Lecture13 microscopic structure of the respiratory


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  • Nasal Vestibule is the most anterior part of the nasal cavity . It's enclosed by the cartilages of nose and lined by the same epithelium of the skin (Stratified squamous, keratinized). The other part of the nasal cavity, which is lined by the respiratory epithelium , is called nasal cavity proper . Inside the vestibule are small hairs called vibrissae , which filter dust and other matter that you breath in.
  • Bowman's glands (aka olfactory glands, glands of Bowman) are situated in the olfactory mucosa , beneath the olfactory epithelium , in the lamina propria , a connective tissue also containing fibroblasts, blood vessels, and bundles of fine axons from the olfactory neurons. [1] The structure of the Bowman's glands consists of an acinus in the lamina propria and a secretory duct going out through the olfactory epithelium. Electron microscopy studies show that Bowman's glands contain cells with large secretory vesicles. [2] Bowman's glands might secrete proteins such as Lysozyme , amylase and IgA similarly to serous glands . The exact composition of the secretions from Bowman's glands is unclear, but there is evidence that Bowman's glands do not produce odorant binding protein . [3]
  • P seoduglandular period: All major elements of the organ have formed except those involved with gas exchange (respiratory bronchioles and alveoli) A lveolar period C analicular period T erminal sac period
  • Lecture13 microscopic structure of the respiratory

    1. 1. Lecture 13 ESS_2nd semester <ul><li>Microscopic structure of the respiratory </li></ul><ul><li>system </li></ul><ul><li>N asal cavity, larynx, and trachea </li></ul><ul><li>Histology of the lung and blood-air barrier </li></ul><ul><li>Outline of development of respiratory passages </li></ul><ul><li>and the lung </li></ul>
    2. 2. <ul><li>t he respiratory system (R S ) includes </li></ul><ul><li>lungs and </li></ul><ul><li>a system of tubes </li></ul><ul><li>that links the sites of gas exchange with the external environment </li></ul><ul><li>Main functions of the RS are: </li></ul><ul><li>oxygenation of blood by way of inspired air </li></ul><ul><li>elimination of carbon dioxide (a toxic by-product of body metabolism) by way of expired air </li></ul><ul><li>excretion of water and volatile substances, such as alcohol etc , </li></ul><ul><li>b esides mentioned functions , R S takes part in some specialized functions as </li></ul><ul><li>are </li></ul><ul><li>phonation </li></ul><ul><li>smell </li></ul><ul><li>filtration of inspired air </li></ul>
    3. 3. <ul><li>Respiratory system consists of 2 principal parts: </li></ul><ul><li>1. conducting portion (respiratory passages) </li></ul><ul><li>that involves </li></ul><ul><li>extrapulmonary one - nasal cavity, </li></ul><ul><li>nasopharynx, larynx, trachea and primary </li></ul><ul><li>bronchi </li></ul><ul><li>intrapulmonary one – bronchial tree </li></ul><ul><li>(bronchi, bronchioles, and terminal bronchioles) </li></ul><ul><li>2. respiration portion consisting of: </li></ul><ul><li>respiratory bronchioles </li></ul><ul><li>alveolar ducts and alveoli </li></ul><ul><li>A wall of respiratory passages </li></ul><ul><li>is rigid and prevents collapse lumen of the conducting portion </li></ul><ul><li>is composed of 3 layers </li></ul><ul><li>mucosa - cover s the luminal surface and consists of pseudostratified ciliated columnar epithelium with mucous goblet cells and thin lamina propria </li></ul><ul><li>fibrocartilaginous layer - support s the walls, being composed of hyaline, and elastic cartilages and bundles of smooth muscle tissue (caudally and dorsally) </li></ul><ul><li>adventitia - loosely connects both previous layers with surroundings </li></ul><ul><li>is composed of loose connective tissue with blood vessels and nerve bundles </li></ul>
    4. 5. <ul><li>Nasal cavity </li></ul><ul><li>- is divided by a midline nasal septum into right and left part - nasal fossae, </li></ul><ul><li>- both fossae communicates with the exterior through the nares (nostrils), with the nasopharynx through the posterior nares </li></ul><ul><li>each nasal cavity comprises </li></ul><ul><li>vestibule </li></ul><ul><li>respiratory portion (area) and </li></ul><ul><li>olfactory portion (area) </li></ul>Vestibule - narrow zone in which the epidermis from external surface of the nose is replaced by nonkeratinized pseudostratified columnar epithelium a round the inner surface of the nares are large sebaceous and sweat glands bound to thick and short hair called vibrissae they filter out large particles from the inspired air
    5. 6. <ul><li>Respiratory area ( portion) </li></ul><ul><li>- is lined with pseudostratified ciliated columnar epithelium with goblet cells </li></ul><ul><li>- a lamina propria containing seromucous glands </li></ul><ul><li>it grows deeply together with the periosteum or perichondrium of bone or c artilage </li></ul><ul><li>t hree bony shelf-like projections called conchae protrude into both nasal fossae from the lateral wall of the </li></ul><ul><li>nasal septum </li></ul><ul><li>t he superior concha belongs to the olfactory portion </li></ul><ul><li>the middle and inferior conchae contain a rich vascular plexus (mainly in inferior conchae) that serves to warm </li></ul><ul><li>of inspired air (conditioning of the inspired air) – (They also produce turbulence of the air so that the contact surface with mucosa becomes greater and thereby increasing the humidity!) </li></ul><ul><li>Olfactory area ( portion) </li></ul><ul><li>occupies the roof of each nasal fossa (regio olfactoria)it is lined with olfactory mucosa that contains the receptors for the sense of smell (sensory cells-unipolar!) </li></ul><ul><li>cells are modified bipolar neurons – they have dilated apex with nonmotile cilia and axon (BOWMANS GLANDS) </li></ul>
    6. 7. <ul><li>Paranasal sinuses </li></ul><ul><li>are air-filled cavities within the bones of the skull (maxillary, frontal, ethmoid and </li></ul><ul><li>sphenoid), which communicate through small openings with the nasal cavities </li></ul><ul><li>they are lined with the same but thinner mucosa (periost + lamina p ropria + </li></ul><ul><li>epithelium) as the respiratory portion of nasal fossae </li></ul><ul><li>The nasopharynx </li></ul><ul><li>is upper part of the pharynx which </li></ul><ul><li>- anteriorly is open into the nasal cavity through posterior nares,choana! </li></ul><ul><li>- posteriorly and laterally is surrounded by the muscular tissue </li></ul><ul><li>- caudally is continued with the oropharynx and larynx </li></ul><ul><li>t he epithelium of the pharynx is pseudostratified ciliated columnar with goblet cells </li></ul><ul><li>s mall glands (mucous, serous and mixed) and accumulations of lymphatic tissue </li></ul><ul><li>(pharyngeal tonsil - posteriorly, tubal tonsils - laterally) are in the lamina propria </li></ul><ul><li>th e middle layer of the pharynx is of muscular character being formed by bundles of </li></ul><ul><li>the striated muscles </li></ul>
    7. 8. <ul><li>Larynx C3-C6 </li></ul><ul><li>is an irregular tube connecting pharynx and trachea </li></ul><ul><li>th e skeleton of the organ is formed large hyaline (thyroid, cricoid, and most of the arytaenoid) and small elastic (epiglottis, cuneiform and corniculate) cartilages that are bound together by ligaments + membranes. </li></ul><ul><li>s triated skeletal muscles insert to the surface of cartilages and provide to move against each other </li></ul><ul><li>i nner surface is covered by the mucosa consisting of dense connective tissue with seromucous glands and the islets of lymphatic tissue </li></ul><ul><li>e xcept two sites, the entire larynx is lined with pseudostratified ciliated columnar epithelium w ith goblet cells </li></ul><ul><li>b elow the aditus , the mucosa forms 2 pairs of folds that extend into the lumen of the larynx </li></ul><ul><li>the upper pair constitutes the false vocal cords , covered by typical pseudostratified columnar epithelium; </li></ul><ul><li>the lower pair of folds constitutes true vocal cords that are covered by stratified squamous epithelium </li></ul>b etween folds the sinus and saccule of the larynx a small slit-like diverticulum of laryngeal cavity is located on each side
    8. 9. <ul><li>True vocal cords : </li></ul><ul><li>- stratified squamous epithelium, </li></ul><ul><li>- lamina propria (loose fibroconnective tissue), </li></ul><ul><li>- ligamentum vocale (elastic connective tissue), </li></ul><ul><li>- musculus thyreoarytaenoideus (cross-striated muscle tissue </li></ul><ul><li>lying in plica vocalis outer to ligamentum) </li></ul><ul><li>False vocal cords : </li></ul><ul><li>- pseudostratified ciliated columnar epithelium + goblet cells </li></ul><ul><li>- lamina propria of mucosa with mixed glands </li></ul><ul><li>t he shape of the opening between the vocal cords (the glottis) varies with </li></ul><ul><li>breathing and phonation </li></ul>
    9. 10. The epiglottis closes aditus into the larynx basic tissue of the organ is elastic cartilage i t is covered with a mucous coat: stratified squamous epithelium is on its lingual aspect while pseudostratified columnar epithelium is on the laryngeal surface t he mucosa contains mixed serous and mucous glands
    10. 11. <ul><li>Trachea </li></ul><ul><li>is a tube about 10-12 cm long, 2-2.5 cm in </li></ul><ul><li>diameter </li></ul><ul><li>Mucosa: (inner side) </li></ul><ul><li>- pseudostratified ciliated columnar epithelium + </li></ul><ul><li>goblet cells </li></ul><ul><li>- lamina propria mucosae (thin layer of connective </li></ul><ul><li>tissue (with elastic fibers, </li></ul><ul><li>it contains islets of lymphatic tissue) </li></ul><ul><li>Submucosa: layer of loose connective tissue with </li></ul><ul><li>small mixed glands </li></ul><ul><li>Fibrocartilaginous layer: C-shaped hyaline </li></ul><ul><li>cartilages (l6-20) + (annular lig.) , posteriorly free ends are connected by ligaments (X, Y-shaped), </li></ul><ul><li>musculus trachealis is present in posterior part of </li></ul><ul><li>the tracheal wall </li></ul><ul><li>Adventitia: loose connective tissue with blood </li></ul><ul><li>vessels and nerves </li></ul><ul><li>it connects the trachea with surrounding structures </li></ul><ul><li>similar structure as trachea show the primary or </li></ul><ul><li>extrapulmonary bronchi </li></ul>
    11. 12. <ul><li>Lungs ( L at. pulmo, Greek pneumón) </li></ul><ul><li>a re located in the pleural cavity lined by </li></ul><ul><li>parietal pleura , which is to come over the </li></ul><ul><li>lungas the visceral pleura (mesothelium </li></ul><ul><li>+ thin layer of dense connective tissue) at </li></ul><ul><li>the hilum of each lung </li></ul><ul><li>t he pleural cavity contains a small amount </li></ul><ul><li>of watery, serous fluid </li></ul><ul><li>The bronchial tree </li></ul><ul><li>primary bronchi (extrapulmonary) enter the </li></ul><ul><li>right and left lung </li></ul><ul><li>they divide in secondary bronchi (3 in the </li></ul><ul><li>right, 2 in the left that supply pulmonary </li></ul><ul><li>lobes </li></ul><ul><li>secondary or lobar bronchi divide into </li></ul><ul><li>tertiary bronchi supplying b roncho - </li></ul><ul><li>pulmonary segments (anatomical units </li></ul><ul><li>of the structure) </li></ul><ul><li>t he tertiary bronchi repeatedly divide, at </li></ul><ul><li>minimal 10 times, so that small bronchi of </li></ul><ul><li>12 orders arise </li></ul><ul><li>these are called bronchioles and conduct </li></ul><ul><li>air into pulmonary lobules </li></ul>
    12. 13. <ul><li>bronchioles are the last of intrapulmonary bronchi that contain cartilage in their wall </li></ul><ul><li>in general, the structure of primary bronchi is similar to the trachea </li></ul><ul><li>p roceeding toward the respiratory portion, a simplification of histologic </li></ul><ul><li>organization of both epithelium and underlying lamina propria is </li></ul><ul><li>observed </li></ul><ul><li>i t must be emphasized that the simplification is gradual, and no abrupt transition </li></ul><ul><li>can be observed between the bronchi and bronchioles </li></ul><ul><li>P ulmonary lobule </li></ul><ul><li>t he unit of structure of the lung is called the pulmonary lobule </li></ul><ul><li>there is a part of the lung parenchyma of pyramidal shape (apex of the pyramid is </li></ul><ul><li>directed toward the hilum of the lung) </li></ul><ul><li>at the apex; bronchiole and the branch of pulmonary artery enter the l obule </li></ul><ul><li>t he branches of pulmonary vein (with oxygenate blood) run in the connective tissue </li></ul><ul><li>of interlobular septa, which delineate adjacent l obules </li></ul><ul><li>i nterlobular septa contain also lymphatic vessels </li></ul>
    13. 14. <ul><li>Pulmonary lobule </li></ul><ul><li>air is conducted to it by </li></ul><ul><li>bronchiole </li></ul><ul><li>each bronchioles divides into </li></ul><ul><li>5 - 7 terminal bronchioles </li></ul><ul><li>e ach terminal bronchiole </li></ul><ul><li>subdivides into 2 or more </li></ul><ul><li>respiratory bronchioles </li></ul><ul><li>that are sites of transition between the conducting and respiratory portions of RS </li></ul><ul><li>r espiratory bronchioles pass </li></ul><ul><li>into </li></ul><ul><li>alveolar ducts and sacs </li></ul><ul><li>and these into </li></ul><ul><li>alveoli </li></ul>
    14. 16. <ul><li>ALVEOLI (alveoli pulmonum) </li></ul><ul><li>- have diameter 100 – 300  m </li></ul><ul><li>- number of alveoli is cca 300 - </li></ul><ul><li>5 00 mil lions </li></ul><ul><li>- they occupy surface area of 80 - 120 </li></ul><ul><li>m 2 </li></ul><ul><li>- are polyhedral or hexagonal and </li></ul><ul><li>separated by a thin interalveolar sept ae </li></ul><ul><li>- the septum consists of interstitium </li></ul><ul><li>(connective tissue with elastic and </li></ul><ul><li>reticular fibers and different cell types </li></ul><ul><li>(fibroblasts, mono- and lymphocytes, </li></ul><ul><li>alveolar macrophages) and blood </li></ul><ul><li>capillaries </li></ul><ul><li>- both si des of septae are covered with </li></ul><ul><li>respiratory epithelium on basal lamina </li></ul><ul><li>- interalveolar pores occur in the wall </li></ul><ul><li>of alveoli and are important for </li></ul><ul><li>collateral circulation </li></ul>
    15. 17. <ul><li>Respira tory epit h el ium </li></ul><ul><li>the type I alveolar cell s or membranous pneumocyte s - flattened, with micropino - </li></ul><ul><li>cytotic vesicles near basal and apical surfaces and thin processes ( 20–25 nm ), cells cover cca </li></ul><ul><li>97 % of the alveolar surface </li></ul><ul><li>the type II alveolar cell s or granular pneumocyte s - cuboidal cell s with secretory </li></ul><ul><li>granules in the cytoplasm ; they contain phospholipid- </li></ul><ul><li>protein and are secreted on the surface of </li></ul><ul><li>epithelium as monomolecular film &quot;lining </li></ul><ul><li>complex&quot; (surfactant) that is primarily </li></ul><ul><li>composed of dipalmitoyl lecithin </li></ul><ul><li>t he layer of surfactant (about 30 nm thick) </li></ul><ul><li>prevents from atelectasis (alveolar collapse) </li></ul><ul><li>lamina basalis </li></ul>
    16. 19. Alveolar macrophages: occur w ithin the alveoli or in the septa e cells are movable and able to phagocyte inspired particles of dust etc. they form a part of phagocyte macrophages system
    17. 20. Blood-air barrier consists of: 1- respiratory epithelium with surfactant on the surface , 2- the basal laminae of closely apposed alveolar and endothelial cells, 3- endothelial cells of blood capillaries of continuous type t he total thickness of these layers varies from 0.1 to 1.5  m i nsufficient surfactant production causes difficulty in expanding alveoli and injury of the respiratory epithelium in premature new-borns t he disease - respiratory distress syndrome g lucocorticoids stimulate the synthesis of surfactant and are used in treatment of the Respiratory Distress Syndrome (RDS).
    18. 21. <ul><li>TRACHEA </li></ul><ul><li>p seudostr atified cil iated column ar ep. with goblet cells </li></ul><ul><li>^ </li></ul><ul><li>right - PRIMARY BRONCHI - left </li></ul><ul><li>(the same ep ithelium ) </li></ul><ul><li>^ </li></ul><ul><li>3 - SECONDARY BRONCHI - 2 </li></ul><ul><li>(LOBAR) </li></ul><ul><li>LOBES </li></ul><ul><li>(the same ep ithelium) </li></ul><ul><li>^ </li></ul><ul><li>l0 - TERTIARY BRONCHI - 8 </li></ul><ul><li>(SEGMENTAL) </li></ul><ul><li>(the same ep ithelium) </li></ul><ul><li>SEGMENTS </li></ul><ul><li>^ </li></ul><ul><li>BRONCHIOLES (of 12 order) </li></ul><ul><li>(ciliated columnar ep.) 1 mm in diameter </li></ul><ul><li>PULMONARY LOBULES </li></ul><ul><li>^ </li></ul>^ TERMINAL BRONCHIOLES (simple ciliated columnar - cuboidal ep.) 0.5 mm in diameter lamina propria is composed largely of smooth muscle and elastic fibers ^ RESPIRATORY BRONCHIOLES (cuboidal- squamous ep.)<0.3 mm in diameter, wall is interrupted by more or less numerous alveoli where gas exchange occurs smooth muscle and elastic connective tissue lie beneath the epithelium ^ ALVEOLAR DUCTS is a part of tree whose wall protrude in individual alveoli A.d. open into atria that communicate with alveolar sacs (2 or more of which arise from each atrium ^ ALVEOLAR SACS AND ALVEOLI respiratory ep. with two cell types The bronchial tree
    19. 22. <ul><li>Pleura </li></ul><ul><li>pleura parietalis </li></ul><ul><li>pleura visceralis </li></ul><ul><li>is composed of simple squamous epithelium (mesothelium) and thin layer of connective tussue ( 1 mm) </li></ul><ul><li>Blood supply of the lungs </li></ul><ul><li>t wo blood circulations are distinguished in the lungs: functional and nutritive ones </li></ul><ul><li>F un ctional circulation : t runcus pulmonalis < into right and left pulmonary artery < their branches </li></ul><ul><li>(follow respir. tree) < capillary network around alveoli > venules (collect the blood rich in </li></ul><ul><li>oxygen) > venules and veins in interlobular connective tissue (septa) > vv. pulmonales </li></ul><ul><li>Nutritive circulation : b ronchial arteries (the branches of aorta or intercostal arteries) - follow the bronchi, </li></ul><ul><li>run in interlobular connective tissue and in pleura - return through vv. pulmonales into the heart </li></ul>
    20. 23. <ul><li>Outline of development of respiratory passages and the lung </li></ul><ul><li>t he low part of respiratory system (from larynx downstairs) develops as an outgrowth of the ventral wall of the foregut </li></ul><ul><li>as t he wall of entire gut is lined by the endoderm the epithelial lining of conducting as well as respiratory portions is of endodermal origin </li></ul><ul><li>t he cartilaginous and muscular components of the trachea and lungs derive </li></ul><ul><li>from the mesenchyma (from the splanchnic mesoderm) </li></ul><ul><li>i nitial stage of development </li></ul><ul><li>is called as the respiratory </li></ul><ul><li>diverticulum </li></ul><ul><li>it occurs in the caudal end </li></ul><ul><li>of the ventral wall of the </li></ul><ul><li>pharynx when the embryo </li></ul><ul><li>is aged 26 to 27 days </li></ul>
    21. 24. <ul><li>t he diverticulum then expands in caudal direction and it becomes separated from the foregut by the development of two longitudinal esophagotracheal ridges (folds) </li></ul><ul><li>the ridges subsequently fuse to form a septum – esophagotracheal septum </li></ul><ul><li>the foregut is divided in </li></ul><ul><li>a dorsal portion, the esophagus , and a ventral portion, the trachea and lung bud </li></ul><ul><li>t he site where the trachea communicates with the pharynx is called laryngeal </li></ul><ul><li>Orifice, between 5 th and 6 th pharyngeal arches. </li></ul>
    22. 25. 4. The FOURTH – SIXTH. Cartilage – cartilages of larynx and trachea. Mesenchyme – cricothyroid, levator veli palatini, constrictors of pharynx, intrisic muscle from larynx. The 4th aortic arch – has the ultimate fate different on the left and right sides, On the left it forms a part of the arch of the aorta between the left common carotid artery and the left subclavian vein. On the right side the proximal segment of the right subclavian artery. The 5th aortic arch - is transient and soon obliterates. The 6th aortic arch – transform into pulmonary artery (their branches) Branchial nerves – Superior laryngeal branch of the vagus, recurrent laryngeal branch of the vagus.
    23. 26. <ul><li>a lung bud soon divides into two knob-like bronchial buds </li></ul><ul><li>e arly in the fifth week , each bronchial bud enlarges to form a primitive </li></ul><ul><li>primary bronchus </li></ul><ul><li>c oncurrently, the primary bronchi subdivide into secondary bronchi (on </li></ul><ul><li>the right 3, on the left 2) that will supply future lobes </li></ul><ul><li>e ach secondary bronchus subsequently undergoes dichotomous branching; </li></ul><ul><li>the branches are called the tertiary or segmental bronchi (supply </li></ul><ul><li>bronchopulmonary segments) - 10 in the right, 8 or 9 in the left (7th week) </li></ul><ul><li>The 24 weeks , about 17 orders of branches have formed and the respiratory </li></ul><ul><li>bronchioles are present </li></ul>
    24. 27. <ul><li>w ith subsequent growth in caudal and lateral directions, the lung buds penetrate into primitive pleural cavities </li></ul><ul><li>the mesoderm, which covers the outside of the lung, develops into the visceral pleura </li></ul><ul><li>t he somatic mesoderm layer, covering the body wall from the inside, becomes the parietal pleura </li></ul><ul><li>t he space between the parietal and visceral pleura is the pleural cavity </li></ul>
    25. 28. <ul><li>d uring development of the lungs , the endodermal lining thins so that the barrier </li></ul><ul><li>between the blood vessels in the mesenchyma and the air that will fill the lungs at </li></ul><ul><li>birth is as slight as possible (BLOOD-AIR BARRIER) </li></ul><ul><li>t his continuous process is conventionally divided up into four general periods that </li></ul><ul><li>overlap because differentiation is usually more advanced in the cranial part of the </li></ul><ul><li>lungs than caudally </li></ul>periods: Pseudoglandular period - lung s somewhat resemble of a gland , at the end; all major elements of the organ have formed except those involved with gas exchange (respiratory bronchioles and alveoli) e ndoderm cells are cuboidal
    26. 29. <ul><li>Canalicular period - vascularization begins and the respiratory bronchioles are developed, at the ends of some respiratory bronchioles thin-walled terminal sacs may be seen </li></ul><ul><li>s urvival of the fetus is unlikely at this time </li></ul><ul><li>Terminal sac period = primitive alveoli period - the development of terminal sacs continues, capillaries come into close contact with the epithelium of primitive alveoli, type I alveolar epithelial cells are already differentiate , p roduction of pulmonary surfactant begins </li></ul><ul><li>a fter 28 weeks survival of the fetus is possible </li></ul>
    27. 30. Alveolar period - is characterized by differentiation of terminal sacs into the future alveolar ducts
    28. 31. <ul><li>Malformations of the respiratory system </li></ul><ul><li>Lung agenesis - lung buds fail to form, unilateral or bilateral, survival is possible in unilateral form (compensation by the remaining lung) </li></ul><ul><li>bilateral agenesis is fatal </li></ul><ul><li>Respiratory distress syndrome - inadequate production of surfactant in premature babies </li></ul><ul><li>t he lungs may therefore collapse and the endoderm cell surface may be damaged </li></ul><ul><li>Tracheo-esophageal fistula - situation when the trachea and gut were to come into contact - </li></ul><ul><li>i t is commonnly associated with esophageal atresia - blind ending of the gut - incidence is 1 per 3 , 000 - 4,500 births </li></ul>
    29. 32. <ul><li>clinical finds: </li></ul><ul><li>t he new-born baby will gag as its saliva enters its lungs and shows signs of respiratory distress </li></ul><ul><li>m ilk may be regurgitated on feeding </li></ul><ul><li>w hen the child cries , its abdomen may become distended as air is drawn into the stomach </li></ul>