2. Anatomy : Resp. Tract
• One of the most important problems in all the respiratory passages is
to keep them open to allow easy passage of air to and from the
alveoli
• Trachea – with cartilage rings 5/6 of the way around
• Bronchi – walls have less extensive cartilage plates
• Bronchioles – no plates. Diameter <1.5mm, all smooth muscles
Kept expanded by same transpulmonary pressures that expand the alveoli
3. Anatomy: Pulmonary Circulatory System
• Pulmonary artery (5 cm, thin, 1/3 aorta)
• Right and Left main pulmonary branches – lungs
• Large compliance (7 mL/mmHg)
• Allows pulmonary arteries to accommodate 2/3 of stroke volume output of
Right Ventricle
• Bronchial Vessels – arterial supply to the lungs
• 1/3 of cardiac output
• Supplies supporting tissues
• Drains to pulmonary veins
4. Pulmonary vs. Alveolar Ventilation
• Pulmonary Ventilation
• Inflow and outflow of air between the atmosphere and the lung alveoli
• Alveolar Ventilation
• Rate at which new air reaches the areas in the lung where it is in proximity to
the pulmonary blood or gas exchange areas (alveolar sacs, ducts, respiratory
bronchioles)
5. Diffusion of Gases
Resp. tract Alveoli Pulmonary blood
• All the gases of concern in respiratory physiology and in the fluids and tissues of
the body are simple molecules that are free to move among one another by
diffusion
• Random molecular motion of molecules with energy provided by kinetic motion of
the molecules
• All molecules are continually undergoing motion except in absolute zero
temperature
• Net diffusion
Product of diffusion from high to
low concentration
