Please enable JavaScript.
Coggle requires JavaScript to display documents.
Microanatomy of Respiratory System (Order (Nasal cavities, Pharynx, Larynx…
Microanatomy of Respiratory System
Order
Nasal cavities
Pharynx
Larynx
Paired main Bronchi
Terminal Bronchioles
Bronchioles
Respiratory bronchioles
Alveolar ducts > sacs > alveoli
Trachea
Conductive portion (airways)
Nasal Cavities
pseudostratified columnar epithelium containing cell bodies of bipolar nerve (olfactory) cells
Cilia contain proteins that act as odorant receptors
Tubuloalveolar olfactory glands that secretes proteinaceous substance
Keeps surface moist and trap odiferous substances
Pharynx
Mucous glands
Lined distally by stratified squamous epithelium, continuous with this type at proximal end of larynx
Larynx
elongated, irregularly shaped structure
Lined by stratified squamous epithelium at proximal end, ciliated pseudostratified column at its distal end
Wall contains hyaline and elastic cartilage, CT, elastic tissue, skeletal muscle and mucosal glands
Tension in large mucosal folds (vocal cords) and size of luminal opening regulated by contraction of skeletal muscle (determines pitch)
Trachea, bronchi and bronchioles
Acinus: portion of lung parenchyma distal to terminal bronchiole, principal anatomical unit involved in gas exchange
Pulmonary arteries closely follow bifurcating airways in central portions of acini and lobules
Pulmonary veins located in CT septa and drains adjacent lobules
Terminal bronchiole ends at about 16th gen, following which is respiratory bronchioles
8 types of cells
Ciliated cells (cilia + cilia beating)
Goblet (mucous) cells
Stains palely in H&E
nucleus located near base of cell
Contribute to mucus secretion
Basal cells
round nuclei, close to base
Give pseudostratified appearance
Reserve progenitor population for ciliated and mucous cells
Bronchiolar exocrine secretary cells
Non-ciliated columnar excrine epithelial cells found in bronchioles in humans
Prominent RER, GA, secretory granules, characterized by DOME shape
Brush cells
Found in trachea and bronchi
Dense core granule cells
Triangular, basally located secretory granules, touch basal lamina
Serous cells
Found predominantly in trachea and bronchi
round nuclei, abundant RER and dense apical secretory granules
Secrete glycoproteins and lysozymes
decrease viscosity (due to its low viscosity)
intermediate
non-ciliated columnar cells that are immature, replace cells
goblet or ciliated cells
Epithelial transitions
Ciliated cells undergo gradual reduction in height
trachea (psuedostratified ciliated columnar)
Bronchi (Simple columnar ciliated)
Bronchioles (simple squamous non-keratinized)
Submucosal glands (mucous and serous) decrease in no. in distal bronchi, and not found in bronchioles
Goblet cells increase in no. as submucosal glands decrease, present throughout bronchi
Exocrine secretory cells (dome shaped) is major secretory cell in bronchioles
Layers of tracheal wall
Mucosa
Epithelial cells with unusually thick basal laminar
Laminar propria (containing cellular CT, high elastin content, contains lymphocytes and lymphatic nodules)
elastin from laminar propria extend longitudinally from trachea to terminal bronchioles, contiguous with alveolar elastic tissues
Submucosa
Dense CT containing cartilage (c shaped) and sero-mucous glands (with ducts that pierce up to epithelial cells)
Down the trachea (to bronchi) cartilaginous rings give way to less regular plates in large and medium bronchi, and isolated fragments in small bronchi
Adventitia
DICT that blends with surrounding CT
Muscularis
Smooth muscle between ends of cartilage
encircles lumen of bronchi and large bronchioles
progressively thins in bronchioles and terminates in alveolar ducts
Bundles are spirally interlaced so contraction leads to airway narrowing
Functional aspects
watery hypophase covers epithelial cell apices and overlaid by an incomplete viscous mucus blanked that traps foreign material and prevent cellular druing
Cilia beats in hypophase, propelling inner mucus layer upwards towards trachea to remove materials
Respiratory portion
Terminal bronchiole (from conducting) > respiratory bronchioles > alveoli in some parts / alveolar ducts > alveolar sacs > alveoli
Markedly thinned epithelial cells of alveolar septum, with rich capillary network immediately beneath epithelium
Alveolar septa supported by elastic connective tissue fibers, anchored to both axial (airway) and visceral pleural CT
5 types of cells
Alveolar Type I (squamous alveolar epithelial cells)
Site of gas exchange, flattened cytoplasm
Alveolar Type II
Rounded cuboidal cells form tight junctions with Type I
Positioned in alveolar corners and alveolar septal junctions
secretory function with granular ER, golgi complexes, multivesicular bodies and prominent lamellar bodies
Lamellar bodies bring lipid to lumen, delivering pulmonary surfactant to surface of lumen
Contains phospholipids and surfactant proteins A, B, C and D that aid in the spreading of surfactant on the alveolar surface, and are involved in lung defense
Also stem cell for alveolar epithelium, impt in regeneration after injury
capillary endothelial cell
Alveolar macrophages
Wander freely in alveoli
Located in aqueous hypophase of surfactant layer, move over the alveolar surface ingesting microorganisms
Display prominent vesicles, phagosomes, multivesicular bodies, lysosomes, and mitochondria
Interstital cells
Primarily fibroblasts
Alveolar septal CT consist of fine elastic fibers and bundles of collagen fibrils, derived from fibroblasts, providing support for capillary network
Functional aspect
Interstital elastic fibers help provide support on alternate sides of capillaries in alveolar septum
Results in thick and thin portions of alveolar septum
Side of septum devoid of fibers is thinned to two cell layers, separated by fused basal laminae
Minimal thickness = optimal gas exchange
Absence of interstital space prevents accumulation of interstital fluid
2-part lining flim smooths capillary bulge into alveoli through a liquid hypophase that fills pits, and a thin phospholipid layer on free surface to decrease surface tension
Communications between adjacent alveoli normally present as small round openings in alveolar septum (pores of kohn)
Impt in providing alternate routes of airflow when airways are obstructed
Vasculature
Primary venous drainage of both pulmonary and bronchial arterial systems are via pulmonary veins to left atrium
Bronchial veins, which return venous blood from proximal airways to the azygos and hemiazygos venous systems, are a minor component of total venous return from the lung
Lymphatics: drain into para-alveolar lymphatics (fine lymphatic vessels) in connective tissue septa in bronchi and bronchioles
Nerves
Innervated by sympathetic and parasympathetic fibers of autonomic nervous and be visceral afferent nerves
Primary effectors are bronchial and bronchiolar smooth muscle