Anatomy, physiology and pathology of the respiratory system (“but mainly the lungs”) - PowerPoint PPT Presentation

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Anatomy, physiology and pathology of the respiratory system (“but mainly the lungs”)
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Anatomy, physiology and pathology of the respiratory system (“but mainly the lungs”)

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  1. Anatomy, physiology and pathology of the respiratory system (“but mainly the lungs”) Dr Andrew Potter Registrar Department of Radiation Oncology Royal Adelaide Hospital

  2. Anatomy

  3. Overview • Consists of nose, pharynx, larynx, trachea, bronchi, lungs • Conducting portion and respiratory portion • Obtains O2 and eliminates CO2 to external environment • Helps regulate pH by adjusting rate of removal of acid-forming CO2

  4. Nose • External portion • Bone and cartilage, covered by skin • Mucous membrane lining • Nostrils, midline septum • Internal portion • Skull cavity inferior to cranium, superior to mouth • Bounded by ethmoids, maxillae, palatine bone, inferior nasal conchae • Communicates with pharynx through the choanae • Communicates with paranasal sinuses • frontal, sphenoid, maxillary, ethmoid • Openings of naso-lacrimal ducts, Eustachian tubes

  5. Pharynx (throat) • Funnel-shaped tube, ~13cm long • Starts at choanae (internal nares) extending to level of cricoid cartilage • Posterior to nasal cavity, oral cavity, larynx • Anterior to cervical vertebral bodies • Muscular wall lined by mucous membrane

  6. Nasopharynx • Uppermost part of pharynx • Posterior to nasal cavity • Extends to plane of soft palate • Eustachian tube openings • Allows air exchange to equalise ear/nose/throat pressures • Pharyngeal tonsils (adenoids) on post wall

  7. Oropharynx • Posterior to oral cavity • Extends from soft palate to level of hyoid • Common passage way for air, food, fluid - communicates with oral cavity • Palatine and lingual tonsils

  8. Hypopharynx (laryngopharynx) • Extends downwards from hyoid • Continuous with oesophagus (posteriorly) and larynx (anteriorly) • Common passage way for air and food

  9. Larynx (voice box) • Connects pharynx with trachea • Epiglottis • cartilage valve to separate food and air • Midline in neck, anterior to C4-C6 • Wall consists of 9 pieces of cartilage • 3 single • Thyroid, epiglottis and cricoid • 3 paired • Arytenoid, corniculate, cuneiform • Vocal cords - false (ventricular) and true • Vibration of vocal cords results in phonation • Barrier against foreign bodies entering lower respiratory tract

  10. Upper respiratory tract - summary • System of interconnected spaces • Transports, filters, humidifies and warms inspired air • Receptors for smell in the nasal cavity • Paranasal sinuses act as resonating chambers for speech • Also reduce weight of facial skeleton

  11. Trachea • Tubular air passage way ~12cm long, 2.5cm diameter • Anterior to oesophagus • Extends from larynx (cricoid cartilage) to ~T5 • Bifurcation at T5 (carina)into left and right main bronchi

  12. Trachea • 16-20 incomplete ‘C’-shaped hyaline cartilage rings provide rigidity • Open part of each ring faces posteriorly to oesophagus • Allows for oesophageal expansion during swallowing • Transverse smooth muscle (trachealis) and elastic connective tissue attach open ends of cartilage rings

  13. Trachea • Important relations • Anteriorly: thyroid isthmus, inferior thyroid veins, sternohyoid and sternothyroid muscles, manubrium, thymus remnants • Laterally: lobe of thyroid, carotid sheath, SVC (right), aortic arch and branches (left), • Posteriorly: oesophagus, recurrent laryngeal nerves

  14. Trachea • Ciliated pseudo-stratified columnar epithelium • Seromucous glands and ducts • humidify air • Cilia (‘brush border’) • Transport excess mucus, foreign bodies upwards like an escalator

  15. Primary (main) bronchi • Incomplete cartilage rings • Stratified columnar epithelium as in trachea • Right main bronchus • To right lung • Shorter, wider and more vertical than left • More prone to foreign bodies lodging • Left main bronchus • To left lung

  16. Secondary (lobar) bronchi • One for each lobe of each lung • 2 on the left • 3 on the right • Further division into tertiary (segmental) bronchi to supply each segment of each lobe • …progressive branching until reaching bronchioles and finally terminal bronchioles and alveolar ducts

  17. Structural features • Gradual transition from one type of airway to the next • Epithelium • Tall, pseudostratified columnar ciliated epithelium in larynx and trachea • Simple cuboidal non-ciliated in small airways • Goblet cells (mucus secreting) gradually disappear

  18. Structural features • Lymphoid aggregates (MALT) • Produces IgA antibodies secreted onto mucosal surface • protection against invading micro-organisms • Smooth muscle • Lies deep to mucosa (except in trachea) • Becomes increasingly important as airway diameter decreases • Regulates calibre of airway and hence resistance to air flow • Sympathetic - muscle relaxation • Parasympathetic - constriction

  19. Structural features • Serous and mucous glands • Progressively less numerous in narrower airways • Cartilage • Supporting skeleton for larynx, trachea and bronchi • Maintains patency during respiration • Gradually diminishes; absent beyond tertiary bronchi

  20. Lungs - gross anatomy • Paired, cone-shaped organs in thoracic cavity • Separated by heart and other mediastinal structures • Covered by pleura • Fibrous membrane with overlying flattened epithelium • Outer layer - parietal pleura, attached to chest wall • Inner layer - visceral pleural, attached to lung surface • Potential space between the two layers (pleural cavity) • Normally contains small amount of pleural fluid - reduces friction between surfaces during movement of respiration

  21. Lungs - gross anatomy • Extend from diaphragm inferiorly to just above clavicles superiorly • Lies against thoracic cage (pleura, muscles, ribs) anteriorly, laterally and posteriorly • Inferior lung base is concave and fits over convexity of each hemi-diaphragm • Narrow superior apex • Surface curved to match curvature of rib cage

  22. Lungs - gross anatomy • Hilum • Medial ‘root’ of the lung • Point at which vessels, airways and lymphatics enter and exit • Cardiac notch • Lies in medial part of left lung to accommodate the heart

  23. Lobes and fissures • Lungs divided into lobes by fissures • Both have an oblique fissure extending forwards and downwards • Separates upper and lower lobes on left • Separates upper, middle and lower lobes on right • Right lung also has horizontal fissure • Separates upper and middle lobes • Each lobe has its own secondary (lobar) bronchus • Named according to the lobe supplied • Further subdivision of each lobe into segments • …similarly supplied by a tertiary (segmental) bronchus

  24. Lobules • Each segment has multiple small compartments - lobules • Each wrapped in connective tissue • Contains lymphatic vessel, arteriole, venule, branch from terminal bronchiole • Terminal bronchioles subdivide into microscopic respiratory bronchioles

  25. Alveoli • Cup-shaped outpouchings • Clustered in alveolar sacs • Resemble microscopic bunches of grapes • Lined by epithelium • Thin elastic basement membrane • Lined by type I alveolar cells with occasional type II alveolar cells • Type II cells secrete alveolar fluid and surfactant • Surfactant acts to reduce surface tension of alveolar fluid (like detergent), helping to keep alveoli from snapping shut

  26. Alveoli • Alveolar macrophages (dust cells) • Phagocytes that remove dust and debris from alveolar spaces • Derived from peripheral blood monocytes • Alveoli surrounded by capillary network to facilitate gas exchange • Single layer of endothelium and basement membrane

  27. Alveolar-capillary membrane • Diffusion of gas between air and circulation occurs across alveolar and capillary walls • Type I and II alveolar cells • Epithelial basement membrane beneath alveolar wall • Capillary basement membrane • Capillary endothelium • Total thickness ~0.5µm • Approx 300 million alveoli in normal lung • Results in large surface area (~70m2) for gas exchange

  28. Alveoli

  29. Alveoli - micro

  30. Lung - blood supply • Dual supply • Bronchial supply • Bronchial arteries supply bronchi, airway airway walls and pleura • Pulmonary supply • Pulmonary arteries enter at hila and branch with airways • Deoxygenated blood from right ventricle  pulmonary trunk  left and right pulmonary arteries  arterioles  capillaries  oxygenated blood tovenules  pulmonary veins  left atrium • Venous return is common (ie. both return via pulmonary veins)

  31. Lymphatics • Lymphatic drainage follows vessels • Parabronchial (peribronchial) lymphatics and nodes  hilar nodes  mediastinal nodes  pre- and para-tracheal nodes  supraclavicular nodes

  32. Physiology

  33. Mechanics of breathing • Inspiration - an active process • Diaphragm lowers • Ribs pivot upwards • Intercostal muscles contract • Action similar to a swinging bucket handle • Intra-thoracic pressure lowers • Intrapleural pressure is normally 4mmHg lower than atmospheric pressure, ‘sucking’ the lungs outwards • Lung expands • As volume increases, pressure decreases - Boyle’s law • Air flows from higher atmospheric pressure (760mmHg) into low pressure of the lungs (758mmHg)

  34. Mechanics of breathing • Expiration - passive • Inspiratory muscles relax • Ribs move downwards • Diaphragm relaxes and its domes rise • Surface tension of alveolar fluid causes an inward pull • Elastic recoil of alveolar basement membranes • Reverse pressure gradient • 762mmHg in lungs, 760mmHg atmospheric • Gas pushed out

  35. Respiration • External (pulmonary) respiration • exchange of O2 and CO2 between respiratory surfaces and the blood (breathing) • Internal respiration • exchange of O2 and CO2 between the blood and cells • Cellular respiration • process by which cells use O2 to produce ATP

  36. External respiration • Exchange of O2 and CO2 between alveoli and blood • Partial pressure of O2 higher in alveoli (105mmHg) than blood (40mmHg) so O2 diffuses into blood • Partial pressure of CO2 higher in blood (45mmHg) than alveoli (40mmHg), so CO2 moves into alveoli in opposite direction and gets exhaled out

  37. Gas partial pressures

  38. Internal respiration • Exchange of O2 and CO2 between blood and tissues • Pressure of O2 higher in blood than tissues so O2 gets release into tissues. • Pressure of CO2 higher in tissue than in blood so CO2 diffused in opposite direction into blood. • CO2 is a waste product • O2 is used in cellular respiration

  39. Pulmonary respiration • Internal respiration

  40. Gas transport in blood • Carbon dioxide • 70% as bicarbonate ion (HCO3-) dissolved in plasma • 23% bound to hemoglobin • 7% as CO2 dissolved in plasma • Oxygen • 99% bound to hemoglobin • 1% as O2 dissolved in plasma

  41. Control of breathing • Respiratory centre in reticular formation of the brain stem • Medullary rhythmicity centre • Controls basic rhythm of respiration • Inspiratory (predominantly active) and expiratory (usually inactive in quiet respiration) neurones • Drives muscles of respiration • Pneumotaxic area • Inhibits inspiratory area • Apneustic area • Stimulates inspiratory area, prolonging inspiration

  42. Regulation of respiratory centre • Chemical regulation • Most important • Central and peripheral chemoreceptors • Most important factor is CO2 (and pH) •  in arterial CO2 causes  in acidity of cerebrospinal fluid (CSF) •  in CSF acidity is detected by pH sensors in medulla • medulla  rate and depth of breathing