED BY: LAPIDEZ, R., LAZO, R., LEONARDIA, R., LEONES, C., OLUKOKUN, S., ORENIA, R., OROZO, M., PA-A, A.  (009) RESPIRATORY SYSTEM HISTOLOGY DR. AUSTRIA | 11/24/2020 APPENDIX PREPARED AND EDITED BY: LAPIDEZ, R., LAZO, R., LEONARDIA, R., LEONES, C., OLUKOKUN, S., ORENIA, R., OROZO, M., PA-A, A.  (009) RESPIRATORY SYSTEM HISTOLOGY DR. AUSTRIA | 11/24/2020 PREPARED AND EDITED BY: LAPIDEZ, R., LAZO, R., LEONARDIA, R., LEONES, C., OLUKOKUN, S., ORENIA, R., OROZO, M., PA-A, A.