Page 138 - Biology Form Two

Biology for Secondary Schools

the external intercostal muscles contract muscles relax while the internal
while the internal intercostal muscles intercostal muscles contract, pulling
relax and pull the rib cage upward and the ribcage inward and downward.
outward, as shown in Figure 6.2. These As a result, the volume of the thorax
movements result to an increase in the decreases and the pressure inside it
LungREADING ONLY
volume and decrease in the air pressure increases. This forces air out through
of the thorax. This process makes air the bronchioles, bronchus, trachea, and

flow into the lungs through the nostrils, nostrils.
trachea, bronchus, bronchioles, and

alveoli.

Air exhaled Ribs move inward

Air inhaled
Ribs
Ribs move
outward Lung
Ribs
FOR ONLINE
Diaphragm

Diaphragm Figure 6.3: Exhalation

Differences between inhalation and
Figure 6.2: Inhalation
exhalation
Exhalation The processes of inhaling and

Exhalation helps to remove carbon exhaling gases in human beings can
dioxide gas from the body. Carbon be differentiated based on the changes
dioxide is a cellular waste product. that occur in the parts of the respiratory
During exhalation, the muscles of the system such as the ribs, intercostal
diaphragm relax and the diaphragm muscles, and diaphragm. Table 6.4
resumes its dome shape, as shown in summarises the differences between
Figure 6.3. The external intercostal inhalation and exhalation.

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