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5.
Secretions (FYI)
a.
Surfactant
The alveoli are hollow spaces lined with water diffusing out
from the tissue. This is similar to the air spaces in the
center of a leaf. As you recall, the surface tension of
water in those air spaces is sufficient to pull water up the
xylem column. That much force would make it difficult to
expand the alveoli during inhalation. Surfactants are
proteins that reduce surface tension and make it possible to
breath. Lack of surfactant in the lungs of premature infants
causes respiratory distress syndrome and is a major cause of
death.
b.
Mucus
Some of the lung epithelial
cells also produce a sticky protein goo (mucus) that
captures dirt and germs in the lungs. The mucus is cleared
out of the respiratory system by the beating of cilia on
airway cells. Smoking can immobilize the cilia, leading to a
buildup of mucus.
C.
Bird lungs42.24
- air moved through the
lungs in a unidirectional manner We
will not describe these in detail. The most important
general feature is
thatair is moved
through the lungs in a unidirectional manner.
Q.
Why is this important?
- the fresh air coming in is not mixed with
O2-depleted
air, so the concentration of
O2in
the lungs is the same as outside air. This increases the
concentration difference
between air and lungs, thus increasing transfer.
This is
the reason why birds can fly over rainbows and Mt. Everest
where humans need oxygen tanks.
Note:
there is a mistake in Figure 42.19; try to spot
it.
(Campbell,
4th, mid. 836- mid 843
Note: there is a mistake in Figure 38.18; try to spot it.
)
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