Download Breath of Life Reading

Names: __________________________&_________________________ Date: _______________ Block: ___________
The Breath of Life
Story of the Human Respiratory System
Directions: Read and highlight text. Record all new vocab in journal. Then answer questions.
Take a nice, deep breath. Let it out slowly. What do you think happens in your body with
each breath that you take? Each time you breathe in, you draw air into your lungs. This action is
important for your survival because air contains oxygen (O2). Oxygen, as you may know, is a
substance that every cell of your body needs. Each time you breathe out, you expel air out of your
lungs. This action is also important because it helps rid your body of carbon dioxide. Carbon dioxide
(CO2) is a substance that is produced in cells as they transform the chemical energy in food into
other forms of usable energy.
The process of breathing requires a finely regulated interaction of a number of organ
systems. The organ system most directly involved in regulating your body’s interaction with the
atmosphere is the gas exchange system, also known as the respiratory system. The central organs of
the gas exchange system are the lungs. The lungs form two compartments that connect to the
outside environment through your trachea (windpipe) and your nose and mouth. The air inside
these lung compartments is not actually inside the internal environment of your body. Instead, the
tissues of the lungs themselves separate this air from the rest of the cells of your body.
How does oxygen move from your lungs into the internal environment of your body? And
how does carbon dioxide move from the internal environment back into your lungs and back into
the external environment? The answers involve a combination of simple chemical processes and
complex regulation to maintain homeostasis.
As you draw another deep breath, think about the path that the air must travel. The air
passes through the nose, which it is warmed, moistened, and cleaned. Sometimes the air passes
through the mouth instead. Then it enters the trachea and passes the vocal folds (vocal cords). The
trachea divides into smaller tubes called bronchi. Bronchi divide into even smaller branches. The
surfaces of these breathing tubes are lined with mucus-producing membranes and cilia. Cilia are
tiny, hair-like structures that move in a wavelike manner. They sweep debris out of the passages.
When the air finally reaches the ends of the passages in the lungs, it enters smaller compartments.
These smaller compartments are made up of many tiny air sacs called alveoli. In the two human
lungs, there are about 300 million alveoli. The pathway of air entering the lungs is shown in figure
5.17.
Once the oxygen is in the
alveoli, it is in the smallest lung
compartment. However, it has not
yet passed into the body’s internal
environment. To enter the internal
environment of the body, the oxygen
must diffuse across the alveoli’s thin
walls. You would have to stack about
200 alveoli walls to equal the
thickness of this page. These walls
are called alveolar membranes.
Names: __________________________&_________________________ Date: _______________ Block: ___________
The large number of alveoli increases the surface area of the lung tissue. In fact, the surface area of
the alveoli is 40 times greater than the entire outer surface of the human body (see figure 5.18).
The very high surface area increases the amount of oxygen that can move into the body’s internal
environment. It also increases the
amount of carbon dioxide that can enter
the lungs to be exhaled.
The movement of oxygen across the
alveolar membranes includes the
interaction of the gas exchange system
and the circulatory system. As shown in
figure 5.19, a system of capillaries filled
with blood surrounds each small group
of alveoli. This blood comes into such
close contact with the thin membranes
of the alveoli that simple diffusion
allows oxygen to enter the body. The
diffusion of oxygen depends on its
concentration in the air sacs and in the
blood inside the capillaries that
surround them. If the concentration of
oxygen is lower in the blood than in the
air sacs, the oxygen diffuses from the
air sacs into the blood. In the blood, the
oxygen binds to the protein
hemoglobin. Hemoglobin is found in the red blood cells. Through the flow of blood, oxygen is then
carried to all parts of the body. In this way, these two systems work together to deliver oxygen to
cells deep inside the body that have no direct contact with the outside environment.
At the same time that oxygen is diffusing into the blood, carbon dioxide is diffusing out of the
blood and into the alveoli. Carbon dioxide is released from cells that are transforming stored energy
into energy that they can use. Carbon dioxide is released from these cells and diffuses into the
blood. The blood carries carbon dioxide away from cells all over the body and delivers it to the
lungs. At the lungs, carbon dioxide diffuses across the alveolar membranes and goes into the air
inside the lungs. The concentration of carbon dioxide in the blood, and in the air inside the alveoli,
determines the direction of diffusion. Because the concentration of carbon dioxide is usually higher
Names: __________________________&_________________________ Date: _______________ Block: ___________
in the blood, carbon dioxide usually diffuses out of the blood and into the air inside the lungs. The
enormous surface area in the lungs speeds up the release of carbon dioxide from the blood into the
lungs. When you exhale, you release this carbon dioxide from your lungs into the external
environment around you.
Like many other homeostatic processes, breathing involves precise feedback systems.
Feedback occurs when outputs of a system are “fed back” as inputs as part of a chain of cause-andeffect that forms a circuit or loop. These feedback systems involve the gas exchange system,
circulatory system, and nervous system. Consider, for example, what happens to your breathing
rate during rapid exercise. As processes in the body speed up, the production of carbon dioxide also
increases. Carbon dioxide causes the blood to become more acidic. Sensory nerve cells in the brain
and in the arties such as the aorta, detect the increased acidity. These special cells send a signal to
the respiratory centers in the brain. The respiratory centers respond by stimulating the diaphragm
and rib muscles to contract more rapidly. Rapid contraction of these muscles increases the
breathing rate. A faster breathing rate increases the rate at which oxygen is brought into the body. A
faster breathing rate also increases the rate at which carbon dioxide is released from the body.
When you stop exercising, the rate of carbon dioxide production declines. The blood, then, becomes
less acidic. The change is detected by the sensory receptors in the blood vessels. The information is
relayed to the respiratory centers in the brain. Finally, signals are sent to the diaphragm and rib
muscles to contract more slowly. This regulatory system works automatically. You do not have to
control your breathing rate consciously. The signals involved are very powerful. Although you have
some control over your breathing rate, you cannot hold our breath indefinitely. Once the carbon
dioxide level in your blood reaches a critical level, the homeostatic signals override your efforts to
hold your breath and you are forced to exhale and take another breath.
Take on last deep breath. Can you describe what is happening your lung as you inhale and
exhale? Can you remember how the rate of your breathing is normally controlled? Now consider
this… because of several homeostatic systems, many important adjustments that you never have to
think about take place in you body. What is the evidence that this is going on? Think of all the little
breaths you took between those three nice, deep breaths.
FUN FACT: Hiccups
The “hic” of hiccups can at
times be caused by blockages
or lesions that crimp one of the
phrenic nerves, which control
breathing. These nerves are an
evolutionary “hand-me-down”
from frogs. The nerves relay
brain signals that induce a
spasm of muscles in the throat
and chest, causing the
epiglottis to shut the windpipe.
The sharp inspiration and
blocking of the threat, the “hic,”
are a legacy of a tadpole’s
pumping of water into its
mouth when breathing through
its gills. As it ingests water, its
glottis closes to prevent fluid
from entering its lungs, which
are used for breathing on land.
Names: __________________________&_________________________ Date: _______________ Block: ___________
1) Label the parts of the respiratory system, using the information given in the story.
2) Describe the basic processes of the human respiratory system, starting from when you
breathe in a gulp of air to when you eventually exhale.
Include all the words underlined in the first two pages of the above story.
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Names: __________________________&_________________________ Date: _______________ Block: ___________
3) In one paragraph, discuss diffusion and how it relates to oxygen/carbon dioxide exchange
in our respiratory system.
You can find this information on the second page, starting with the bolded words, “The movement
of oxygen across the alveolar membranes…”
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4) Why can you not hold your breath forever, despite how hard you try?
Write a detailed paragraph using the CER format (Claim, Evidence, Reasoning) to answer the
question. Your answer should include all of the underlined AND italicized words on the last page of
the above story.
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BONUS QUESTIONS (1 pt each):
1) Why do we hiccup? _________________________________________________________________________________________
2) This trait can be described as a _______________________ trait, because it is a remnant of our past and
is no longer needed. (Hint: Think- what type of structure is the appendix??)
3) Hiccups provide evidence for ________________________, because they show humans and frogs share a
_________________________________.