Lower Respiratory System PDF

RESPIRATORY SYSTEM (Lower) Figen KAYMAZ, MD, PhD. Prof of Histology and Embryology 1 Upper respiratory tract Sphenoidal sinus Frontal sinüs Nasal cavity Pharynx Lower respiratory tract Larynx Trachea Bronchi Lungs 2 Functionally the respiratory system is subdivided into two major components: 1...

RESPIRATORY SYSTEM (Lower) Figen KAYMAZ, MD, PhD. Prof of Histology and Embryology 1 Upper respiratory tract Sphenoidal sinus Frontal sinüs Nasal cavity Pharynx Lower respiratory tract Larynx Trachea Bronchi Lungs 2 Functionally the respiratory system is subdivided into two major components: 1. Conducting portion: that conveys air from outside the body to the lungs. which consists of the nasal cavities, nasopharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles 2. Respiratory portion: where exchange of gases between the air and blood occurs. consisting of respiratory bronchioles, alveolar ducts, and alveoli 3 1. The conducting portion; air from the external milieu to the lungs. Extrapulmoner: – Nose (nasal cavity), – Paranasal sinuses – mouth, – nasopharynx, – pharynx, – larynx, These structures not only transport but also filter, moisten, and warm the inspired air before it reaches the respiratory portion of the lungs. – trachea, Intrapulmoner – primary bronchi, – secondary bronchi (lobar bronchi), – tertiary bronchi (segmental bronchi), – bronchioles, – terminal bronchioles. 4 2. Respiratory portion; where gas exchange takes place. Consisting of üRespiratory bronchioles üAlveolar ducts üalveoli 5 THE TRACHEA The trachea has three layers: 1. mucosa, • • Epithelium LP: 2. Submucosa, 3. Adventitia, 16-20 C-shaped hyaline cartilage keep the tracheal lumen open, open ends are located on the posterior surface, fibroelastic lig. and a bundle of smooth muscle (trachealis muscle) bind to the perichondrium 6 HISTOLOGY OF THE TRACHEA • mucosa, – respiratory epithelium: pseudostratified ciliated columnar epithelium with goblet cells – lamina propria: loose connective tissue rich in elastic fibers and contains diffuse lymphoid tissue and scattered lymphatic nodules. • the submucosa: – seromucous glands • hyaline cartilage rings: • the adventitia; outermost tunic – loose connective tissue 7 8 HISTOLOGY OF THE TRACHEA Epithelium of trachea 1. 2. 3. 4. 5. Ciliated cells Goblet cells Brush cells Small granuler cell Basal cells 9 Epithelium of trachea 10 Kartagener sendromu 11 BRONCHIAL TREE & LUNG • Trachea • 2 main bronchus (primary bronchus) • Lobar bronchus (secondary bronchus) • (3 on the right 2 on the left) • Segmental bronchus (tertiary bronchus) • Bronchioles • Terminal bronchioles 12 13 BRONCHIAL TREE • Mucosa – Epithelium – Lamina Propria and Elastic Fibers; • Submucosa • Adventitia in distal bronchi as cells become simple columnar and then cuboidal. 14 • Trachea divide into two primary bronchi • Enter the lung at hilum • Three bronchi in right lung, two in the left lung (lobar bronchi) • Divide and give rise to bronchioles • Branches to form 5-7 terminal bronchioles 15 16 HISTOLOGY OF THE BRONCHI 17 Bronchi • • • • • The mucosa of the larger bronchi is structurally similar to the tracheal mucosa except for the organization of cartilage and smooth muscle 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 which become more prominent in the smaller bronchial branches. Numerous lymphocytes and Lymphatic nodules are found both within the lamina propria and among the epithelial cells. MALT 18 19 STRUCTURE OF INTRAPULMONARY AIRWAYS 20 HISTOLOGY OF THE BRONCHIOLES • Diameter 1mm or less, formed after about the 10th generation of branching • Ciliated pseudostratified colunmar ep, decrease height become ciliated simple columnar or cuboidal ep in terminal bronchioles • bronchioles lack both mucosal glands and cartilage, although dense connective tissue is associated with the smooth muscle • Terminal bronchioles- clara cells: no cilia, secretory granules in apex Secrete proteins that protect bronchiolar lining against oxidative pollutants and inflamation • No cartilage, no glands 21 22 terminal bronchiole The epithelium has clara cells, small mucous cells and ciliated cells, as well as chemosensory brush cells and DNES small granule cells like those of the respiratory epithelium higher in the system. bronchiolar lamina propria still contains elastic fibers and smooth muscle, producing folds in the mucosa. Muscular contraction in both the bronchi and the bronchioles is controlled primarily by nerves of the autonomic nervous system 23 Clara cells • Most numerous in the cuboidal epithelium of terminal bronchioles which have nonciliated, dome-shaped apical ends with secretory granules Functions: 1- Secretion of surfactant lipoproteins and mucins in the fluid layer on the epithelial surface 2- Detoxification of inhaled xenobiotic compounds by enzymes of the SER 3- Secretion of antimicrobial peptides and cytokines for local immune defense 4- In a stem cell subpopulation, injury-induced mitosis for replacement of the other bronchiolar cell types. 24 25 ULTRASTRUCTURE OF BRONCHIOLAR EPITHELIUM: CLARA CELLS 26 HISTOLOGY OF THE RESPIRATORY BRONCHIOLES •Terminal bronchioles subdivide into respiratory bronchioles •Between the conducting and respiratory portion •Wall interrupted by numerous saclike alveoli •Ciliated cuboidal ep with clara cell •Smooth muscle 27 •Elastic connective tissue 28 29 Alveolar duct • Distal ends of respiratory bronchioles branch into tubes called alveolar ducts that are completely lined by the openings of alveoli • Lined with squamous alveolar cells • Thin LP • network of smooth muscle cells surrounds each alveolar openning and a matrix of elastic and collagen fibers supports both the duct and its alveoli, Sphincter like smooth muscle bundles appear as knobs between adjacent alveoli Smooth muscle disappear at the distal end of AD 30 31 • ADs open into atria, that comminicate with alveolar sac (Larger clusters of alveoli called alveolar sacs) • The lamina propria is extremely thin, consisting essentially of a network of elastic and reticular fibers that encircles the alveolar openings and closely surrounds each alveolus • Prominent in this sparse connective tissue, another network of capillaries also surrounds each alveolus. 32 33 Alveoli • Spongy structure of lung, similar to honeycombs • 200µm diameter • Each adult lung has approximately 200 million alveoli with a total internal surface area of 75 m2. 34 • Interalveolar septum consisting of fibroblasts and extracellular matrix (ECM), elastic and reticular fibers, of connective tissue and the richest capillary networks of the body 35 Blood-air barrier 1. Surface lining and cytoplasm of alveolar cells 2. Fused basal lamina 3. Cytoplasm of endothelial cell The total thickness of these layers varies from 0.1 to 1.5 μm. Macrophages and other leukocytes can also be found within the septa Alveolar pores (of Kohn), 10-15 μm in diameter, penetrate the interalveolar septa and connect neighboring alveoli that open to different bronchioles. The pores equalize air pressure in these alveoli and permit collateral circulation of air when a bronchiole is obstructed. 36 • Capillary endothelial cells are extremely thin but continuous and not fenestrated and very thin. Demonstrate highly efficient gas exchange. Ultrastructurally, the most prominent features in the flattened portions of the cell are numerous pinocytotic vesicles. 37 Type I alveolar cells(type I pneumocytes) • • • • • Organelles are grouped around the nucleus, reducing the thickness of the cytoplasm at the blood-air barrier to as little as 25 nm. • Line alveolar surface (95%) maintain the alveolar side of the blood-air barrier Thin 25nm Abundant pinocytotic vesicles – play role in the turnover of surfactant and removal of small particulate contaminants from outer surface Occluding junctions, prevent the leakage of tissue fluid into the alveolar air space Provide a barrier of minimal thickness that is readily permeable to gases 38 Type II alveolar cells (type II pneumocytes) or septal cells • • • • • • • İnterspersed among the type I alveolar cells bound them by Occluding and desmosomal junctions Cuboidal cells Line alveolar wall rest on the same basal lamina and have the same origin as the type I cell Type II cells divide to replace their own population after injury and to provide progenitor cells for the type I cell population Lamellar bodies; contain concentric or parallel lamellae limited by unit membrane (1 to 2 μm in diameter ) Secrete pulmonary surfactant; lowers the alveolar surface tension 39 Alveolar macrophages • Dust cells • Found in alveoli and in the interalveolar septum, often seen on the surface of the alveolus • Phagocytosed debris and erythrocytes lost from damaged capillaries and airborne particulate matter. 40 Regeneration in the Alveolar Lining • Inhalation of toxic gases or similar materials can kill types I and II cells lining pulmonary alveoli. Death of the first cells results in increased mitotic activity in the remaining type II cells • The normal turnover rate of type II cells is estimated to be 1% per day and results in a continuous renewal of both alveolar cells • increased toxic stress, some Clara cells can also be stimulated to divide and give rise to alveolar cells. 41 Pleura • • • • Serous membrane covering the lung two layers: The membrane attached to lung tissue is called the visceral pleura and the membrane lining the thoracic walls is the parietal pleura. The two layers are continuous at the hilum and are both composed of simple squamous mesothelial cells on a thin connective tissue layer containing collagen and elastic fibers. , Pleural cavity between the parietal and visceral layers is lined with mesothelial cells that normally produce a thin film of serous fluid that acts as a lubricant, facilitating the smooth sliding of one surface over the other during respiratory movements. 42 43 44