PET3380C Chapter 12 Book Notes Surface Area and Gas Exchange bronchi the lungs the ends bronchioles the basal metabolic requirement to supply the muscles is 2 to 4 L per minute ventilatory system the system that regulates the gaseous state of the body s external pulmonary environment to effectively aerate body fluids meets the requirements for gas exchange Anatomy of Ventilation pulmonary ventilation the process of moving and exchanging ambient air air outside with air in the lungs air entering the nose and mouth flows into the conductive portions of the ventilatory system where it adjusts to body temperature and is filtered and almost completely humidified as its travels through the trachea trachea windpipe connects pharynx and larynx to lungs air conditioning continues as inspired air passes into two bronchi the large first generation airways that serve as primary conduits into each of the bronchi further subdivide into numerous bronchioles that contain microscopic alveoli at ducts that conduct inspired air through a winding narrow route until it eventually mixes with existing air in the alveolar ducts bronchioles alveoli hollow terminal cavities that are spherical outcroppings of the respiratory they provide the gas exchange surface separates the blood from the surrounding alveolar gaseous environment oxygen transfers from alveolar air into alveolar capillary blood while the blood s carbon dioxide moves into the alveolar chambers where it flows into ambient air ie oxygen is taken in and carbon dioxide is pushed out Lungs The Alveoli the final branching of the respiratory tree the lung contains more than 600 million alveoli alveoli elastic and thin but strong composed of simple squamous epithelial cells provide surface for gas exchange between lung tissue and blood receives the largest blood supply of any of the body s organs disperse surfactant over the respiratory membranes to reduce surface tension for easier small pores within each alveolus pores of Kohn alveolar inflation also provide for gas interchange between adjacent alveoli for each minute at rest about 250 mL of oxygen leaves the alveoli and enters the blood while about 200 mL of carbon dioxide diffuses in the opposite direction this was mentioned earlier Mechanics of Ventilation the ventilatory system in subdivided into two parts conducting zones zones 1 16 bronchi and the bronchioles do not contain alveoli so called anatomic dead space function in air transport includes the trachea primary bronchus bronchus the Chapter 12 Book Notes PET3380C transitional and respiratory zones zones 17 23 bronchioles alveolar ducts and alveoli humidification warming particle filtration vocalization immunoglobulin secretion respiratory zone is the site of gas exchange occupies about 2 5 to 3 L constitutes largest portion of the total lung volume function in surfactant production molecule activation and inactivation blood clotting regulation endocrine function Inspiration Fick s Law of Diffusion states that a gas diffuses through a sheet of tissue at a rate directly proportional to the tissue area a diffusion constant and the pressure differential of the gas on each side of the membrane and inversely proportional to tissue thickness the lungs actually adhere to the chest wall and literally follow its every movement therefore any change in the thoracic cavity volume correspondingly alters the lung volume diaphragm large dome shaped sheet of striated musculofibrous tissue that creates an airtight separation between the abdominal and thoracic cavities contains a series of opening through which the esophagus blood vessels and nerves pass inspiration breathing in the diaphragm muscle contracts flattens and moves downwards toward the abdominal cavity the chest cavity elongates enlarges and expands the air in the lungs causing its intrapulmonic pressure to decrease to slightly below atmospheric pressure intrapulmonic pressure the pressure within the lung tissue during inspiration the scaleni and external intercostal muscles between the ribs contract causing the ribs to rotate and lift up and away from the body exhaling moving air out of the lungs expiration this results from two factors natural recoil of the stretched lung tissue relaxation of the inspiratory muscles during strenuous exercise internal intercostal and abdominal muscles act powerfully on the ribs and abdominal cavity to reduce thoracic dimensions ie makes exhaling more rapid and extensive a resisting force created at the surface of the lungs for example that has to be surface tension overcome for expansion to occur surfactant calcium ions produced by alveolar epithelial cells that reduces surface tension a wetting agent consisting of a lipoprotein mixture of phospholipids proteins and Static Lung Volumes tidal volume TV each breathing cycle rest 500 600mL inspiratory reserve volume IRV in normally rest 1900 3000 mL the air volume moved during either the inspiratory or expiratory phase of the excess amount of air you can breath in after breathing Expiration Surfactant the amount of excess air that can exhaled after normal maximum stroke volume of the lungs the amount of air that can PET3380C the amount of air that can be inspired after a maximal expiration the amount of air left in the lungs after a maximal expiration Chapter 12 Book Notes rest 3200 4800 mL expiratory reserve volume ERV exhalation rest 800 1200 mL forced vital capacity FVC be exhaled after a maximal inspiration inspiratory capacity IC rest 2400 3600 mL residual lung volume RLV rest 100 1200 mL increases with age IRV and ERV decrease proportionally Effects of Previous Exercise this could be due to closure of the small peripheral airways increase in thoracic blood volume Dynamic Lung Volumes RLV temporarily increases with short bouts of exercise and eventually returns to normal dynamic ventilation depends on two factors maximum stroke volume of the lungs FVC speed of moving a volume of air breathing rate lung compliance determined by the pulmonary volume and elasticity measure of the ease of expansion of the lungs and thorax how much a person can exhale during a forced breath FEV to FVC Ratio forced expiratory volume FEV depends on resistance to air movement pulmonary expiratory power Maximum Voluntary Ventilation maximum voluntary ventilation MVV repetitive maximal effort training illustrates a drastic increase in MVV volume of air expired in a specified period during Exercise Implications of Gender
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