Physiology of Respiration PDF

Malaysian Allied Health Sciences Academy Faculty of Pharmacy and Biomedical Sciences Bachelor of Pharmacy ANA 6123 Anatomy and Physiology II Physiology of Respiration Chong Ho Phin (Ph.D.) [email protected]...

Malaysian Allied Health Sciences Academy Faculty of Pharmacy and Biomedical Sciences Bachelor of Pharmacy ANA 6123 Anatomy and Physiology II Physiology of Respiration Chong Ho Phin (Ph.D.) [email protected] 1  Subtopics and learning outcomes Subtopics: 1. Physiology of the respiratory system Learning outcomes: Students should be able to: List the functions of the respiratory system Describe gas and pressure changes during pulmonary ventilation State the mechanism of respiration Name the muscles involved in respiration and accessory muscles of inspiration Describe intrapleural and intraplumonic pressure Describe the factors affecting pulmonary ventilation 2 Explain lung volumes and capacities  Function of the respiratory system Provides oxygen Eliminates carbon dioxide Regulates blood pH Forms speech sounds (phonation) Defends against microbes 3  Gas exchange The process of gas exchange in the body, called respiration, has three basic steps: 1. Pulmonary ventilation or breathing, is the inhalation and exhalation of air 2. External (pulmonary) respiration is the exchange of gases between the alveoli of the lungs and the blood in pulmonary capillaries 3. Internal (tissue) respiration is the exchange of gases between blood in systemic capillaries and tissue cells 4  Pressure changes during pulmonary ventilation Air always flows from a region of higher pressure to a region of lower pressure Air moves into the lungs when the air pressure inside the lungs is less than the air pressure in the atmosphere Air moves out of the lungs when the air pressure inside the lungs is greater than the air pressure in the atmosphere 5  Mechanism of respiration Inhalation Internal intercoastal muscle relaxed External intercoastal muscle contract Rib cage move upwards & outwards Diaphragm contracts and flattens Volume of thorax cavity increase Pressure in alveoli decrease 6  Mechanism of respiration Exhalation Internal intercoastal muscle contract External intercoastal muscle relaxed Rib cage moves downwards and upwards Diaphragm relaxes Volume of thorax cavity decrease Pressure in alveoli increase 7 Mechanism of respiration 8  Muscles of respiration The expansion of the chest during inspiration occurs as a result of muscular activity, partly voluntary and partly involuntary The main muscles of respiration in normal quiet breathing are the intercostal muscles and the diaphragm During difficult or deep breathing they are assisted by the muscles of the neck, shoulders and abdomen 9  Muscles of respiration – Diaphragm The most important muscle of inhalation is the diaphragm, the dome-shaped skeletal muscle that forms the floor of the thoracic cavity It is innervated by fibers of the phrenic nerves, which emerge from the spinal cord. Contraction of the diaphragm causes it to flatten, lowering its dome. This increases the vertical diameter of the thoracic cavity 10  Muscles of respiration – Diaphragm During normal quiet inhalation, the diaphragm descends about 1 cm, producing a pressure difference of 1–3 mmHg and the inhalation of about 500 mL of air During strenuous breathing, the diaphragm may descend 10 cm, which produces a pressure difference of 100 mmHg and the inhalation of 2–3 liters of air 11  Muscles of respiration – External intercostal muscle The next most important muscles of inhalation are the external intercostal muscle When these muscles contract, they elevate the ribs As a result, there is an increase in the anteroposterior and lateral diameters of the chest cavity 12  Accessory muscles of inspiration Involved in forced inspiration E.g. exercise, coughing, sneezing, asthma Scalene: contraction enlarges the upper rib cage Major/minor pectoralis: draws rib cage superiorly Sternocleidomastoid: elevates sternum 13  Inhalation During quiet inhalations, the pressure between the two pleural layers in the pleural cavity, called intrapleural (intrathoracic) pressure, is always subatmospheric (lower than atmospheric pressure) Just before inhalation, it is about 4 mmHg less than the atmospheric pressure, or about 756 mmHg at an atmospheric pressure of 760 mmHg 14  Intrapleural pressure As the diaphragm and external intercostals contract and the overall size of the thoracic cavity increases, the volume of the pleural cavity also increases, which causes intrapleural pressure to decrease to about 754 mmHg. During expansion of the thorax, the parietal and visceral pleurae adhere tightly because of the subatmospheric pressure between them and because of the surface tension created by their moist adjoining surfaces As the thoracic cavity expands, the parietal pleura lining the cavity is pulled outward in all directions, and the visceral pleura and lungs are pulled along with it 15 Intrapleural pressure 16  Alveolar (intrapulmonic) pressure As the volume of the lungs increases in this way, the pressure inside the lungs, called the alveolar (intrapulmonic) pressure, drops from 760 to 758 mmHg A pressure difference is thus established between the atmosphere and the alveoli Because air always flows from a region of higher pressure to a region of lower pressure, inhalation takes place 17  Active and passive processes of inhalation Because both normal quiet inhalation and inhalation during exercise or forced ventilation involve muscular contraction, the process of inhalation is said to be active process Normal exhalation during quiet breathing, unlike inhalation, is a passive process because no muscular contractions are involved 18  Exhalation Breathing out, called exhalation (expiration) The pressure in the lungs is greater than the pressure of the atmosphere Exhalation results from elastic recoil of the chest wall and lungs, both of which have a natural tendency to spring back after they have been stretched Two inwardly directed forces contribute to elastic recoil: (1) The recoil of elastic fibers that were stretched during inhalation (2) The inward pull of surface tension due to the film of alveolar fluid 19  Exhalation Exhalation starts when the inspiratory muscles relax As the diaphragm relaxes, its dome moves superiorly owing to its elasticity As the external intercostals relax, the ribs are depressed These movements decrease the vertical, lateral, and anteroposterior diameters of the thoracic cavity, which decreases lung volume 20  Other Factors Affecting Pulmonary Ventilation Three other factors affect the rate of airflow and the ease of pulmonary ventilation: 1. Surface tension of the alveolar fluid 2. Compliance of the lungs 3. Airway resistance 21  Other Factors Affecting Pulmonary Ventilation Surface tension of the alveolar fluid A thin layer of alveolar fluid coats the luminal surface of alveoli and exerts a force known as surface tension Surface tension arises at all air–water interfaces because the polar water molecules are more strongly attracted to each other When liquid surrounds a sphere of air, as in an alveolus or a soap bubble, surface tension produces an inwardly directed force 22  Other Factors Affecting Pulmonary Ventilation Surface tension of the alveolar fluid During breathing, surface tension must be overcome to expand the lungs during each inhalation Surface tension also accounts for two-thirds of lung elastic recoil, which decreases the size of alveoli during exhalation 23  Other Factors Affecting Pulmonary Ventilation Compliance of the lungs Compliance refers to how much effort is required to stretch the lungs and chest wall High compliance means that the lungs and chest wall expand easily; low compliance means that they resist expansion In the lungs, compliance is related to two principal factors: elasticity and surface tension Healthy lungs have high compliance and expand easily because elastic fibers in lung tissue are easily stretched and surfactant in alveolar fluid reduces surface tension Decreased compliance includes presence of scar lung tissue, lung tissue filled with fluid, deficiency in surfactant and impedance of lung expension 24  Other Factors Affecting Pulmonary Ventilation Airway resistance The rate of airflow through the airways depends on both the pressure difference and the resistance: Airflow equals the pressure difference between the alveoli and the atmosphere divided by the resistance The walls of the airways, especially the bronchioles, offer some resistance to the normal flow of air into and out of the lungs 25  Other Factors Affecting Pulmonary Ventilation Airway resistance As the lungs expand during inhalation, the bronchioles enlarge because their walls are pulled outward in all directions Airway diameter is also regulated by the degree of contraction or relaxation of smooth muscle in the walls of the airways Larger diameter airways have decreased resistance Airway resistance then increases during exhalation as the diameter of bronchioles decreases 26  Other Factors Affecting Pulmonary Ventilation Airway resistance Any condition that narrows or obstructs the airways increases resistance, so that more pressure is required to maintain the same airflow The hallmark of asthma or chronic obstructive pulmonary disease (COPD, emphysema or chronic bronchitis) is increased airway resistance due to obstruction or collapse of airways 27 Lung volumes and capacities 28  Lung volumes and capacities Tidal volume (TV): This is the amount of air which passes into and out of the lungs during each cycle of normal quiet breathing (about 500 mL). Inspiratory reserve volume (IRV): This is the extra volume of air that can be inhaled into the lungs during maximal inspiration Expiratory reserve volume (ERV): This is the largest volume of air which can be expelled from the lungs after maximal expiration Vital capacity (VC): This is the maximum volume of air which can be moved into and out of the lungs. VC = Tidal volume + IRV + ERV Residual volume: This can not be directly measured but is the volume of air remaining in the lungs after forced expiration. Functional residual capacity (FRC): This is the amount of air that can be inspired with maximum effort 29  Subtopics and learning outcomes Subtopics: 1. Physiology of the respiratory system Learning outcomes: Students should be able to: List the functions of the respiratory system Describe gas and pressure changes during pulmonary ventilation State the mechanism of respiration Name the muscles involved in respiration and accessory muscles of inspiration Describe intrapleural and intraplumonic pressure Describe the factors affecting pulmonary ventilation 30 Explain lung volumes and capacities Thank you! Have a great day! Questions? 31