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The Respiratory System
THE FUNCTION OF RESPIRATION
RESPIRATION AND GAS EXCHANGE
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Most of the cells of your body need a continual supply of oxygen (O2) to carry out cellular respiration.
This process releases energy from glucose inside cells and produces carbon dioxide as a waste product.
The resulting chemical energy is used to perform cellular activities.
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The main function of the RESPIRATORY SYSTEM is to ensure that oxygen is brought into the body
and made available to each cell that needs it, and that carbon dioxide can leave each cell and be removed from the
body.
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RESPIRATION is the general term that is used to describe this overall process.
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The first stage in respiration – breathing, involves two basic processes:
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There are several stages in human respiration, and each stage has specialized structures to facilitate it.
INSPIRATION – the action of
drawing oxygen-rich air into the lungs, and EXPIRATION – the action of releasing waste air from the lungs.
Inspiration moves air from outside the body into the lungs. Expiration moves air from the lungs back to the
outside of the body.
The second stage in respiration – external respiration, is the exchange of oxygen and carbon dioxide between
the inspired air inside the lungs and the blood. This stage of the respiratory process performs the vital function of
gas exchange. GAS EXCHANGE is the delivery of oxygen from the lungs to the blood, and the
elimination of carbon dioxide from the blood to the lungs.
The third stage in respiration – internal respiration, is the exchange of oxygen and carbon dioxide between the
blood and the body’s tissue cells.
The fourth and final stage in respiration – cellular respiration, which is a series of energy-releasing chemical
reactions that take place within the cells. It is the sole means of providing energy for all cellular activities.
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RESPIRATORY SURFACES
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There are two main requirements for respiration. First, the area of an animal’s body where gases are exchanged
with the environment, called its respiratory surface, must be large enough for the exchange of oxygen and
carbon dioxide to occur quickly enough to meet the body’s needs. Second, respiration must take place in a moist
environment, so that the oxygen and carbon dioxide are dissolved in water.
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To increase the efficiency of respiration, all organisms use VENTILATION which is the process of moving
an oxygen-containing medium (water or air) over the respiratory surface (such as gills, trachea, or lungs).
Some animals, like the earthworm, do not have specialized gas exchange organs. They use their entire outer
skin as a respiratory surface. Oxygen diffuses into a network of thin-walled capillaries just below the skin, and
carbon dioxide diffuses out.
Fish and many aquatic invertebrates (clams, mussels, crayfish, crabs) exchange gas through gills. Gills are
extensions or folds in the body surface tha increase the surface area through which gases are exchanged. Oxygen
in the water diffuses across the gill surfaces into capillaries, and carbon dioxide diffuses out into the external
environment.
Insects exchange gases through a tracheal system. This is an internal system of branching respriatory tubes called
tracheae. The tracheae connect body cells directly to the environment outside the insect’s body by even smaller
tubes called spiracles.
Most land animals require much more oxygen than could be delivered by gills or a tracheal system. Mammals,
birds, reptiles, and most amphibians exchange gases through an internal respiratory system consisting of a trachea
(or windpipe) that branches into lungs.
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GAS EXCHANGE IN AQUATIC ENVIRONMENTS
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Aquatic environments contain oxygen in the form of dissolved oxygen.
Many aquatic animals, such as fish, lobsters, clams, and molluscs, take in oxygen through gills.
Gills are physical adaptations that enable organisms to carry out gas exchange in aquatic environments.
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A fish exchanges gases by taking water into its mouth and ventilating (or pumping) it over the gills. As water
flows across the gills, dissolved oxgen in the wter diffuses into the blood circulating thorugh the surrounding
capillaries. At the same time, carbon dioxide from the blood diffuses across the gill tissue into the water.
Another adaptation used by fish is a counter-current exchange mechanism. Blood flows through the gills in the
opposite direction to the flow of oxgyen-containing water. Oxygen diffuses along a gradient, called a
DIFFUSION GRADIENT, meaning that the oxygen molecules move from a region of high concentration
to a region of low concentration. Because blood and water flow in opposite directions, the diffusion gradient of
the oxygen is kept high.
GAS EXCHANGE ON LAND
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Air breathing vertebrates, such as reptiles, birds, and mammals, rely on lungs for gas exchange.
In air-breathing vertebrates, the respiratory system is a specialized system that provides a passageway for air to
move from outside the body to inside the body, where gas exchange occurs.
Air does not flow into and out of the lungs on its own. The brain acts as a respiratory control centre to coordinate breathing movements and regulate the breathing rate. It also monitors the volume of air in the lungs and
the gas levels in the blood.
Two sets of structures – the diaphragm and the rib muscles – control the air pressure inside the lungs.
Changes in air pressure cause air to move into and out of the lungs.
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The DIAPHRAGM is a dome-shaped layer of muscle that separates the region of the lungs (the
thoracic cavity) from the region of the stomach and liver (the abdominal cavity).
 The rib muscles, or intercostal muscles, are found between the ribs and along the inside surface of the rib
cage.
With regular signals from the brain, the diaphragm and the intercostal muscles work together at the same time to
move air into and out of the lungs.
Inhalation begins when the external intercostal muscles and the diaphragm contract, and the diaphragm moves
down. This action expands the rib cage upward and outward, and the floor of the chest cavity moves downward.
Since the chest cavity is air tight, its volume increases. The increase in volume means that the same amount of air
is contained in a larger space. When the molecules of a gas are far apart, as they are when the volume of the chest
cavity increases, the gas molecules exert less outward pressure. As a result, the air pressure in the thoracic cavity
decreases.
The lungs are suspended in the chest cavity and are sensitive to changes in the air pressure of the cavity. As the
air pressure in the cavity decreases, the walls of the lungs are drawn outward into the chest cavity and the lungs
expand. This expansion causes the air pressure in the lungs to be lower than the air pressure outside the body.
Since air moves from regions of higher pressure to regions of lower pressure, air rushes into the lungs form the
external environment.
The opposite muscle movements expel air from the lungs. Exhalation begins when the diaphragm and the rib
muscles relax. This reduces the volume of the chest cavity. Therefore, the volume of the lungs decreases, and the
air pressure inside the lungs increases. This will move air from the lungs to the lower-pressure environment
outside the body.
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Respiratory Volume
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Your breathing rate after physical exertion is faster than your normal breathing rate.
Under normal circumstances, your regular breathing does not use the full capacity of your lungs.
When your body needs more oxygen, the volume of air that is drawn into your lungs will increase.
THE SPIROGRAPH
 A SPIROGRAPH is a graph representing the amount (volume) and speed (rate of flow) of air that is inhaled
and exhaled, as measured by a spirometre. It represents the air the moves into and out of the lungs with each
breath. A Spirograph has the following features:
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TIDAL VOLUME – the volume of air that is inhaled and exhaled in a normal breathing movement
when the body is at rest.
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INSPIRATORY RESERVE VOLUME – the additional volume of air that can be taken into
the lungs beyond a regular, or tidal, inhalation.
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EXPIRATORY RESERVE VOLUME – the additional volume of air that can be forced out
of the lungs beyond a regular, or tidal, exhalation.
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Total Lung Volume Capacity – is the total volume of gas that
can be moved into or out of the lungs. It can be calculated as tidal volume + inspiratory reserve volume +
expiratory reserve volume.
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RESIDUAL VOLUME – the amount of gas that remains in the lungs and the passageways of the
VITAL CAPACITY – also called:
respiratory system even after a full exhalation. This gas never leaves the respiratory system; if it did, the
lungs and the respiratory passageways would collapse. The residual volume has little value for gas
exchange because it is not exchanged with air from outside the body.
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The Human Respiratory System: A Closer Look
THE PASSAGE OF AIR THROUGH THE UPPER RESPIRATORY TRACT
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Air enters the respiratory system through the nostrils. Air can also enter through the mouth – especially if
breathing is rapid, as it is during strenuous exercise.
Inside the nasal passages at the back of the nose, air is warmed, moistened, and cleansed of dust and other small
particles.
Very thin bones, called turbinate bones, project into the nasal passages and increase the surface area of these
chambers. A thin membrane covering the turbinate bones secretes mucus, which moistens the air and traps
particles of dust, bacteria, and other foreign matter. The ciliated cells that are found in the membrane have
waving, hair-like projections that move the trapped particles into the nose or throat where they can be expelled by
sneezing or coughing.
The warm, moist, cleaned air passes from the nasal passages through the pharynx, or throat. At the base of the
PHARYNX (the passageway just behind the mouth that connects the mouth and nasal cavity to the larynx and
esophagus), behind the tongue, is the entrance to the TRACHEA (or windpipe – is the tube that carries air
from the nasal passages or mouth to the bronchi and then to the lungs). This opening of the trachea though which
air enters is called the GLOTTIS. The glottis can be closed by the epiglottis. The epiglottis is normally
upright to allow air to pass freely into the trachea. When you swallow food, the epiglottis covers the glottis to
prevent fod from entering the trachea and passing into the lungs.
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Between the glottis and the trachea, air passes through the LARYNX (or voicebox – which contains the vocal
cords). This structure is made of cartilage, which is a tough, firm connective tissue. They larynx is used for
sound production in mammals. The vocal cords consist of two folds of membrane stretches across the larynx.
During normal breathing, muscular tissue holds the vocal cords apart, allowing air to pass freely through the
larynx. To make sounds, the vocal cords are moved closer together so that pressure from air expelled from the
lungs causes the cords to vibrate. The pitch of the sound varies with the length of the vocal cords.
A long cord produces a low sound, and a short cord produces a higher sound At puberty, the vocal cords of males
grow quickly, which often causes a “breaking” quality in the voice.
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THE LOWER RESPIRATORY TRACT
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The two tubes that branch from the trachea to the lungs are called BRONCHI (singular: bronchus). One
bronchus enters each lung.
In humans, the lungs are divided into regions called lobes. The right lung has three lobes, and the left lung has 2
lobes (leaving space for the heart in the thoracic cavity).
Each lung is surrounded by a thin, flexible, double-layered sac, called the pleural membrane. The outer layer
of this membrane is attached to the inside of the chest wall, and the inner layer covers the lungs. The thin space
between these two layers contains a lubricating fluid that allows the layers to easily slide against each other
during the movements of breathing.
Inside the lungs, each bronchus subdivides many times to form a network of microscopic tubules called
BRONCHIOLES.
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Each bronchiole eventually ends in a grape-like cluster of tiny sacs called ALVEOLI
(singular: alveolus). Respiratory gases are exchanged in this sac.
There are an estimated 500 million alveoli in an average-sized adult human lung.
Surrounding each alveolus is a network of fine capillaries.
The walls of the alveoli and the walls of the capillaries are only one cell thick.
It is across these very thin membranes that the respiratory system and the circulatory system interact – as oxygen
from the air diffuses into the blood and carbon dioxide from the blood diffuses into the lungs.
GAS EXCHANGE IN HUMANS
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During external respiration, the thin walls of the alveoli and the capillaries allow gases to easily diffuse through
their cell membranes.
The air that enters the alveoli after inhalation has a higher concentration of oxygen than the blood in the
capillaries next to the lungs. As a result, oxygen diffuses out of the alveoli into the blood in the capillaries.
The blood in the capillaries has a higher concentration of carbon dioxide than the air in the alveoli because the
blood that diffuses into the capillaries is returning from the body tissue cells.
Remember, that the blood transports oxygen and nutrients to the cells. The oxygen and the nutrients diffuse into
each cell. Then, carbon dioxide and other wastes diffuse from the cells into the blood. This is why the capillaries
have higher concentrations of carbon dioxide when it reaches the lungs. So, the carbon dioxide diffuses into the
alveoli from the capillaries. The carbon dioxide is then exhaled into the air.
Once oxygen and carbon dioxide have been exchanged between the capillaries and the alveoli, the blood in the
capillaries begins its journey back to the heart and then on to all the tissue cells. There, oxygen diffuses from the
blood into the tissue cells and is exchanged for carbon dioxide once again.
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HOW BLOOD TRANSPORTS RESPIRATORY GASES
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During respiration, both oxygen (O2) and carbon dioxide (CO2) are transported via the bloodstream.
About 99% of O2 that reaches cells is carried by hemoglobin. The remaining 1% of O2 is dissolved in the water
blood plasma.
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HEMOGLOBIN is an iron-containing protein found in red blood cells (RBC) which binds to and transports
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oxygen from the lungs to the rest of the body.
When CO2 leaves the tissue cells and diffuses into the capillaries, it enters the red blood cells.
About 23% of CO2 is carried in the blood by hemoglobin. The remaining CO2 (77%) is carried in the blood
fluids.
When CO2 reaches the lungs, it diffuses into the air in the alveoli and is exhaled.
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Respiratory System Disorders
DISORDERS OF THE UPPER RESPIRATORY TRACT
1. TONSILLITIS
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TONSILLITIS is a bacterial or viral infection of the tonsils (two oval-shaped organs located in the pharynx
at the back of the throat).
The function of the tonsils is to help prevent bacteria and other harmful substances from entering the respiratory
system.
Symptoms of tonsillitis include red and swollen tonsils, a sore throat, fever, and swollen glands in the neck.
Tonsils tend to be naturally large in children and shrink as the child ages.
Severe tonsillitis may be treated by surgically removing all or part of the tonsils. However, removing tonsils can
increase the risk of throat infections later in life.
2. LARYNGITIS
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LARYNGITIS is an inflammation of the larynx caused by an infection or allergy, or by overstraining the
voice, such as by prolonged yelling.
Remember that the larynx contains the vocal cords. So, when the larynx is inflamed, the vocal cords cannot
vibrate as they usually do.
People with laryngitis may “lose” their voice, or speak in a hoarse whisper.
This condition is usually not serious and clears up on its own after a few days.
DISORDERS OF THE LOWER RESPIRATORY TRACT
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Several serious lower respiratory disorder can damage the bronchi and lungs.
The Public Health Agency of Canada estimates that over 3 million Canadians of all ages are affected by chronic
respiratory diseases.
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There are several main causes of respiratory disorders. Some are caused by exposure to infectious pathogens,
such as viruses, bacteria, and fungi. The other main cause is exposure to air pollutants that block parts of the
respiratory tract, obstucting the airflow or impeding the exchange of gases.
1. PNEUMONIA
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PNEUMONIA is disease that causes inflammation in one or both lungs.
It is caused by a viral infection or a
bacterial infection.
Pneumonia interferes with gas exchange, and the body becomes stared for oxygen.
There are two main types of pneumonia: lobular pneumonia (which affects the lobe of the lung), and bronchial
pneumonia (which affects patches throughout both lungs).
The main causes are bacterial infections and viral infections.
Lobular pneumonia is caused by the bacterium Streptococcus pneumoniae. This bacterial infection can spread out
of the lungs, by way of the bloodstream, and affect other tissues. There is a preventative vaccine, called the
pneumococcalvaccine, which provides long-term protection from the bacterium.
Viral pneumonias are usually less severe than bacterial pneumonias, and they can be treated with anti-viral
medications. Viral pneumonias may be followed by a secondary bacterial infection. This secondary infection
must be treated separately with antibiotics.
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2. BRONCHITIS
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BRONCHITIS is a respiratory disease that causes inflammation of the mucous membranes of the bronchi.
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is classified as either acute (due to an infection) or chronic (due to an irritant).
With bronchitis, the bronchi become red, inflamed, and filled with mucus, which the person expels by coughing.
Short-term bronchitis (acute) is usually caused by a bacterial infection and can be treated with antibiotics.
Chronic bronchitis is long-term disorder caused by regular exposure to concentrations of dust or chemical
compounds (often in the workplace), or cigarette smoke. Because the exposure takes place over a long period of
time, the cilia lining the bronchi are gradually destroyed.
Without the cleansing action of the cilia, the bronchi grow increasingly inflamed and vulnerable to infection.
Mucus accumulates in the bronchi, causing the person to develop a persistent cough in an attempt to clear it.
Chronic bronchitis is referred to as a chronic obstructive pulmonary disease (COPD), and is one of a few lung
diseases that is usually caused by smoking. COPD cannot be cured, but in can be treated by quitting smoking,
taking medications, and gently exercising.
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3. ASTHMA
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ASTHMA is a lung disease that causes chronic inflammation of the lungs and overproduction of mucus in the
lungs.
Inhaled irritants such as pollen, dust, and smoke can often trigger an inflammation of the bronchi and bronchioles.
The inflammation narrows the air passages of the bronchi and bronchioles, thus reducing airflow.
People with asthma experience wheezing, coughing, tightness in the chest, and shortness of breath.
During an asthma attack, muscles around the airways contract and cells in the airways may increase mucus
production, which further blocks airflow.
Asthma often starts in childhood. Although it cannot be cured, it can be managed.
Many people who have asthma use a hand-held inhaler – a device that delivers medication deep into the lungs.
Asthma medicaitons act by relaxing the bronchiole muscles and reducing inflammation, therefore, opening up the
airways.
4. EMPHYSEMA
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EMPHYSEMA is a chronic respiratory disease that affects the ability of the lungs to expel air.
Emphysema entails the walls of the alveoli losing their elasticity. This loss of elasticity reduces the respiratory
surface for gas exchange and causes an oxygen shortage in the tissues.
Exhaling becomes difficult because the small airways collapse during exhalation, trapping air in the lungs and
blocking the airflow.
The most common cause of this condition is smoking.
Emphysema is also classified as a COPD. It is not curable, although the symptoms can be relieved by using an
inhaler to open up the bronchioles and a low-flow oxygen tank to boose the supply of oxygen to the body.
5. CYSTIC FIBROSIS
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CYSTIC FIBROSIS is a genetic disease that causes a thick build-up of mucus in the lungs, resulting in
infection, inflammation, and damage to the lung tissues.
The mucus traps disease-causing agents, making it difficult to clear bacteria that cause lung infections.
The mucus also blocks the ducts of the pancreas, preventing digesting enzymes from reaching the intestines to
digest food.
There is no cure for cystic fibrosis, but symptoms can be relieved by medications that thin the mucus and
antibiotics that reduce bacterial infections.
The lack of the normal protein (from the mutated version of this particular gene) causes cells to secrete the extra
thick, sticky mucus.
Newer methods of gene therapy are being tested, using sprays, nose drops, or capsules, to deliver the unmutated
gene to cells lining the airways to the lungs. Tiny bubbles (called liposomes) in the sprays and drops contain
DNA without the cystic fibrosis mutation. The bubbles fuse with the outer surfaces of the cells that line the
airways. The DNA passes through the membranes into the cells. The added DNA instructs the cells to make the
essential protein lacking in people who have cystic fibrosis.
LUNG CANCER
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Lung cancer is a disease in which uncontrolled cell growth and division occurs in the lungs.
As the lung cells continue to grow and dividde in an uncontrolled way, they can create a rapidly growing mass of
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cells tha form a tumour, or CARCINOMA (a tumour made up of rapidly multiplying cells).
Carcinomas can grow as large as 8 cm, significantly reducing the respiratory surface of the lungs.
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Cancerous cells can also break away from a tumour and travel, therefore spreading cancer to other parts of the
lungs and to other organs and tissues.
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The spread of cancer from its original site is called METASTASIS. The cancerous cells that spread are
called metastatic cells.
Because lung tissues are located deep within the thoracic cavity, lung cancer is difficult to detect in its early stages
and difficult to treat.
Symptoms include a persistent cough, difficulty breathing, chest pain, and loss of appetite.
An X-ray of the chest does not show the presence of tumours until they are already quite larege and beginning to
spread.
About 80% of people die within 5 years of diagnosis, making lung cancer the leading cause of cancer deaths for
men and women in Canada.
The main cause of lung cancer is smoking tobacco, since tobacco smoke is a carcinogen (a cancer-causing agent).
Lung cancer can also be caused by persistent exposure to: second-hand smoke or other pollutants in the air, the
radioactive gas radon (naturally found in some rocks and soils and can enter buildings through cracks in the
foundations), asbestos (a fibrous, heat-resistant mineral once commonly used as insulation in buildings and in
brake linings).
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DIAGNOSING RESPIRATORY SYSTEM DISORDERS
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The main tool used to detect serious respiratory system disorders, such as lung cancer, is a specialized X-ray
technique called COMPUTED AXIAL TOMOGRAPHY (CAT or CT scan).
During a CT scan, the person lies on a special bed while a rotating X-ray device takes multiple images of the body
through 360 degrees. These images are processed by a computer to produce a complete set of cross-sectional
pictures of the body’s interior, including the soft tissue, bone, and blood vessels.
Spiral CT scanning is a newer technology that was developed in the mid-1980’s – the scanner continuously
rotates around the body in a spiral path. It produces more clear and detailed views.
TWO-PHOTON MICROSCOPY (TPM) is an imaging technology that uses special microscopes
that emit photons (particles of light) to penetrate samples of biologcial tissue. It can produce a 3-D image of cells
in the body wthout having to physically extract a sample.
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BRONCHOSCOPY (also known as bronchial endoscopy) is a technique for viewing, diagnosing, and
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treating the tissues and organs of the respiratory system. While patients are under general anesthesia, the doctor
inserts the bronchoscope through the mouth or nose and down into the lungs. Special attachments to the
bronchoscope allow to the doctor to take samples of mucus and tissue for biopsy, remove tumours, and repair
damaged blood vessels.
Bronchoscopy is also used to diagnose asthma.
TECHNOLOGIES FOR TREATING LUNG CANCER
 There are 3 main techniques for treating lung cancer: radiation, chemotherapy, and surgery.
 All treatments involve either killing or removing cancerous cells.
 The choice of treatment depends partly on the type and extent of the cancer and the age and health of the patient.
 Radiation therapy uses X-rays and other types of radiation to destroy cancer cells. It can be given externally or
internally for lung cancer. The most common type of external therapy is delivered by high-dose radiation form a
machine. Sometimes, radiation is delivered internally, through a thin plastic tube inserted into the lungs during
bronchoscopy. A small amount of radioactive material is passed through the plastic tube right to the site of the
cancer.
 Chemotherapy is treatment in which drugs that destroy cancer cells are either taken by mouth or injected into the
body. Chemotherapy is used in more advanced stages of cancer. The drugs work by stopping or slowing the
growth of cells that are dividing rapidly. However, chemotherapy drugs can also harm healthy cells that divide
quickly, such as cells in the skin, the mouth, and the digestive tract. As a result, chemotherapy often causes side
effects such as loss of hair, nausea, and mouth sores.
 Lung surgery involved removing the area of the lung that contains tumours. This may involve a small part of the
lung, a lobe of the lung, or an entire lung. If all the cancerous cells are successfully removed, the person will be
free of cancer. If some metastatic cells remain in the body, the cancer may begin to spread again after the
operation.
 Laser surgery involves using lasers to destroy lung tumours, which helps to reduce the damage to the lungs,
minimizing scarring, and speeds up the healing process. A laser emits a high-energy beam of light that can be
precisely focused on the tumour with minimal impact on surrounding tissues.
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