BIOL 1104 Lecture Notes - Partial Pressure, Cardiac Output, Exhalation

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11 Feb 2013
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Overview of Lung Function
I. Purpose of Respiratory System
a. Provide tissues w/ O2 while removing wastes (CO2)
b. Entire cardiac output passes thru lungs => body attempts to match airflow
into lungs w/ O2 delivery to tissues
c. Terms
i. Perfusion—oxygen delivery to tissues
ii. Ventilation—airflow into lungs
iii. Minute ventilation—amount of air in/out of lungs per minute; ~
5L/min
II. Structure/Function
a. Conduction takes place in the airways (convective)
i. Smaller cross sectional area, high flow
b. Diffusion takes place in alveoli (smallest airways)
i. Huge cross sectional area, very little flow
c. Air/blood interface
i. Active side—very thin (<0.5 um); efficient gas exchange
1. alveolar epithelium → interstitial space → capillary
endothelium
ii. Service side—thicker barrier between air & capillary; contains
important “scaffolding” (connective) tissues of lung; tends to be
the site of pathogenic accumulation of fluids
III. Partial Pressures of Gases
a. Ptot = ∑ each gases’ partial pressure
b. Partial pressure (Px) = Ptot X fractional concentration (Fx)
i. Fractional concentrations of gases remain constant at different
altitudes, but Ptot decreases => less inspired O2!
c. Must take PH2O into account as well!
i. At 37 C, PH2O = 47 mmHg (fully saturated)
d. In alveoli, must also take PCO2 into account
in ambient air FCO2 is too small to be relevant
IV. Lung Volumes & Capacities
a. Terms
i. Volume—amount of gas that cannot be broken down into smaller
components
ii. Capacity—made up of more than 1 volume (eg: TLC = RV + TV
+ IRV)
b. Relevant Terms
i. Functional Residual Capacity (FRC)—balance between chest
wall’s desire to open and lung’s desire to collapse; amount of air in
lungs after expiring a normal breath
ii. Tidal Volume (TV)—size of a single (normal) breath
iii. Total Lung Capacity (TLC)—total amount of air that fits in lungs;
TLC = RV + VC
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