Respiratory System PDF

L26- RESPIRATORY SYSTEM Dr.Pugazhandhi Bakthavatchalam Assistant Professor of Anatomy and Physiology, AUACAS, American University of Antigua LEARNING OUTCOMES Pleura and Diaphragmatic recess Define Lung (pulmonary) compliance and its determinants Describe the role...

L26- RESPIRATORY SYSTEM Dr.Pugazhandhi Bakthavatchalam Assistant Professor of Anatomy and Physiology, AUACAS, American University of Antigua LEARNING OUTCOMES Pleura and Diaphragmatic recess Define Lung (pulmonary) compliance and its determinants Describe the role of elastic fibers of lung parenchyma in compliance Describe the role of pulmonary surfactant on surface tension and its clinical significance  PLEURA  It is a closed serous sac.  PLEURA – LAYERS: - 2 layers – Parietal & Visceral - Both layers are continuous around lung roots & pulmonary ligaments  VISCERAL / PULMONARY PLEURA: - Closely invests lung (except at hilum & at the attachment of lung root) & inseparable from it  PARIETAL PLEURA: -Named according to the structures it lines - Subdivided into Costal, Diaphragmatic, Cervical & Mediastinal pleurae COSTAL PLEURA  Lines inner surface of sternum, ribs & costal cartilages, intercostal spaces & sides of vertebral bodies DIAPHRAGMATIC PLEURA  Covers thoracic surface of corresponding part of diaphragm  CERVICAL PLEURA  From inner border of 1st rib to cover the apex of lung, passes downward & medially to continue with mediastinal pleura  MEDIASTINAL PLEURA  Forms lateral boundary of mediastinum and covers the mediastinal surface of the lungs  RECESSES OF PLEURA Widening of pleural cavity Folds of parietal pleura which act as reserve spaces for lungs to expand during deep inspiration  COSTO-MEDIASTINAL RECESS Between costal & mediastinal pleurae Prominent in relation to cardiac notch of lung  COSTO-DIAPHRAGMATIC RECESS Potential space between lower limit of pleural sac & lower border of corresponding lung  COSTO-DIAPHRAGMATIC RECESS At mid-clavicular, mid-axillary & scapular lines respectively, Lower limit of pleura – 8th, 10th & 12th ribs Lower border of lung – 6th, 8th, 10th ribs  COSTO-DIAPHRAGMATIC RECESS Functions Allows expansion of lungs in full inspiration Most dependent part of pleural sac If fluid appears in pleural sac, fluid collects first in Costo-diaphragmatic recess DETERMINANTS OF LUNG COMPLIANCE Both lungs and thoracic cage are 3. viscoelastic structures and therefore can be expanded (stretched) The measure of expansibility/ distensibility is known as compliance 1. The elastic property of lung is due to tissue elastic forces contributed by elastin and collagen fibres of lung parenchyma elastic forces caused by surface tension of the fluid lining alveoli 2. The elastic property of thoracic cage is due to the elastic nature of ribs, muscle & tendon 9-Oct-24 14  Lung Compliance Extent to which the lungs expand for each unit increase in transpulmonary pressure Total compliance of both lungs together in normal adult: 200 ml of air per cm of water transpulmonary pressure Contd… Tissue elastic forces = represent 1/3 of total lung elasticity Fluid air surface tension elastic forces in alveoli = 2/3 of total lung elasticity. Contd… Two Curves: Inspiratory compliance curve Expiratory compliance curve The total work of breathing of the cycle is the area contained in the loop.  DEFINITION & VALUES OF COMPLIANCE Compliance of the Lungs & chest wall = V/P The change of lung volume per unit change in airway/ alveolar pressure – 0.13L/cm of H2O So (stretchability / expandability / compliance) of the lungs and chest wall – 0.13L/cm of H2O Compliance of the Lungs alone The change of lung volume (without thoracic cage) per unit change in airway / alveolar pressure – 0.2 L/cm of H2O Compliance = ΔV/of The compliance Δ Plungs is greater than lungs and thoracic cage combined.  Changes in lung volume, alveolar pressure, pleural pressure, and transpulmonary pressure during normal breathing Contraction and expansion of the thoracic cage during expiration and inspiration PULMONARY COMPLIANCE PRESSURE – VOLUME CURVE Compliance is a static Hysteresis loop measure of lung and chest recoil Expiratory Compliance is the slope of the compliance pressure-volume The curve curve is not the same during curve inflation and deflation - This is termed hysteresis Inspiratory Lung volume at any given pressure compliance curve during inhalation is less than the lung volume at any given pressure during exhalation. Calculations Normal compliance = 0.1 Liter/cmH2O Volume = 0.5 liters = 0.1 L/cmH2O Pressure 5 cmH2O Low compliance = 0.05 Liter/cmH2O Volume = 0.5 liters = 0.05 L/cmH2O Pressure 10 cmH2O Stiffer lung needs more inflation pressure High compliance = 0.17 Liter/cmH2O Volume = 0.5 liters = 0. 17 L/cmH2O Pressure 3 cmH2O Floppier lung needs less inflation pressure  The slope of the loop will be Steeper when compliance increases Pressure-Volume Flatter when compliance decreases loop High Compliance V The compliance curve is o shifted downwards and to the right (decreased l Normal Compliance compliance) in interstitial pulmonary fibrosis and pulmonary congestion Low compliance Compliance curve shifts upward and to the left (increased compliance) in Pressure emphysema FACTORS AFFECTING COMPLIANCE Compliance is decreased (curve is shifted downward and to the right) in: pulmonary congestion interstitial pulmonary fibrosis Supine position Restrictive lung disease Pneumothorax Hydrothorax Asthma Compliance is increased in (curve is shifted upward and to the left) in: Emphysema / Old age 9-Oct-24 23 3. SURFACE TENSION The alveoli are lined by a thin layer of fluid In each alveolus there is an interface between air and water The water molecules at the superficial layer (boundary) of alveolar fluid are attracted laterally & inwardly This makes the fluid layer to shrink or minimize liquid-air interface (surface tension) and the alveolus tends to collapse Surfactant resists the collapse of lung 9-Oct-24 24 ACTION OF SURFACTANT Presence of surfactant reduces the surface tension Surfactant content of each alveolus is relatively constant So when the alveolus size decreases  alveolar surfactant conc. increases  lowers surface tension. 9-Oct-24 25 FUNCTIONS OF ALVEOLAR SURFACTANT Alveolar Stabilization Surfactant enables alveoli of different radius to remain at equilibrium Prevention of collapse of alveoli Alveoli become smaller during expiration Prevent pulmonary edema Surfactant deficient cause high surface tension of alveoli This draws fluids from capillaries leading to pulmonary edema Increases lung compliance Reduces the centripetal force of surface tension in alveoli And increases stretch ability of lungs Immune function Regulates lung inflammation, Facilitates phagocytosis 9-Oct-24 26 SURFACTANT It is a lipid surface-tension-lowering agent. If the surface tension is not kept low when the alveoli become smaller during expiration, they collapse. It is a mixture of dipalmitoylphosphatidylcholine (DPPC), other lipids, and proteins Law of Laplace: P = 2 T/r distending pressure equals two times the tension divided by the radius If alveoli have half the normal radius the pressures are doubled Use of Surfactant: It prevents collapse during expiration It prevent pulmonary oedema  Laplace’s Law: Relates pressure to (surface) tension and radius Pressure = 2T/r  small radius = High Pressure Without surfactant small alveoli would empty into bigger alveoli and collapse  In presence of surfactant, surface tension is no longer a constant! Surface tension in small alveoli lower than in large alveoli Small and large alveoli can co-exist COMPONENTS OF SURFACTANTS 9-Oct-24 31  FORMATION OF SURFACTANT Components of surfactant are synthesized from precursors in the endoplasmic reticulum and transported through Golgi apparatus by multi-vesicular bodies. Components are packaged in lamellar bodies, intracellular storage granules Secretion (exocytosis) into the liquid lining of the alveolus, surfactant phospholipids are organized into a complex lattice called tubular myelin Tubular myelin is believed to generate the phospholipid that provides material for a monolayer at the air-liquid interface in the alveolus, lowers surface tension  METABOLISM OF SURFACTANT Surfactant phospholipids and proteins are subsequently taken back into type II cells, in the form of small vesicles and transported for storage into lamellar bodies for recycling Alveolar macrophages also take up some surfactant in the liquid layer. phospholipid components of surfactant remain in the alveolar lumen for few hours and taken back into type II cell and is reused 10 times before being degraded.  IRDS Respiratory distress syndrome of the newborn/infant respiratory distress syndrome (IRDS)/ hyaline membrane disease surfactant does not normally secreted into the alveoli until 6- 7 months (or even later) of gestation. Many premature babies have little or no surfactant and their lungs have an extreme tendency to collapse Pressure-Volume curve in HMD Improvements in morbidity and mortality in infants with IRDS by: 1. use of antenatal steroids to enhance pulmonary maturity 2. Appropriate resuscitation – immediate use of continuous positive airway pressure (CPAP) 1. Early administration of surfactant (Survanta) 9-Oct-24 34 SUMMARY 9-Oct-24 35 Supported by ELASTIC FIBERS 36  REFERENCES Drake R.L., Gray’s Anatomy for Students, 2nd Edition, 2009, Churchill Livingstone Moore, Clinically Oriented Anatomy, 6th Edition, 2009, Lippincott Williams & Wilkins Textbook of Medical Physiology – Guyton & Hall Medical Physiology – R.K Marya 9-Oct-24 37