Chapter 32 Structure and Function of the Pulmonary
- Slides: 50
Chapter 32 Structure and Function of the Pulmonary System Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 1
Structures of the Pulmonary System Airways Blood vessels Chest wall Lungs Lobes Ø Segments Ø Lobules Ø Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 2
Structures of the Pulmonary System Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 3
Structures of the Pulmonary System Conducting airways Upper airways • Nasopharynx • Oropharynx Ø Larynx • Connects upper and lower airways Ø Lower airways • Trachea • Bronchi • Terminal bronchioles Ø Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 4
Structures of the Pulmonary System Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 5
Structures of the Pulmonary System Gas-exchange airways Respiratory bronchioles Ø Alveolar ducts Ø Alveoli • Epithelial cells Ø Type I alveolar cells – Alveolar structure Type II alveolar cells – Surfactant production Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 6
Structures of the Pulmonary System Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 7
Structures of the Pulmonary System Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 8
Structures of the Pulmonary System Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 9
Gas Exchange Alveoli Primary gas-exchange units Ø Pores of Kohn • Permit air to pass through the septa from alveolus to alveolus Ø Collateral ventilation and even air distribution Lungs contain approximately 25 million alveoli at birth and 300 million by adulthood Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 10
Pulmonary and Bronchial Circulation Pulmonary circulation has a lower pressure than systemic circulation (18 mm. Hg) Only one third of vessels filled with blood at any given time Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 11
Pulmonary and Bronchial Circulation Pulmonary artery divides and enters the lung at the hilus Each bronchus and bronchiole has an accompanying artery or arteriole Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 12
Pulmonary and Bronchial Circulation Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 13
Pulmonary and Bronchial Circulation Alveolocapillary membrane Formed by shared alveolar and capillary walls Ø Thin membrane of alveolar epithelium, the alveolar basement membrane, interstitial space, the capillary basement membrane, and the capillary endothelium Ø Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 14
Pulmonary and Bronchial Circulation Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 15
Chest Wall and Pleura Chest wall Skin, ribs, and intercostal muscles Ø Thoracic cavity Ø Pleura Serous membrane Ø Parietal and visceral layers Ø Pleural space (cavity) Ø Pleural fluid Ø Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 16
Lung Functions Gas exchange Supply oxygen Ø Eliminate CO 2 Ø Maintain p. H Eliminate water Other functions Maintain normal body temperature Ø Immune responses Ø Hormone secretion Ø Metabolism Ø Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 17
Requirements for Ventilation, Perfusion, and Diffusion Adequate inspired O 2 – (Fi. O 2) Ventilation and perfusion of alveoli A permeable alveolocapillary membrane Adequate blood flow Ability to transport O 2 and CO 2 Ability of cell to use O 2 and eliminate CO 2 Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 18
Requirements for Ventilation, Perfusion, and Diffusion Adequate inspired O 2 – (Fi. O 2) Barometric pressure is 760 at sea level 21% x 760 = partial pressure of O 2 at sea level = ~160 mm. Hg Barometric pressure is 600 at Salt Lake City (much lower on Mt. Everest) 21% x 600 = partial pressure of O 2 at SLC = ~126 mm. Hg Why we give oxygen at high altitude Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 19
Function of the Pulmonary System Ventilation Mechanical movement of gas or air into and out of the lungs Ø Minute volume • Ventilatory rate multiplied by the volume of air per breath Ø Alveolar ventilation Ø Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 20
Lung Volumes and Capacities Based on Age, Gender, Height Dead space: oropharynx to division 16 (about equal to ideal body weight) Tidal volume (per breath) 400 -800 ml IRV 3000 ml additional air that could be inhaled Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 21
Lung Volumes and Capacities Based on Age, Gender, Height ERV 1000 ml remaining air Can be forcefully expired after normal expiration FEV 1 Ø Why abdominal thrusts work; expel TV plus ERV Ø Forced vital capacity (theoretical) Ø TV + IRV + ERV ~4500 -5000 ml Residual volume constant ~1200 ml Ø Air remaining in alveoli Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 22
Formulas Minute ventilation (or volume/min) RR x TV Ø RR 16, TV 500 Ø 16 x 500 = 8000 ml/min Ø Effective minute volume: RR x (TV-DS) 100 lb, RR 16, TV 500 ml Ø 16 (500 -100) = 6400 ml/min Ø Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 23
Control of Ventilation ANS Ø Stimulates smooth muscle (contract relax) • Airway lumen diameter Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 24
Terms Hypoxia Ø Low oxygen in the cell Hypoxemia Ø Low oxygen in arterial blood (low O 2 saturation) Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 25
Control of Ventilation Chemoreceptors Central receptors • Reflects Pa. CO 2 • Stimulated by H+ in cerebrospinal fluid (p. H) Ø Peripheral receptors • Aorta and carotid bodies • Stimulated by hypoxemia (Pa. O 2) Ø Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 26
Control of Ventilation Irritant receptors: epithelium of conducting airways Ø Cough, bronchoconstriction, decrease RR Stretch receptors: protective Ø Decrease RR and volume Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 27
Ventilation Neurochemical control Respiratory center • Dorsal respiratory group • Ventral respiratory group • Pneumotaxic center • Apneustic center Ø Peripheral chemoreceptors Ø Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 28
Ventilation Neurochemical control Lung receptors • Irritant receptors • Stretch receptors • J-receptors Ø Chemoreceptors • Central chemoreceptors • Peripheral chemoreceptors Ø Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 29
Mechanics of Breathing Major and accessory muscles Major muscles of inspiration • Diaphragm • External intercostals Ø Accessory muscles of inspiration • Sternocleidomastoid and scalene muscles Ø Accessory muscles of expiration • Abdominal and internal intercostal muscles Ø Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 30
Muscles of Ventilation Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 31
Overview: Mechanics of Breathing Alveolar surface tension Ø Function of surfactant Elastic properties of lung and chest wall Elastic recoil Ø Compliance Ø Airway resistance Airway size Ø Gas velocity (Poiseuille’s law) Ø Muscular effort Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 32
Mechanics of Breathing Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 33
Surface Tension of Water Tendency of water molecules to contract to the smallest possible surface area (bead) with exposure to air Increased surface tension = increased work of breathing Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 34
Laplace’s Law The smaller a sphere’s radius (alveoli) the greater the surface tension and the more difficult (work) to expand the alveoli P = 2 t/r P = pressure inside a sphere (alveoli) Ø t = surface tension Ø r = radius of a sphere Ø Surfactant reduces fluid surface tension lining the alveoli and decreases tendency to collapse, preventing atelectasis Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 35
Compliance A measure of lung and chest wall distensibility or “stiffness” ― volume of air moved ― force to move the air Low: increased work of inspiration Ø Stiff lungs High: increased work of expiration Ø Baggy lungs Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 36
Measurement of Gas Pressure Barometric pressure Ø Partial pressure of water vapor Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 37
Measurement of Gas Pressure Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 38
Measurement of Gas Pressure Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 39
Gas Transport Four steps Ventilation of the lungs Ø Diffusion of oxygen from the alveoli into the capillary blood Ø Perfusion of systemic capillaries with oxygenated blood Ø Diffusion of oxygen from systemic capillaries into the cells Ø Diffusion of CO 2 occurs in reverse order Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 40
Gas Transport Distribution of ventilation and perfusion Gravity and alveolar pressure Ø Ventilation-perfusion ratio Ø Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 41
Gas Transport: O 2 Oxygen transport Diffusion across alveolocapillary membrane Ø Determinants of arterial oxygenation Ø Oxyhemoglobin association and dissociation • Oxyhemoglobin dissociation curve Ø Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 42
Gas Transport: CO 2 Carbon dioxide transport Dissolved in plasma Ø Bicarbonate Ø Carbamino compounds Ø Haldane effect Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 43
Measurement of Gas Pressure Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 44
Measurement of Gas Pressure Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 45
Clinical Manifestations: Hypoxemia Early Tachycardia Ø Mild increase in blood pressure Ø Diaphoresis (stress response) Ø Confusion (CNS response) Ø Loss of judgment Ø Cyanosis after 5 g desaturation Ø Late Stupor Ø Decreased BP, myocardium not getting enough O 2 Ø Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 46
Control of Pulmonary Circulation Hypoxic vasoconstriction Caused by low alveolar PO 2 Ø Blood is shunted to other, well-ventilated portions of the lungs • Better ventilation and perfusion matching • If hypoxia affects all segments of lungs, the Ø vasoconstriction can result in pulmonary hypertension Acidemia also causes pulmonary artery constriction Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 47
Tests of Pulmonary Function Spirometry Diffusion capacity Residual volume Functional reserve capacity (FRC) Total lung capacity Arterial blood gas analysis Chest radiographs Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 48
Aging and the Pulmonary System Loss of elastic recoil Stiffening of the chest wall Alterations in gas exchange Increases in flow resistance Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 49
Aging and the Pulmonary System Mosby items and derived items © 2010, 2006 by Mosby, Inc. , an affiliate of Elsevier Inc. 50
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