Chapter 12 Book Notes PET3380CSurface Area and Gas Exchange• 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 exchangeAnatomy 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▪ bronchi - the large first generation airways that serve as primary conduits into each of the lungs◦ the bronchi further subdivide into numerous bronchioles that contain microscopic alveoli at the ends▪ bronchioles - ducts that conduct inspired air through a winding, narrow route until it eventually mixes with existing air in the alveolar ducts▪ alveoli - hollow terminal cavities that are spherical outcroppings of the respiratory bronchiolesLungs• 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 outThe Alveoli• the lung contains more than 600 million alveoli• alveoli - the final branching of the respiratory tree◦ 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• pores of Kohn - small pores within each alveolus◦ disperse surfactant over the respiratory membranes to reduce surface tension for easier 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 earlierMechanics of Ventilation• the ventilatory system in subdivided into two parts:◦ conducting zones (zones 1-16) - includes the trachea, primary bronchus, bronchus, the bronchi, and the bronchiolesChapter 12 Book Notes PET3380C▪ do not contain alveoli, so called “anatomic dead space”▪ function in:• air transport• humidification• warming• particle filtration• vocalization• immunoglobulin secretion◦ transitional and respiratory zones (zones 17-23) - bronchioles, alveolar ducts, and alveoli▪ 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• 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 volumeInspiration• 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 bodyExpiration• expiration - exhaling; moving air out of the lungs• 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 extensiveSurfactant• surface tension - a resisting force created at the surface of the lungs, for example, that has to be overcome for expansion to occurChapter 12 Book Notes PET3380C• surfactant - a wetting agent consisting of a lipoprotein mixture of phospholipids, proteins, and calcium ions produced by alveolar epithelial cells that reduces surface tensionStatic Lung Volumes• tidal volume (TV) - the air volume moved during either the inspiratory or expiratory phase of each breathing cycle (rest = 500-600mL)• inspiratory reserve volume (IRV) - the excess amount of air you can breath in after breathing in normally (rest = 1900-3000 mL)• expiratory reserve volume (ERV) - the amount of excess air that can exhaled after normal exhalation (rest = 800-1200 mL)• forced vital capacity (FVC) - maximum stroke volume of the lungs; the amount of air that can be exhaled after a maximal inspiration(rest = 3200-4800 mL)• inspiratory capacity (IC) - the amount of air that can be inspired after a maximal expiration (rest = 2400-3600 mL)• residual lung volume (RLV) - the amount of air left in the lungs after a maximal expiration (rest = 100-1200 mL)◦ increases with age◦ IRV and ERV decrease proportionallyEffects of Previous Exercise• RLV temporarily increases with short bouts of exercise and eventually returns to normal• this could be due to:◦ closure of the small peripheral airways◦ increase in thoracic blood volumeDynamic Lung Volumes• dynamic ventilation depends on two factors:◦ maximum “stroke volume” of the lungs (FVC)◦ speed of moving a volume of air (breathing rate)• lung compliance - measure of the ease of expansion of the lungs and thorax◦
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