Like every other system of the body, the respiratory system is very
complex, with a number of interdependent parts. It begins with the
nasal passages of the nose (and mouth in some cases), the pharynx,
the epiglottis, the trachea, the bronchial tubes, the bronchioles, and
the alveoli. And don't let us forget the diaphragm.
The preferred method of breathing is through the nose. This is
because the surface of the nasal cavity contains many tiny blood
vessels; heat from these blood vessels warms the air that you breathe.
Special cells in the nasal cavity add moisture. Tiny hairs also filter out
small specks of dirt.
The air is then passed through the throat (pharynx) to the
windpipe (trachea). Since for a short while both air and food follow
the same path, the windpipe has a small flap of tissue called the
epiglottis. Without the epiglottis food could be trapped in the windpipe
and result in suffocation. The windpipe then divides into two passages
called the bronchial tubes, which carry the air to each lung. The
bronchial tubes are lined with cilia, small hair-like protrusions that
move in a wave-like motion. These cilia force phlegm and dirt
particles upward into the throat where they can be coughed up or
swallowed.
The bronchial tubes further divide into tiny passages called
bronchioles that lead to millions of tiny sacs in the lungs called alveoli.
There are so many alveoli in the lungs that when a lung is dissected, it
looks very much like a sponge. The alveoli are absolutely essential to
proper breathing, since they tremendously expand the lungs' capacity
to get oxygen to the blood stream.
Imbedded in the lining of each alveolus are tiny blood vessels
called capillaries. When oxygen reaches the alveoli, it passes through
the walls of the capillaries and into the blood stream, where it is
carried to cells throughout the body. At the same time, carbon dioxide
collected in the blood stream because of bodily activities passes
through the capillary walls into the alveoli, where it is expelled from
the body when we exhale.
We cannot forget the diaphragm, a flat muscle that is located
just below the lungs. In addition to separating the upper body cavity
(the thoracic cavity) from the lower, abdominal cavity, the diaphragm
performs an absolutely essential function in respiration. When the
diaphragm contracts, the volume of the lungs expands and air
pressure in them goes down. Since the air pressure is then greater on
the outside of your body, the air comes rushing into the lungs
(inhalation).
On the other hand, when the diaphragm expands, your lung
capacity goes down and the air pressure in the lungs goes up. Now
the pressure is higher inside than outside, and the air goes rushing out
(exhalation). All of this goes on without your having to think about it.
It is regulated by the brain through a complicated process.
Now, the question is, what could man or a supposed ancestor of
man have done without while evolving the respiratory system? As was
mentioned before, without the epiglottis, food would get trapped in the
bronchial tubes, causing suffocation. The alveoli are also absolutely
essential to allow us to breathe in enough oxygen with each breath to
sustain life. And we certainly could not do without the diaphragm that
enables us to inhale and exhale. Evolutionists have no explanation as
to how the lungs could have gradually evolved. The lungs are yet
another example of the irreducible complexity that is so ubiquitous in
nature.