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 tothe 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 themouth 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.
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, andin the air inside the alveoli, determines the direction of diffusion. Because the concentration of carbon dioxide is usually higher 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-and-effect 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 diaphragmand 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 thinkabout 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.
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 underlinedin the first two pages of the above story.
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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 ______.