Exam 3 - Pulmonary Ventilation Flashcards
what parts of the respiratory tract are included in the conductive zone?
- bronchi
- bronchioles
- terminal bronchioles
fxn of the conductive zone
- bulk movement of air
- defensive role
(NO respiratory fxn)
what parts of the respiratory tract are included in the transitional/respiratory zone?
- respiratory bronchioles
- alveolar ducts
- alveoli
fxn of the transitional/respiratory zone
-sites for gas exchange
what is the functional unit of the lung?
acinus: terminal bronchiole, respiratory bronchioles, alveolar duct, and alveoli, and their circulation
describe how air velocity changes at each branch point, where there is an increase in surface area? what does this mean in terms of where diffusive gas movement begins?
Increase in SA leads to drastic decrease in velocity b/c in a closed system, (air velocity)(total airway area)/time must be equal at all points -> air velocity drops to almost zero in the acini
(for this reason, gas movement is primarily diffusive beginning at the terminal and respiratory bronchioles, whereas in the URT gas is moved by bulk flow)
what is total diffusion distance from alveolus to capillary lumen?
less than 0.5 um
what are the two main defensive functions of the respiratory tract?
- conditioning of inspired air
2. removal of debris
why do we need conditioning of inspired air?
- humidification and warming to prevent dessication of resp surface that could lead to infection
- filtration
how do we remove debris?
- mucous: suspends debris, protecting resp surfaces (only as far as terminal bronchioles)
- cilia: propel mucous suspension toward pharynx
- alveolar macrophages: phagocytic destruction of debris
- sneezing and coughing
what is the intrapleural space and its fxn?
liquid-filled area b/w visceral and parietal pleura - provides fluid coupling b/w the surfaces (slide easily against one another but resist being pulled apart)
why is the intrapleural pressure slightly negative and the intrapulmonary pressure zero?
recoil force of chest wall and diaphragm just balance the lung’s tendency to collapse, leading to these pressures
what does air in the intrapleural space cause?
pneumothorax
what structures are responsible for inspiration?
quiet: diaphragm (75%), external intercostals
forced: same + scalenes and SCM
how do the actions of the inspiratory structures cause inspiration?
expansion of chest lowers intrapleural pressure, making intrapulmonary pressure sub-atmospheric -> pressure differentials cause air to flow toward alveoli
why do very small pressures suffice to move large amounts of air?
b/c of the large cross-sectional area of the LRT, and therefore the very low total resistance to flow
what structures are responsible for expiration?
quiet: passive - due to recoil of elastic elements of lung
forced: abdominal muscles
equation for respiratory resistance
Rtotal = Rpulmonary + Rthoracic
what pathology can cause an increase in respiratory resistance?
- increased blood/fluid in lungs/pulm fibrosis -> increase in pulmonary resistance
- diseases of rib cage and diaphragm/ increased intra-abdominal volume -> increased thoracic resistance
what is surface tension?
mutual attraction of water molecules at an air-water interface that tends to minimize the area of the interface
what is lung compliance?
the change in lung volume for a given change in pressure (deltaV/deltaP)
relationship between surface tension and compliance in the lung
surface tension at the alveolar air-water interface favors collapse of alveoli (aka it decreases lung compliance)
how does the body compensate for the fact that surface tension/compliance favor collapse of alveoli?
surfactant (phospholipid of dipalmitoyl phosphatidylcholine + 4 proteins) - dramatically lowers tension relative to water + induces an area-dependent effect on tension
(increase in film area = increase in tension and vice versa -> compliance is never compromised - actually increases compliance by reducing work required to expand lung - causes decreased tension to compensate for increased pressure of a smaller radius)
describe surfactant production
- starts at 32 weeks gestation
- under influence of cortisol
premies often have surfactant deficiency and need to be put on positive pressure ventilators
