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THE RESPIRATORY SYSTEM
Topics
• Parts of the respiratory system
• How the respiratory system works: breathing and gaseous exchange
• Tidal volume and vital capacity
• The effect of smoking
• Respiratory diseases
Introduction
First things first. Let’s clarify some concepts before we begin to study the respiratory
system.
Breathing refers to the ventilation or mechanical movement of the lungs (or gills). So, do
plants breathe?
Gaseous exchange refers to the diffusion of gases across a surface. So, is there a gaseous
exchange in plants?
Aerobic respiration is the breakdown of glucose in the presence of oxygen to obtain
energy. So, do plants respire?
So in order to supply the necessary oxygen to all our cells and remove the waste carbon
dioxide,
• we need the respiratory system during breathing, to obtain as much oxygen as
possible and get rid of carbon dioxide,
• we need gaseous exchange to take place in the lungs and
• we need the circulatory system to transport these gases to and from the lungs.
Parts of the respiratory system
And now, a brief description of the anatomy of our respiratory system.
From top to bottom we have:
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• Nasal cavity
• Bronchus (plural bronchi)
• Mouth cavity
• Bronchiole (plural bronchioles)
• Epiglottis
• Alveolus (plural alveoli)
• Larynx
• Diaphragm
• Trachea
Protecting the lungs (and heart) we have the ribs with intercostal muscles. The bronchioles
and alveoli are in what we call the lung, which is prevented from being damage by friction
against the ribs by the pleural membranes.
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Different parts have different functions:
The trachea or windpipe
The air passes into the lungs down a tube called the trachea. This is made up of rings of
cartilage.
There are plates of cartilage at the top of the trachea which widen at the point commonly
called the “Adam’s Apple”. This is in fact the larynx or “Voice Box”.
This is protected by a flap of skin called the epiglottis which closes when we swallow in
order to prevent food from going down the trachea.
Occasionally this doesn’t happen and we have all experienced feeling “choking” when food
goes down the wrong way.
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Bronchus, bronchiole and alveolus
At the bottom of the trachea we have two branches called the bronchi, through which air
passes into either lung.
Smaller and smaller branches, called bronchioles, extend out from the bronchi and at the
very ends of these they form tiny air sacs called alveoli. It is these that give the lungs their
spongy texture.
The bronchi and bronchioles also have cartilage but the alveoli don’t.
The linings of the alveoli are very thin and only work well when they are moist and clean.
When air is breathed in through the nose, it is:
1. FILTERED by the hairs at the entrance to the nose and by mucus.
2. WARMED by blood vessels passing close to the lining of the nose.
3. MOISTENED by water vapour.
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Special cells found in the respiratory system
There are certain cells that help keep the air clean and moist before it gets to the alveoli in
the lungs. These are the ciliated epithelial cells and the goblet cells.
Ciliated epitheial cell: sweep dust and bacteria away from lungs. The cilia act like the hairs
cilia
of a brush.
Goblet cells: secrete mucus to trap dust and bacteria.
For gaseous exchange to take place effortlessly, the surface must be kept clean. To ensure
this, there is another type of cell that removes whatever prevents an efficient gaseous
exchange in the lungs. These are the lung cleaners, the macrophages.
Macrophages: defense cells that attack any harmful particle or cell to prevent harm to the
lungs.
macrophages
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Breathing
The aim is to inhale as much oxygen possible to meet the cells demands and exhale carbon
dioxide.
When we BREATHE IN, the cycle starts with the ribs lifting upwards and outwards. This
is caused by the contraction of the intercostal muscles which are situated between the
ribs. There is also movement in the body as the diaphragm contracts, changing to a flatter
shape.
When we BREATHE OUT, the diaphragm relaxes, moving upwards back to a dome shape.
The ribs are pulled downwards and inwards. This is caused by the relaxation of the
intercostal muscles.
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Breathing Rate and respiratory volumes
The rate at which we inhale and exhale is controlled by the respiratory centre, within the
brain. Inspiration occurs due to increased firing of inspiratory nerves and so the increased
recruitment of motor neurons within the intercostal muscles and diaphragm. Exhalation
occurs due to a sudden stop in impulses along the inspiratory nerves.
Our lungs are prevented from excess inspiration due to stretch receptors within the bronchi
and bronchioles which send impulses to the brain when stimulated.
Breathing rate is all controlled by chemoreceptors within the main arteries which monitor
the levels of oxygen and carbon dioxide within the blood. If oxygen saturation falls,
ventilation accelerates to increase the volume of oxygen inspired, as occurs when running.
If levels of carbon dioxide increase a substance known as carbonic acid is released into the
blood which causes hydrogen ions (H+) to be formed. An increased concentration of H+ in
the blood stimulates increased ventilation rates. This also occurs when lactic acid is
released into the blood following high intensity exercise.
Respiratory volumes are the amount of air inhaled, exhaled and stored within the lungs at
any given time
Tidal Volume: represents the volume of air breathed in and out during a single breath. It is
the amount of air which enters the lungs during normal inhalation at rest. The average tidal
volume is 500ml. The same amount leaves the lungs during exhalation.
Inspiratory Reserve Volume: the amount of extra air inhaled (above tidal volume) during a
deep breath. This can be as high as 3000ml.
Expiratory Reserve Volume: the amount of extra air exhaled (above tidal volume) during a
forceful breath out.
Residual Volume: The amount of air left in the lungs following a maximal exhalation. There
is always some air remaining to prevent the lungs from collapsing.
Vital Capacity: represents the maximum volume of air that can be breathed in or breathed
out of the lungs. It is the most air you can exhale after taking the deepest breath you can. It
can be up to ten times more than you would normally exhale.
Total Lung Capacity: This is the vital lung capacity plus the residual volume and is the total
amount of air the lungs can hold. The average total lung capacity is 6000ml, although this
varies with age, height, sex and health.
So, during exercise, which one changes and how?
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In humans, the average rate of breathing dependent on age. As babies up to 6 weeks we
take 30 to 60 breaths per minute, while the average resting respiratory rate for adults is 12
to 20 breaths per minute. Physical exertion also has an impact on respiratory rate and
healthy adults can average 45 breaths per minute during strenuous exercise.
Speaking of which…
Activity! Calculate your breathing rate at rest and then have someone checking your
breathing rate immediately after jumping for 30 seconds and two minutes after exercise.
What happens?
(Source: http://www.livescience.com/22616-respiratory-system.html)
Try this:
http://www.teachpe.com/multi/relationship_cardiovascular_respiratory_system.htm
(cardiovascular and respiratory systems online quiz)
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Gaseous exchange
How the respiratory system and the circulatory system work together.
The main function of the respiratory system is gaseous exchange. This refers to the process
of oxygen and carbon dioxide moving between the lungs and blood.
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•
•
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Diffusion occurs when molecules move from an area of high concentration (of that
molecule) to an area of low concentration.
This occurs during gaseous exchange as the blood in the capillaries surrounding the
alveoli has a lower oxygen concentration of oxygen than the air in the alveoli which has
just been inhaled.
Both alveoli and capillaries have walls which are only one cell thick and allow gases to
diffuse across them.
The same happens with carbon dioxide (CO2). The blood in the surrounding capillaries
has a higher concentration of CO2 than the inspired air due to it being a waste product of
energy production. Therefore CO2 diffuses the other way, from the capillaries, into the
alveoli where it can then be exhaled.
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There are some requirements to ensure a fast and efficient gaseous exchange.
Respiratory surfaces must be:
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•
•
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Highly irrigated
Very large surface area
Very thin
Moistened
This is because the rate at which gases diffuse depends on three factors:
1. The thickness of the surface
2. The concentration of the gas on either side
3. The area of the surface
This is summarized in
FICK’S LAW OF DIFFUSION
It follows that the thinner and bigger a surface is, and the higher the difference in
concentration on both sides, the faster molecules will diffuse across it.
In the lungs, the partial pressure of oxygen in the alveoli is higher than the partial pressure
of oxygen in the capillaries (remember that the pulmonary artery and its branches carry
oxygen –poor blood from the heart to the lungs), so oxygen diffuses from the alveoli to the
red blood cells in the capillaries.
The reverse happens with the carbon dioxide: the partial pressure of carbon dioxide in the
capillaries is higher than the one in the alveoli, due to the reactions that take place in the
red blood cells. (Reread the transport of gases in blood in the CVS file if necessary).
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Respiratory diseases
Smoking affects our breathing and gaseous exchange, as cigarettes contain harmful
substances than can damage our respiratory system.
Some of the diseases related to smoking include:
• Chronic obstructive pulmonary disease (COPD) (including chronic bronchitis and
emphysema)
• Lung cancer and other types of cancer caused by smoking
healthy lungs versus smoker’s lungs
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Chronic bronchitis refers to an inflammation and blockage of the bronchi due to bacterial
infection. Cigarettes contain tar, which causes the cilia to stop beating so bacteria and other
particles accumulate. It also causes goblet cells to secrete more mucus as a response, so
during chronic bronchitis, the smoker frequently coughs to expel the phlegm that contains
mucus, bacteria and dust. Tar may also lead to lung cancer in the long term since it
promotes mutations in normal lung cells which may transform into tumor cells.
The alveoli have thin walls which contain elastin fibres. These allow the alveoli to recoil
(deflate) when we breathe out. When a person inhales cigarette smoke or certain other
irritants, this triggers the reaction of the defense cells, the lung macrophages. The immune
system responds by releasing substances that are meant to defend the lungs against the
smoke. These substances can also attack the cells of the lungs, but the body normally
inhibits such action with the release of other substances. Emphysema occurs when the
delicate alveolar walls are destroyed by the macrophages. Macrophages, in order to reach
the alveolus and eat away any harmful bacteria in it, release an enzyme (elastase) which
breaks down the elastic fibers surrounding the alveolus. After some years of smoking, the
alveolar elastin is destroyed and the alveoli can’t deflate much, eventually breaking. In
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smokers the lung tissue is damaged in such a way that it loses its elasticity. The small
passageways (bronchioles) leading to the alveoli collapse, trapping air within the alveoli.
The alveoli, unable to recoil efficiently and move the air out, over expand and break. This
reduces the rate of gaseous exchange since there is a smaller area of diffusion between
alveoli and capillaries. Smokers will then experience wheezing and breathlessness.
Smoking can also affect the circulatory system as cigarettes contain nicotine which
increases the stickiness of platelets, thus increasing the risk of thrombosis (blood clotting).
It also affects blood vessels as it triggers the release of the hormone adrenaline which will
stimulate the nervous system to reduce the diameter of arterioles. As a result, there is an
increase in blood pressure and heart rate and causes a drop in peripheral temperature
(hands and feet are much colder).
Carbon monoxide is another substance found in cigarette smoke. Carbon monoxide is a
poisonous gas that lowers the oxygen carrying capacity of the red blood cells.
Haemoglobin is the protein found in RBCs that combines with oxygen to carry it to all our
cells. Since haemoglobin has a greater affinity for carbon monoxide than it does for oxygen,
when carbon monoxide is present it will combine with haemoglobin instead of oxygen. As a
consequence, the smoker will feel tired and weaker as there is less oxygen available to
carry out aerobic respiration.
Other respiratory diseases, unrelated to smoking, are asthma, (an allergy) and respiratory
infections such as pneumonia, influenza and tuberculosis.
Asthma causes breathing difficulties due to inflammation of bronchi and bronchioles. This
causes a restriction in the airflow into the alveoli. The inflammation of the bronchioles is
allergy-related. An allergy is an exaggerated response of the immune system to a substance
(the allergen). Air pollution, tobacco smoke, factory fumes, cleaning solvents, infections,
pollens, foods, cold air, exercise, chemicals and medications are some common asthma
triggers.
Pneumonia: an infection caused by inhaling certain viruses or bacteria. Pneumonia is
usually characterized by fever, cough, and cutting chest pain. These lung infections are
treated with antibiotics or antivirals to which these bacteria and viruses are sensitive.
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Influenza (the flu): a virus that enters your body through your nose and mouth and causes
fever, headaches, muscle aches and sore throat. It is not treated with antibiotics, only rest
and keeping yourself warm, drinking plenty of liquid.
Tuberculosis (TB): a bacterial infection that attacks the lungs and other parts of the body
and can be deadly if not treated correctly.
Occupational lung disease: the lung is often injured by foreign substances that are inhaled
in the workplace. These diseases are varied and are caused by inhalation of gases as well
as particulate matter. (e.g. coal or minerals (silicosis), as in mines).
More information about respiratory diseases can be found at:
http://www.livescience.com/22616-respiratory-system.html)
http://www.medical-exam-essentials.com/respiratory-system-diseases.html
http://health.howstuffworks.com/diseases-conditions/respiratory/diseases-of-therespiratory-system.htm
http://nursingcrib.com/case-study/chronic-obstructive-pulmonary-disorder-copd-casestudy/
Lesson Summary
http://www.ck12.org/user:eWVvbWFubWlrZUBzYXlkZWwubmV0/section/TheRespiratory-System/
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Respiration is the process in which gases are exchanged between the body and the
outside air. The lungs and other organs of the respiratory system bring oxygen into the
body and release carbon dioxide into the atmosphere.
•
Respiration begins with ventilation, the process of moving air into and out of the lungs.
Gas exchange in the lungs takes place in across the thin walls of pulmonary arteries in
tiny air sacs called alveoli. Oxygenated blood is transported by the circulatory system
from lungs to tissues throughout the body. Gas exchange between blood and body cells
occurs across the walls of peripheral capillaries.
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•
Gas exchange helps maintain homeostasis by supplying cells with oxygen, carrying away
carbon dioxide waste, and maintaining proper pH of the blood.
•
Breathing occurs due to repeated contractions of a large muscle called the diaphragm.
The rate of breathing is regulated by the brain stem. It monitors the level of carbon
dioxide in the blood and triggers faster or slower breathing as needed to keep the level
within a narrow range.
•
Diseases of the respiratory system include asthma, pneumonia, and emphysema.
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