Efficient gas exchange can only occur if the alveoli are regularly flushed with fresh air.
Diaphragm: a muscle connected to the bottom of the lungs
Pleura: a membrane that connects the lungs to the walls of the chest cavity
INHALATION:
Mechanism > external intercostals plus the diaphragm contract to bring about inspiration
intercostals elevate ribs & sternum
increases dimension of thoracic cavity
lowers air pressure in lungs and air moves into lungs
diaphragm pulls lungs downward
increases dimension of thoracic cavity
lowers air pressure in lungs and air moves into lungs:
EXHALATION:
Mechanism > external intercostals plus the diaphragm relax to bring about exhalation
intercostals ribs, & sternum to resting position
decreases dimension of thoracic cavity
increases pressure in lungs and air is exhaled
diaphragm lungs move upward
decreases dimension of thoracic cavity
increase air pressure in lungs and air is exhaled
Breathing is the cyclic repetition of inhalation and exhalation
delivers oxygen to the alveoli and removes carbon dioxide
Lung Volumes and Vital Capacity
Tidal Volume (TV):
is the volume of air moved in and out of the respiratory tract (breathed) during each breath; about 0.5 L
Inspiratory Reserve Volume (IRV)
is the additional volume of air that can be forcibly inhaled following a normal inspiration;
about 2.5-3.5 L
Expiratory Reserve Volume (ERV)
is the additional volume of air that can be forcibly exhaled following a normal expiration; about 1.0 L
Vital Capacity (VC)
is the maximal volume of air that can be forcibly exhaled after a maximal inspiration. VC = TV + IRV + ERV; about 4.5 L
Residual Volume (RV)
is that volume of air remaining in the lungs after a maximal expiration. It cannot be expired no matter how vigorous or long the effort. RV = FRC – ERV; about 1.0 L
Functional Residual Capacity (FRC)
is the volume of air remaining in the lungs at the end of a normal expiration. FRC = RV + ERV
Total Lung Capacity (TLC)
is the volume of air in the lungs at the end of a maximal inspiration
TLC = FRC + TV + IRV = VC + RV; about 6 L
Anatomical dead space
is the air in the respiratory airways that is unavailable for gas exchange; about 0.150 L
