Respiratory System PDF - ANAT2241

Respiratory System ANAT2241: Histology JOYCE EL-HADDAD [email protected] @orientatewithjoyce Lecture Outline • Function and structure of the respiratory system • Tracheobronchial tree • Histology of the respiratory system Learning Outcomes: LO1. To understand the function and components o...

Respiratory System ANAT2241: Histology JOYCE EL-HADDAD [email protected] @orientatewithjoyce Lecture Outline • Function and structure of the respiratory system • Tracheobronchial tree • Histology of the respiratory system Learning Outcomes: LO1. To understand the function and components of respiratory system LO2. To understand the histological features of the upper and lower respiratory tract LO3. To understand the histological architecture of bronchial tree LO4. To understand the differences between bronchi and bronchioles LO5. To understand the types of cells in alveoli Textbook reference: Netter’s Essential Histology Overall Function of the Respiratory System The gas exchange: CO2 and O2 btw the organism and the external environment. LO1. To understand the function and components of respiratory system The respiratory system – Anatomical Classification Anatomical divisions: • The upper respiratory tract: nose, pharynx and associated structures; • The lower respiratory tract: larynx, trachea, bronchi and lungs. LO1. To understand the function and components of respiratory system Anatomical vs Functional Classification Anatomical Classification: • The upper respiratory tract: nasal cavity, pharynx and associated structures; Functional Classification: • Conductive portion: filtering, humidifying, & moistening the air. When you hear the word ‘moist’ • The lower respiratory tract: larynx, trachea, bronchi and lungs. • Respiratory portion: site of gas exchange. LO1. To understand the function and components of respiratory system Respiratory Epithelium o Respiratory epithelium lines most the nasal cavities, and conducting portion of the respiratory system o Respiratory epithelium = Pseudostratified Ciliated Columnar Epithelium o There are 5 major types of cell in respiratory epithelium: 1) Ciliated Columnar cells (~250 cilia on each cell) 2) Goblet cells – mucous production 3) Brush cells (chemosensory receptors) – columnar cells with blunt microvilli (very few) 4) Small granule cells - endocrine function 5) Basal cells - function? • Location: Ø Ø Ø Ø Most of the nasal cavity – nasopharynx Paranasal sinuses Most of the larynx Trachea Nasal Cavity • The pseudostratified ciliated columnar epithelium of the mucous membrane has abundant, unevenly distributed mucussecreting goblet cells. Many branched seromucous glands extend into the underlying lamina propria and are connected to the surface via small ducts. • In the lamina propria are large venous plexuses. Their major role is to warm inspired air via heat exchange. 336 Respiratory System Low-magnif nasal concha. R externally and is i lumen (*). Its cen contains several t trabeculae (B). A drained by a duct 100×. H&E. * B V * LARYNX- a short passage for air between the pharynx and the trachea • • • Vestibular fold: Respiratory epithelium Vocal cord (VC): Nonkeratinized stratified squamous epithelium Vocal ligament: elastic connective tissue Vocalis muscle (VM): large bundles of striated fibers Tracheo-Bronchial Tree Trachea > Primary bronchi > Secondary (lobar) bronchi > Tertiary (segmental) bronchi > Bronchioles > Terminal bronchioles > Respiratory bronchioles > Alveolar ducts > Alveolar sacs > Alveoli* *Purple = conducting portion Pink = Respiratory portion LO3. To understand the histological architecture of bronchial tree Trachea: 1. Mucosa: - Epithelium: Lined with typical respiratory epithelium - Lamina propria (LP) 1. Lumen 1 2. Submucosa: - Slightly denser CT than LP - Seromucous glands 3. Musculo-cartilaginous layer: - A series of C-shaped hyaline cartilage rings - Trachealis muscle 4. Adventitia: - Connective tissue that binds trachea to adjacent structures Tracheo-Bronchial Tree Trachea > Primary bronchi > Secondary (lobar) bronchi > Tertiary (segmental) bronchi > Bronchioles > Terminal bronchioles > Respiratory bronchioles > Alveolar ducts > Alveolar sacs > Alveoli* *Purple = conducting portion Pink = Respiratory portion LO4. To understand the differences between bronchi and bronchioles Bronchi 1. Mucosa: - Epithelium: Lined with typical respiratory epithelium - Lamina propria (LP) + lymphatic tissue 2. Muscularis - Smooth muscle and elastic fibers Lumen 1 1. Lumen 3. Submucosa - Slightly denser CT than LP - Seromucous glands 4. Cartilaginous: - Discontinued hyaline cartilage plates 5. Adventitia: - Connective tissue that binds bronchi to adjacent structures LO4. To understand the differences between bronchi and bronchioles Respiratory System 343 Schematic section of a large bronchus. Ciliated columnar epithelium with numerous goblet cells Basal cells lined up on basement membrane Lamina propria with elastic fibers, blood vessels, and lymphatics Smooth muscle Submucosal glands Nerve fascicle Hyaline cartilage plate surrounded by perichondrium Blood vessels Lymph vessel * SD RE SM MA HC LM section of the wall of a bronchus. Ciliated respiratory epithelium (RE) lines the lumen (*). Smooth muscle (SM) is in the underlying lamina propria. A plate of hyaline cartilage (HC) is situated on the outer aspect of the airway. A seromucous gland appears to the right. 300×. H&E. LO4. To understand the differences between bronchi and bronchioles LM of a bronchial seromucous gland. It contains pale-stained mucous acini (MA), darkly stained serous demilunes (SD), and flattened myoepithelial Tracheo-Bronchial Tree Trachea > Primary bronchi > Secondary (lobar) bronchi > Tertiary (segmental) bronchi > Bronchioles > Terminal bronchioles > Respiratory bronchioles > Alveolar ducts > Alveolar sacs > Alveoli* *Purple = conducting portion Pink = Respiratory portion LO4. To understand the differences between bronchi and bronchioles Bronchioles o Bronchioles lack mucosal glands and cartilage o Larger bronchioles are lined with respiratory epithelium o Smaller, terminal bronchioles lined with either simple ciliated columnar/cuboidal epithelium Mucociliary escalator LO4. To understand the differences between bronchi and bronchioles Terminal Bronchioles - Thin, incomplete circular layer of smooth muscle - No cartilage - Functionally, the last part of the conducting portion - Epithelium consists of simple ciliated cuboidal cells and club cells CLUB CELLS: - Non ciliated, apical end of the cells are dome shaped and their cytoplasm contains secretory granules - Function: i. Secretion of surfactant, and mucin. ii. Detoxification of xenobiotic compounds iii. Immune defense LO4. To understand the differences between bronchi and bronchioles Respiratory Bronchioles - Presence of alveoli in the wall of the respiratory bronchioles; always include saclike alveoli - Epithelium: • Ciliated cuboidal cells • Club cells • Simple squamous cells at the alveolar openings and extending into the alveolus LO4. To understand the differences between bronchi and bronchioles Tracheo-Bronchial Tree Trachea > Primary bronchi > Secondary (lobar) bronchi > Tertiary (segmental) bronchi > Bronchioles > Terminal bronchioles > Respiratory bronchioles > Alveolar ducts > Alveolar sacs > Alveoli* *Purple = conducting portion Pink = Respiratory portion LO4. To understand the differences between bronchi and bronchioles Alveolar Ducts & Sacs Alveolar Ducts: - simple cuboidal and thin squamous epithelium as you move towards sacs Alveolar Sacs: - Squamous cells and abundance of elastic and reticular fibers - Prominent network of capillaries Alveoli Saclike evaginations • Responsible for the spongy structure of the lungs • Each adult lung has approximately 200 million alveoli Cells: 1- Type I alveolar cells (or type I pneumocytes) 2- Type II alveolar cells (type II pneumocytes or septal cells) 3- Alveolar macrophages (dust cells) Type I alveolar cells (or type I pneumocytes) 348 • Make up about 95% of the alveolar lining • Have tight junctions that prevent the leakage of tissue fluid into the alveolar air space Respiratory System LM of the parenchyma lined by flattened type I pneu nuclei, and cuboidal type II p euchromatic nuclei. Pulmona erythrocytes traverse the inte macrophages (dust cells, DC ingested particulate matter. A vein (PV) has a thin wall and pulmonary capillaries. 675× PV PC II DC I Schematic of alveoli a Alveolar dust ce DC * II Alveolus (airspace) WBC * RBC I Type I cell with tight junctions 10 µm Type II alveolar cells (type II pneumocytes or septal 348 Respiratory System cells) • Cuboidal cells bulging into the air space • Synthesises and releases pulmonary surfactant • Lowers surface tension at the air-epithelium interface and helps prevent alveolar collapse at exhalation • Allows alveoli to be inflated with less inspiratory force, easing the work of breathing • Cell nuclei are more euchromatic relative to Type I pneumocyte – why? PV PC II LM of th lined by flatt nuclei, and c euchromatic erythrocytes macrophage ingested par vein (PV) ha pulmonary c DC I * Schema DC II 348 Respiratory System Alveolar macrophages (dust cells) • • LM of the parenchyma of the lung. Pulmonary alveoli are lined by flattened type I pneumocytes (I), with darkly stained nuclei, and cuboidal type II pneumocytes (II), with more euchromatic nuclei. Pulmonary capillaries (PC) filled with erythrocytes traverse the interalveolar septa. Alveolar macrophages (dust cells, DC) are clearly seen after they have ingested particulate matter. A small branch of the pulmonary vein (PV) has a thin wall and collects venous blood from the pulmonary capillaries. 675×. H&E. PV PC Found in alveoli and in the interalveolar septum II PV PC II Active alveolar macrophages can often be distinguished from type II pneumocytes because they are slightly darker due to their content of dust and carbon from air andDCcomplexed iron (hemosiderin) from erythrocytes I DC I Schematic of alveoli and interalveolar septum. Alveolar dust cell Type II cell DC * Capillary II Alveolus (airspace) DC * Alveolus (airspace) WBC II * Capillary RBC I Type I cell with tight junctions Interalveolar septum WBC RBC 10 µm EM of the alveoli of the lung. Red (RBC) and white (WBC) blood cells occupy lumina of pulmonary capillaries, which travel in interalveolar septa. Alveolar spaces (*) are lined by type I pneumocytes, which are best seen in the region of their elongated nuclei, and type II pneumocytes (II). Alveolar macrophages (dust cells, DC) in the interstitium are recognizable by their content of lysosomes. The area delineated by the rectangle is seen at higher magnification in Fig. 15.16. 1000×. (Courtesy of Dr. B. J. Crawford) I *