Physiology 8th Lecture - Respiratory System

Gas pressures The air is a mix of gases Nitrogen Oxygen CO2 water vapor Inert gases Ar, Ne, Ze, Kr Atmospheric pressure 760 mm Hg Partial pressure Fraction of the total pressure (760 torr or mm Hg) Total pressure depends on, altitude, temperature... PP in the lungs is different than atmo due to gas exchange Intrapulmonary: intraalveolar pressure Intrapleural pressue Determined direction of air flow Physical aspect of ventilation Depends on lung volume. Physical properties that affect lung function: compliance, elasticity (elastic fibers cause recoil after respiration, can be harmed by scar tissue and so), surface tension (in premature newborns no surfactant, must be supllied artificialy. Ventilation Mechanical process to move air in and out of lungs. Driven by partial pressure. Vital capacity = total lung capacity – residual volume Cyclical variation Tidal volume FRC Minute ventilation Describe the ability to change the amount of oxy in the blood depends on tidal volume Normal is 7.5 L/min Alveolar ventilation V.E = Vt X f Vt = Vd + Va Anatomic dead space Volume of the lung not involved in gas exchange Mouth, pharynx, larynx trachea, bronchi

Alveolar dead space alveoli with no gas exchange Physiological dead space: ana +alveo dead space Partitioning minute ventilation Alveolar ventilation Dead space ventilation Factors determining alveolar PaCO2 Inspired air: no CO2 Increasing CO2 production: increases alveolar PaACO2 Increasing alveolar ventilation: decreases Muscles of respiration Inspiratory: External intercostal Parasternal intercostal Accesory mm Trapezious