The Nose - Usually air will enter the respiratory system through the nostrils.
The nostrils then lead to open spaces in the nose called the nasal
passages. The nasal passages serve as a moistener, a filter, and to
warm up the air before it reaches the lungs. The hairs existing
within the nostrils revents various foreign particles from entering.
Different air passageways and the nasal passages are covered with
a mucous membrane. Many of the cells which produce the cells that
make up the membrane contain cilia. Others secrete a type a sticky
fluid called mucus. The mucus and cilia collect dust, bacteria, and
other particles in the air. The mucus also helps in moistening the air.
Under the mucous membrane there are a large number of capillaries. The
blood within these capillaries helps to warm the air as it passes
through the nose. The nose serves three purposes. It warms, filters,
and moistens the air before it reaches the lungs. You will obviously
lose these special advantages if you breath through your mouth.
Pharynx and Larynx - Air travels from the nasal passages to the pharynx, or more
commonly known as the throat. When the air leaves the pharynx
it passes into the larynx, or the voice box. The voice box is
constructed mainly of crtilage, which is a flexible connective
tissue. The vocal chords are two pairs of membranes that are
stretched across the inside of the larynx. As the air is exspired,
the vocal chords vibrate. Humans can control the vibrations of the
vocal chords, which enables us to make sounds. Food and liquids
are blocked from entering the opening of the larynx by the epiglottis
to prvent people from choking during swallowing.
Trachea - The larynx goes directly into the trachea or the windpipe. The trachea is
a tube approximately 12 centimeters in length and 2.5 centimeters wide.
The trachea is kept open by rings of cartilage within its walls. Similar
to the nasal passages, the trachea is covered with a ciliated mucous
membrane. Usually the cilia move mucus and trapped foreign matter to the
pharynx. After that, they leave the air passages and are normally swallowed.
The respiratory system cannot deal with tabacco smoke very keenly. Smoking
stops the cilia from moving. Just one cigarette slows their motion for
about 20 minutes. The tabacco smoke increases the amount of mucus in the
air passages. When smokers cough, their body is attempting to dispose of
the extra mucus.
Bronchi - Around the center of the chest, the trachea divides into two cartilage-ringed
tubes called bronchi. Also, this section of the respiratory system is lined
with ciliated cells. The bronchi enter the lungs and spread into a treelike
fashion into smaller tubes calle bronchial tubes.
Bronchioles - The bronchial tubes divide and then subdivide. By doing this their walls
become thinner and have less and less cartilage. Eventually, they become
a tiny group of tubes called bronchioles.
Alveoli - Each bronchiole ends in a tiny air chamber that looks like a bunch of grapes.
Each chamber contains many cup-shaped cavities known as alveoli. The walls of
the alveoli, which are only about one cell thick, are the respiratory surface.
They are thin, moist, and are surrounded by several numbers of capillaries.
The exchange of oxygen and carbon dioxide between blood and air occurs through
these walls. The estimation is that lungs contain about 300 million alveoli.
Their total surface area would be about 70 square meters. That is 40 times
the surface area of the skin. Smoking makes it difficult for oxygen to be
taken through the alveoli. When the cigarette smoke is inhaled, about
one-third of the particles will remain within the alveoli. There are too
many particles from smoking or from other sources of air pollution which can
damage the walls in the alveoli. This causes a certain tissue to form. This
tissue reduces the working area of the respiratory surface and leads to the
disease called emphysema.
