Respiratory Physiology and

Lung Capacity

Inhalation

• Diaphragm contracts

• Ribs move up and out, chest cavity enlarges and pressure decreases

• Air rushes in from higher pressure environment

Exhalation

• Diaphragm relaxes

• Ribs compress, chest cavity gets smaller and pressure increases

• Air escapes to lower pressure environment

Breathing

• Involuntary inhalation and exhalation

• Delivers O2 to alveoli and removes CO2

• Medulla oblongata– Brain region that controls

breathing

Gas Exchange

Control of Breathing

• Chemoreceptors detect change in blood pH

– Blood high in CO2 has lower than normal pH

• Drop in pH causes medulla oblongata to stimulate breathing

Breathing is aNegative Feedback

Loop

Human Lung Capacity

• Influenced by many factors:– Age– Gender– Body position– Strength of diaphragm– Strength of chest muscles– Illness / disease

• The average human breathes 12-20 times per minute.

Measurements

Tidal Volume (TV): the amount of air inhaled and exhaled in a normal breath.

Inspiratory Reserve Volume (IRV): the amount of air that can be inhaled after a normal inhalation.

Expiratory Reserve Volume (ERV): the amount of air that can be forcefully exhaled after a normal exhalation.

Vital Capacity (VC): the maximum amount of air that can be exhaled. (VC = TV + IRV + ERV)

Residual Volume (RV): the amount of air remaining in the lungs after a forceful exhalation.

Without this “leftover” air in our lungs, they would collapse!

Average Lung Volumes for Young Adult Males

Measuring Lung Capacity

• Displacement Method

– Air is breathed through a tube into a bottle of water.

– Air displaces the water (water leaves the bottle into the surrounding tub).

– Litres of air are measured from markings on side of bottle.

Measuring Lung Capacity

• Balloon Method– Air is breathed into

balloon.– Circumference (C) of

balloon is measured.– Volume is calculated

with the following formula:

€

V =1

6×1

π 2×C3

Measuring Lung Capacity

• Spirometer– Air is breathed into the

mouthpiece of the spirometer.

– The spirometer’s gauge needle moves.

– The gauge’s measurement is read in mL.

Comparing Average Lung Capacities

• Males tend to have larger vital capacities than females.

• Athletes and musicians tend to have larger VC.

• Smokers tend to have a smaller VC.

How do we measure up to other mammals?