The Respiratory System B.pptx

Week 2 Lecture 6b The Respiratory System Lecturer: Audrey I. Stephen The Respiratory System This topic relates to: Learning outcome(s) Explain the mechanics of ventilation Identify key respiratory volumes Introduce control of the respiratory system Formative and summative assessment Any topic within...

Week 2 Lecture 6b The Respiratory System Lecturer: Audrey I. Stephen The Respiratory System This topic relates to: Learning outcome(s) Explain the mechanics of ventilation Identify key respiratory volumes Introduce control of the respiratory system Formative and summative assessment Any topic within this module could potentially have a question(s) in the exam paper Links with other topics in the module Links with cardiovascular system, nervous system, homeostasis, muscular system Links with other modules and stages Stages 2 and 3 sciences Links to nursing and paramedic practice Essential knowledge for caring for people with respiratory disease, carrying out CPR, providing airway support. 2 Respiratory Tract: Pleural Membranes A serous membrane called the pleura surrounds the lungs Forms a pleural cavity around each lung Parietal pleura – lining thoracic cavity, diaphragm and mediastinum Continuous with Visceral pleura lining lungs Pleural cavity contains pleural fluid Lubricant Holds pleural membranes together 3 Mechanics of breathing (ventilation) Ventilation (breathing): movement of air from outside the body into the bronchial tree and alveoli, and back out Composed of inspiration (inhalation) and expiration (exhalation) Inspiration: Air moves from higher to lower pressure Atmospheric pressure: pressure exerted by the air on all objects in contact with it; force that moves air into the lungs When pressure inside the lungs decreases below atmospheric pressure, air flows in from the atmosphere; this occurs during inspiration Increasing the volume of the thoracic cavity causes air pressure inside the lungs to decrease 4 Inspiration Maximal inspiration (a deep breath): requires contraction of several muscles other than the diaphragm (pectoralis minor, sternocleidomastoid, scalenes), to enlarge the thoracic cavity even more Due to surface tension between the two layers of the pleura, as the thoracic cavity expands, the lungs expand with it Surface tension, however, is not advantageous in the alveoli; it would tend to cause alveolar collapse As the lungs expand in size, a lipoprotein mixture called surfactant keeps the alveoli inflated, preventing collapse 5 Muscles of Inspiration 6 Muscles of Expiration 7 Expiration Atmospheric air pressure equals alveolar air pressure External intercostal muscles relax – ribs move down and in Diaphragm relaxes – flattened dome shape Lung volume decrease alveolar air pressure increases Alveolar air pressure greater than atmospheric pressure Air moves out of the lungs A passive process in quiet breathing 8 Mechanisms of Breathing: Normal Inspiration and Expiration Respiratory volume and capacities Spirometry: study of various air volumes that move into and out of the lungs due to different degrees of effort One inspiration followed by expiration is called a respiratory cycle There are 4 distinct respiratory volumes: Tidal volume (TV): volume of air entering or leaving the lungs during one respiratory cycle; average is ~500 mL Inspiratory reserve volume (IRV): volume of air that can be inhaled in addition to the tidal volume, during forced inspiration; average is ~3,000 mL Expiratory reserve volume (ERV): volume of air that can be exhaled during a maximal forced expiration, beyond the tidal volume; average is ~1,200 mL Residual volume (RV): volume of air that remains in the lungs after a maximal expiration; average is ~1,200 mL; cannot be measured with a spirometer Lung Volumes 11 Table. Respiratory volumes and capacities Control of breathing 13 Factors Affecting Breathing Chemicals, lung tissue stretching, emotional state, and level of physical activity affect breathing Central chemoreceptors are chemosensitive areas associated with the respiratory centers in medulla oblongata: Sensitive to changes in the concentration of CO2 and H+ ions in the cerebrospinal fluid, which represents blood concentrations If either CO2 or H+ ion concentrations rise (pH decreases), the central chemoreceptors signal the respiratory center, and breathing rate and depth increase As more CO2 is exhaled, blood and CSF levels fall, and breathing returns to normal Summary This lecture has covered: Functions of the respiratory system as a whole and the individual parts of the system in more detail The mechanisms of breathing for inspiration and expiration Respiratory volumes and capacities The control of breathing Lecture c will focus on: The development of the respiratory system in the embryo The aging respiratory system