Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Responding to ill Health Life Science The Respiratory System Anatomography (2012) https://commons.wikimedia.org/wiki/File:Internal_intercostal_muscles_frontal2.png 1 Learning Outcomes • Discuss the structure and function of the respiratory • • • • system. Explain the principles of gas exchange and diffusion of O2 and CO2. Explain the principles involved in the process of respiration and the common lung volumes. Describe factors affecting the efficiency of ventilation (i.e. compliance, airway resistance and surfactant). Explain the significance of pCO2 and pO2 as a stimulus for breathing and the underlying principles behind chemical nervous control of this process. 2 Ventilation - movement of air in and out of lungs Respiration - exchange of gases external respiration exchange of gases by diffusion between alveoli in lungs and blood in pulmonary capillaries internal respiration exchange of gases by diffusion between blood in systemic capillaries and body cells 3 The Respiratory System Main function ?? transfer of: oxygen (air blood) carbon dioxide (blood air) Other functions ?? some metabolism filtration of toxins from blood blood reservoir 4 Structure & Function Divided into: Upper tract nose mouth pharynx head / neck Lower tract • • • • larynx trachea bronchi lungs neck / chest 5 Function of Upper Respiratory Tract Nasal Pharyngeal cavities Laryngeal All : filter, heat & moisten air – have rich blood supply – produce copious mucus Epiglottis: – at entrance to trachea (& oesophagus) – small flap of cartilage – blocks trachea during swallowing BruceBlaus (2013) https://commons.wikimedia.org/wiki/File:Blausen_0872_UpperRespiratorySystem.png 6 Structure of Lung and Pleura each lung divided into lobes lobes divided into segments segments subdivided into lobules CRUK (2014) https://commons.wikimedia.org/wiki/File:Diagram_showing_the_removal_of_one_lobe_of_the_lung_(lobectomy)_CRUK_366.svg 7 Structure of Lung and Pleura each lung covered by thin epithelial layer i.e. pleura – has 2 layers: visceral pleura outer surface of lung parietal pleura inner chest wall pleural space contains watery pleural fluid = lubricant • pleura / lung pericardium / heart • allows virtually frictionless movement OpenStax College (2013) 2313 The Lung Pleurea https://commons.wikimedia.org/wiki/File:2313_The_Lung_Pleurea.jpg 8 AIRWAYS & AIR FLOWS air conducted in/out of lungs via branching respiratory tree held open by C-shaped rings of cartilage lined by ciliated epithelium sweeps carpet of mucus (traps particles) out of lung •BruceBlaus (2013 •https://commons.wikimedia.org/wiki/File:Blausen_0865_TracheaAnatomy.png 9 BruceBlaus (2013) https://commons.wikimedia.org/wiki/File:Blausen_0766_RespiratoryEpithelium.png 10 Lower respiratory tract trachea divides progressively into: main bronchi secondary bronchi tertiary bronchi terminal bronchioles (smallest airways without alveoli) all have no part in gas exchange anatomical dead space total volume approx 150ml of air 11 Lower Respiratory Tract terminal bronchioles divide sequentially into: respiratory bronchioles (a few alveoli) alveolar ducts (completely lined with alveoli) gas exchange occurs here (respiratory zone) volume 2.5 to 3 litres in each lung NB. as airways get narrower, become more numerous 12 Cycle of respiration 12 to 15 times / minute: inspiration expiration pause 13 VENTILATION air moves from high pressure to low pressure Inspiration (lung air intake) volume of chest intrathoracic pressure air sucked into lungs • achieved by: – diaphragm contracting (pulling down) – external intercostal muscles (pull ribs up & out) 14 INSPIRATION air sucked in to the level of terminal bronchioles terminal bronchiole alveoli air transport via DIFFUSION: • large Cross Sectional Area • slow airspeed - can lead to dust settling in terminal bronchioles LadyofHats (2008) http://commons.wikimedia.org/wiki/File:Inhalation_diagram.svg 15 Expiration • elastic lungs recoil when inspiratory muscles rest (i.e. passive) intrathoracic air ‘forced’ out pressure lungs LadyofHats (2008) https://commons.wikimedia.org/wiki/File:Expiration_diagram.svg 16 Expiration (cont.d) during EXERCISE: • expiration becomes ‘active’ • abdominal muscles contract, forcing diaphragm upward • internal intercostal muscles contract, pulling ribs down and inward thoracic these actions: volume thoracic pressure assists expiration 17 Factors Affecting Ventilation Compliance measure of ‘stretchability’ effort required to inflate lungs lungs normally very compliant Airway Resistance (resistance to airflow) normally very low thus pressure needed to move air is small ( work) 18 Factors Affecting Ventilation Compliance Airway Resistance (resistance to airflow) Surface Tension surface of alveoli moist to promote gas exchange this moisture leads to surface tension, tending to collapse alveoli problem averted by surfactant: secreted by alveolar cells acts like detergent surface tension dramatically 19 Factors Affecting Ventilation Normally - high compliance lungs have - low airway R low energy cost to breathing However, if • compliance (scarring) • resistance (inflammation) • surfactant ‘work’ of breathing also, alveoli collapse e.g. respiratory distress syndrome 20 Lung volumes total capacity approx 6 litres tidal volume volume moved in & out at each inspiration/expiration (0.5 L at rest) inspiratory & expiratory reserve volumes volumes of air that can be inspired & expired, over & above tidal volume 21 Lung volumes vital capacity maximal volume that can be exhaled (typically approx 4.8L) ( inspiratory reserve volume + tidal volume + expiratory reserve volume) residual volume (typically approx 1.2L) gas remaining in lungs after maximal expiration in anatomical dead space & in alveoli to keep them open 22 M•Komorniczak (2009) https://commons.wikimedia.org/wiki/File:Lung_Volumes_And_Capacities_en.svg 23 Lung Volumes . Minute Volume (V) total volume of air breathed in/out each minute . V = tidal volume x respiratory rate (L/min) (L/breath) (breaths/min) 24 Lung Volumes . Minute Volume (V ) At rest: tidal volume 0.5L, 12 breaths/min minute volume = 0.5 x 12 = 6L /min taking into account dead space (150mL) (500 – 150) x 12 = 4.2 L/min fresh air available for gas exchange (known as alveolar ventilation) If body’s demand for oxygen increases, tidal & minute volumes increase markedly 25 Blood-Air Interface Concentration of a gas is related to its pressure (P) oxygen & carbon dioxide move between air and blood by diffusing down their pressure gradients diffusion rate increases with: surface area pressure gradient thickness of surface blood-air barrier in lung ideal for gas exchange: very thin very large surface area (50-100 m2) LadyOfHats (2007) Alveolus diagram https://commons.wikimedia.org/wiki/File:Alveolus_diagram.svg 26 Partial Pressures concentration of gas in mixture referred to as partial pressure (P) The atmosphere consist of approximately: 20 % oxygen 0.05 % carbon dioxide 80 % nitrogen Air pressure is ~760 mmHg therefore: pO2 + pCO2 + pN2 = 760mmHg pO2 = 20% of 760 = 160 mmHg pCO2 = 0.05% of 760 = 0.4 mmHg 27 alveolus Which way will oxygen flow ?? capillary pO2 100 mmHg pO2 40 mmHg 0.3 m Impairment of Diffusion e.g. high altitude - press. gradient between air & blood e.g. fibrosis - thickening of exchange barrier e.g. emphysema - lung surface area UWS Staff (2015) 28 Gas Exchange pressure of CO2 in : blood entering pulmonary capillary 44mmHg alveolar air 40mmHg Which way does carbon dioxide flow? alveolus capillary pCO2 40 mmHg pCO2 44 mmHg 0.3 m UWS Staff (2015) 29 Control Mechanisms & Regulation breathing usually automatic can be consciously controlled negative feedback - basic principle of control of breathing (whether conscious or not) 30 Control mechanisms negative feedback sensors gather information control unit (in brain) analyses information & initiates response effectors produce required change 31 Respiratory Control sensors: many different sensors involved in control of normal respiration most important - chemoreceptors 32 Levels of pO2 and pCO2 determine manner in which we breathe Medullary Respiratory Centre sympathetic + parasymp. NS Respiratory muscles Sensor blood gases chemoreceptors UWS Staff (2015) 33 Sensors in Automatic Respiratory Control chemoreceptors respond to changed blood levels of: O2 CO2 H + normal partial pressures in arterial blood are O2 100mmHg CO2 40mmHg 34 Sensors in Automatic Respiratory Control chemoreceptors : in brain: • sense changes in pCO2 & H + concentration in CSF surrounding brain in some major arteries: • sense changes in arterial pO2, pCO2 & H + concentration increased pCO2 & H + or decreased pO2 bring about increased respiratory effort (& vice versa) 35 Respiratory Control other sensors include stretch receptors in the lung these modify respiration to degree of lung stretch: stretch respiratory rate ( expiration time) stretch respiratory rate (stimulates inspiratory muscles) lung has receptors in airways, nose, trachea etc. – stimulation reflex constriction (e.g. asthma) all control mechanisms involve ANS voluntary control initiated in cerebral cortex can over-ride automatic control – but only briefly 36 SUMMARY Respiratory system comprises upper & lower parts Lungs: have a branching respiratory tree are surrounded by the pleura Ventilation is affected by: compliance resistance surface tension Blood-air interface gas exchange via diffusion 37