The Respiratory System Major Functions o Gas exchange between air and circulating blood o Moving air from the exchange surface of the lungs o Protection of respiratory surfaces o Production of sound o Provision for olfactory sensations Lung respiratory and conducting zones Respiratory zone respiratory bronchioles alveolar ducts sacs Conducting zone bronchioles bronchi trachea Alveoli have largest cross sectional area Bronchioles have smooth muscle cartilage 23 divisions of branches into ever smaller conduits Mucous secreting ciliated cells line conducting zone airways Large particles stop at nose smaller ones caught in cilia finest particles make it into alveoli Gas exchange can be divided into four functional components o Ventilation movement of air into lungs need pump to generate flow pipes slow down flow o Perfusion movement and distribution of blood through pulmonary circulation o Diffusion movement of O2 and CO2 across air blood barrier or alveolar capillary membrane o Control of breathing process of regulation of gas exchange to meet metabolic needs of moment Respiratory Regulation Pulmonary Ventilation o Movement of air into and out of the lungs so that the gases there are continuously changed and refreshed External Respiration Internal Respiration lungs blood Transport of Respiratory Gases o Movement of oxygen from the lungs to the blood and of CO2 from the blood to the o Movement of O2 from blood to the tissue cells and of CO2 from tissue cells to the o Transport of O2 from the lungs to the tissue cells of the body and of CO2 from the tissue cells to the lungs Mechanics of breathing Breathing or pulmonary ventilation consists of two phases Inspiration air flows into the lungs Expiration gases exit the lungs Pressure relationships in the thoracic cavity Breathing or pulmonary ventilation consists of two phases Inspiration air flows into the lungs Expiration gases exit the lungs Muscles Used During Inhalation Diaphragm external intercostals fibers of muscle running up in between ribs scalenes sternocleidomastoid Muscles used During Exhalation Internal intercostals fibers running down in between ribs rectus abdominus external oblique internal oblique and transversus abdominis See Picture 1 at end of document Pulmonary ventilation or breathing exchanges gases between the outside air and the alveoli of the lungs Ventilation which is mechanical in nature depends on a difference between the atmospheric air pressure and the pressure in the alveoli When we expand the lungs to inhale we increase internal volume and reduce internal pressure Physical factors influencing pulmonary ventilation airway resistance Friction is the major nonelastic source of resistance to airflow Airway resistance eg more resistance if bronchioles are narrowed in asthma The more resistance the less pulmonary ventilation can be achieved o Lung Compliance how much bounce back or recoil force there is from the lung eg Emphysema has too little recoil force and have problems exhaling So there is a balance of forces here o Alveolar surface tension the little border between liquid and air in your alveoli The oxygen in the air must get across the membrane to be absorbed by the blood vessels in your alveoli The greater the surface tension the harder it is for the oxygen to get into the blood example in some newborns they don t have a certain chemical surfactant to reduce surface tension and consequently can t breathe They need treatment with a surfactant on the lung tissue So the greater the surface tension the lower the pulmonary ventilation See Picture 2 at end of document Respiratory volumes and capacities We have a normal amount of air that we breathe in and out when we are at rest This normal amount of air is our tidal volume of air typically around 500 mL or a half of a liter This maximal amount of air that we can take in and breathe out is called our vital capacity It is approximately 3 liters Throughout a normal day we really never use our entire vital capacity We take our tidal volume of air in and then out throughout the entire day And whenever we are active or speaking we take in and let out more air than the tidal volume Even when we breathe out as much as we possibly can we can never eliminate all of the air from our respiratory tracts The absence of air is a vacuum and that cannot exist within us a vacuum would cause our respiratory tract to buckle in on itself Therefore there is always bit of air that we can never exhale approximately 1200 mL 1 2 liters of air in our respiratory system all the time This 1200 mL of air that remains in our respiratory tracts is called the residual volume Yet we do not usually even exhale enough air to leave only a residual volume of air Instead we normally only exhale through our tidal volume levels so all the air that we could choose to exhale plus the residual volume normally remains in our respiratory tracts after a resting exhalation this amount of air residual expiratory reserve is called the functional residual capacity See Picture 3 at end of document Dead space and alveolar ventilation dead space is air that is inhaled by the body in breathing but does not take part in gas exchange Not all the air in each breath is able to be used for the exchange of oxygen and carbon dioxide Alveolar dead space alveoli that are ventilated but not perfused There is normally no alveolar dead space Alveolar ventilation the amount of air that reaches the alveoli and is available for gas exchange with the blood per unit time Gas exchange ventilation breathing The process of gas exchange has several steps The following is a summary of the steps interchange of CO2 and O2 between air in the lungs alveoli and blood in lung capillaries by diffusion transport of CO2 and O2 through the bloodstream interchange of CO2 and O2 between blood in lung capillaries and alveolar air by diffusion use of O2 and production of CO2 by cells through metabolism o o o o o Ventilation The transfer of oxygen from the atmosphere to the tissues starts with the inspiration of air into the lungs The lungs consist mainly of tiny air containing alveolar sacs The alveoli connect to the larger terminal bronchioles of the airways The air adjacent to the surfaces of the alveolar wall are lined by a single cell layer of flat epithelial cells type I alveolar cells In between these type I cells are thicker and more rounded type II alveolar cells which produce a detergent like fluid In the alveolar walls the fluid and
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