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

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