Volumes

Tidal Volume (TV) = volume of air during one resting respiratory cycle.

Expiratory Reserve Volume (ERV) = volume of air that can be forcefully expired, following a resting expiration.

Inspiratory Reserve Volume (IRV) = Volume of air that can be forcefully inspired, following resting inspiration.

Residual Volume (RV) = Volume of air that remains in lungs. About 1200mL.

Capacities

Vital Capacity (VC) = maximal amount of air that can be expired after maximal inspiration.VC = TV + IRV + ERV

Functional Residual Capacity (FRC) = Amount of air that remains in lungs following a relaxed expiration.FRC = ERV + RV

Total Lung Capacity (TLC) = Maximal volume of air in lungs.TLC = RV + ERV + TV + IRV or TLC = VC + RV

Inspiration.a. Relaxed inspiration. Diaphragm and external intercostal muscles contract.

b. Forceful inspiration. Diaphragm and external intercostal are supplemented by the sternocleidomastoid and pectoralis minor muscles.

Expiration. a. Normal expiration is due to elastic recoil of lungs and abdominal organs.

b. Forceful expiration is supplemented by the internal intercostal muscles and abdominal wall muscles.

Factors Affecting Breathing

1. Medullary Respiratory Center – detects changes in CO2 and H+ (pH) concentrations• Major Stimulus for breathing

2. Carotid Bodies & Aortic Bodies – detects changes in O2 concentrations

CO2 + H2O H2CO3 HCO3- + H+

Hering-Breuer Reflex: • Stretch receptors in lung tissues are stimulated during inspiration. • Sensory impulses travel via the vagus nerve to the pneumotaxic center of the respiratory

center in the pons. • Duration of inspiration shortens. Prevents overinflation.

CO2 + H2O H2CO3 HCO3- + H+