The Respiratory System
Breathing is something you do all day, every day – mostly without even thinking about it.
Respiratory System
 Is one of the major organ systems of the body.
 It is made up of the lungs, bronchi, trachea, and other structures.
The figure below shows air that enters through the mouth and nose and passes through the throat.
From there it travels through the trachea (windpipe), which divides into two branches called bronchi
(singular: bronchus)
The cells lining the trachea and bronchi are covered in cilia. The cilia are imbedded in a layer of mucus,
which traps bacteria and particles of dirt from the air. The cilia move together to sweep the mucus
upwards, away from the delicate tissues in the lungs.
Gas exchange
Air is a mixture of gases. Oxygen makes up about 21% of air by volume. The lungs absorb oxygen from
this mixture. How does this occur? Like a tree trunk that divides into smaller branches, bronchi branch
again and again, ending in tiny air sacs. Each sac is surrounded by a network of capillaries. Capillaries are
tiny, thin-walled blood vessels that are part of the circulatory system. Both the air sacs and the
capillaries are made up of a layer of epithelial tissue that is only one cell thick.
Oxygen Transport
Oxygen moves into the capillaries by diffusion. As you know, diffusion is the movement of a substance
from an area where it is more concentrated to an area where it is less concentrated. The air we breathe
into our lungs has a higher concentration of oxygen than the blood in the capillaries around the air sacs.
Therefore, the oxygen diffuses through the air sac and the capillary into the blood.
Removing Carbon Dioxide
Oxygen moves from the lungs into the blood, and the blood transports the oxygen to other parts of the
body. Here, oxygen diffuses out of the blood and into the body tissues. At the same time, carbon dioxide
diffuses from the tissues into the blood. Carbon dioxide is a waste gas produced by the body as the body
uses energy to move, grow, and repair itself. The blood carries carbon dioxide to the lungs. The carbon
dioxide diffuses from the blood into the air sac. The carbon dioxide is then released through the mouth
or nose when we breathe out. The taking in of oxygen and the releasing of carbon dioxide is called gas
exchange: our bodies exchange carbon dioxide for oxygen.
Breathing
The process of breathing involves alternately drawing air into the lungs (inhalation) and then pushing air
out (exhalation). Breathing uses muscles that move the ribs and the diaphragm, a large sheet of muscle
underneath the lungs. When the muscles and diaphragm relax, they move inward and air is pushed out
of the lungs. When the muscles and diaphragm contract, they move outward and air is pulled into the
lungs.
Control of Breathing
Some breathing is voluntary. Singers control their breathing in order to hold notes. Swimmers use
controlled breathing as they move their faces in and out of water. Mostly, though, breathing is
involuntary. We do not have to think about this function; our bodies simply do it. Though we can choose
to breathe in or hold our breath for a period of time, sensors in the brain cause the body to resume
involuntary breathing action after a short period of time. Give it a try! How long can you hold your
breath?
The brain controls breathing. When you hold your breath, carbon dioxide builds up in your blood.
Sensors in your circulatory system detect the increase of carbon dioxide. They send a signal to the brain.
In response, the brain sends messages to the diaphragm and to the muscles of the rib cage to contract.
The diaphragm flattens when it contracts. At the same time, muscles contract to raise the rib cage.
These movements expand the lungs and draw oxygen-rich air into them. Carbon dioxide can now leave
the blood, and more oxygen can enter it.
Respiratory Diseases
Diseases that reduce the flow of air into and out of the lungs are called chronic obstructive pulmonary
diseases (COPD). These diseases make it difficult to breathe, are often permanent, and may get worse
over time. The symptoms of these diseases are often made worse by air pollution. This is why the media
advise people with respiratory problems stay indoors on “bad air days”.
There are three main types of COPD: asthma, emphysema, and chronic bronchitis.
Asthma is a respiratory disease that involves airway swelling and mucus production. People with
asthma usually have periods of wellness between episodes.
Emphysema is another respiratory disease. With emphysema, the tiny air sacs in the lungs collapse and
the walls between them are destroyed. The surface area through which oxygen diffuses is smaller and
less oxygen can be picked up by the blood.
Chronic bronchitis is a respiratory disease in which tissues lining the airway become swollen. The
passageway for air is narrowed, causing coughing and breathlessness. As with emphysema, less oxygen
reaches body cells. Both emphysema and chronic bronchitis generally worsen over time.
Causes of Respiratory Disease
Your body needs to breathe clean air. Smokers and those exposed to second-hand smoke are at greater
risk of developing asthma, chronic bronchitis, and emphysema. Exposure to pollution is another risk
factor for respiratory disease. Recent studies show that exposure to chlorine in swimming pools can
increase your chance of getting asthma. You can protect the health of your respiratory system by not
smoking and avoiding being around others who smoke. Wear a respirator mask if you thing you will be
exposed to harmful materials in the air.
Questions
1. What parts compose the respiratory system?
2. Define the following terms: diffusion, cilia, and capillaries.
3. Describe the path oxygen takes when it enters the respiratory system.
4. What is the role of cilia in the respiratory system?
5. When you breathe in air, how much oxygen are you taking in?
6. Explain the process of how gases (oxygen, CO2) are exchanged in the respiratory system.
7. Describe how breathing can be both voluntary and involuntary.
8. How does the brain control your breathing?
9. Compare and contrast three types of respiratory disease.
10. Curare is a drug used by South American native hunters. It paralyzes the muscles of the animals they
hunt. How does this affect the animals’ ability to breathe?
11. Spaceships and submarines have technology on board to remove carbon dioxide from the air.
Explain why this technology is necessary.