About the Lungs and Respiratory System
Breathing is so vital to life that it happens automatically.
Each day, you breathe about 20,000 times, and by the time
you're 70 years old, you'll have taken at least 600 million
breaths.
All of this breathing couldn't happen without the
respiratory system, which includes the nose, throat, voice box,
windpipe, and lungs.
At the top of the respiratory system, the nostrils (also called
nares) act as the air intake, bringing air into the nose, where
it's warmed and humidified. Tiny hairs called cilia protect the
nasal passageways and other parts of the respiratory tract,
filtering out dust and other particles that enter the nose through
the breathed air.
Air can also be taken in through the mouth. These two openings
of the airway (the nasal cavity and the mouth) meet at the pharynx,
or throat, at the back of the nose and mouth. The pharynx is part
of the digestive system as well as the respiratory system because
it carries both food and air. At the bottom of the pharynx, this
pathway divides in two, one for food (the esophagus, which leads to
the stomach) and the other for air. The epiglottis, a small flap of
tissue, covers the air-only passage when we swallow, keeping food
and liquid from going into the lungs.
The larynx, or voice box, is the uppermost part of the air-only
pipe. This short tube contains a pair of vocal cords, which vibrate
to make sounds. The trachea, or windpipe, extends downward from the
base of the larynx. It lies partly in the neck and partly in the
chest cavity. The walls of the trachea are strengthened by stiff
rings of cartilage to keep it open. The trachea is also lined with
cilia, which sweep fluids and foreign particles out of the airway
so that they stay out of the lungs.
At its bottom end, the trachea divides into left and right air
tubes called bronchi, which connect to the lungs. Within the lungs,
the bronchi branch into smaller bronchi and even smaller tubes
called bronchioles. Bronchioles end in tiny air sacs called
alveoli, where the exchange of oxygen and carbon dioxide actually
takes place. Each lung houses about 300-400 million alveoli. The
lungs also contain elastic tissues that allow them to inflate and
deflate without losing shape and are encased by a thin lining
called the pleura. This network of alveoli, bronchioles, and
bronchi is known as the bronchial tree.
The chest cavity, or thorax, is the airtight box that houses the
bronchial tree, lungs, heart, and other structures. The top and
sides of the thorax are formed by the ribs and attached muscles,
and the bottom is formed by a large muscle called the diaphragm.
The chest walls form a protective cage around the lungs and other
contents of the chest cavity. Separating the chest from the
abdomen, the diaphragm plays a lead role in breathing. It moves
downward when we breathe in, enlarging the chest cavity and pulling
air in through the nose or mouth. When we breathe out, the
diaphragm moves upward, forcing the chest cavity to get smaller and
pushing the gases in the lungs up and out of the nose and
mouth.
What the Lungs and Respiratory System Do
The air we breathe is made up of several gases. Oxygen is the
most important for keeping us alive because body cells need it for
energy and growth. Without oxygen, the body's cells would
die.
Carbon dioxide is the waste gas produced when carbon is combined
with oxygen as part of the energy-making processes of the body. The
lungs and respiratory system allow oxygen in the air to be taken
into the body, while also enabling the body to get rid of carbon
dioxide in the air breathed out.
Respiration
Respiration is the set of events that results in the exchange of
oxygen from the environment and carbon dioxide from the body's
cells. The process of taking air into the lungs is inspiration, or
inhalation, and the process of breathing it out is expiration, or
exhalation.
Air is inhaled through the mouth or through the nose. Cilia
lining the nose and other parts of the upper respiratory tract move
back and forth, pushing foreign matter that comes in with air (like
dust) either toward the nostrils to be expelled or toward the
pharynx. The pharynx passes the foreign matter along to the stomach
to eventually be eliminated by the body. As air is inhaled, the
mucous membranes of the nose and mouth warm and humidify the air
before it enters the lungs.
When you breathe in, the diaphragm moves downward toward the
abdomen, and the rib muscles pull the ribs upward and outward. In
this way, the volume of the chest cavity is increased. Air pressure
in the chest cavity and lungs is reduced, and because gas flows
from high pressure to low, air from the environment flows through
the nose or mouth into the lungs. In exhalation, the diaphragm
moves upward and the chest wall muscles relax, causing the chest
cavity to contract. Air pressure in the lungs rises, so air flows
from the lungs and up and out of respiratory system through the
nose or mouth.
Every few seconds, with each inhalation, air fills a large
portion of the millions of alveoli. In a process called diffusion,
oxygen moves from the alveoli to the blood through the capillaries
(tiny blood vessels) lining the alveolar walls. Once in the
bloodstream, oxygen gets picked up by the hemoglobin in red blood
cells. This oxygen-rich blood then flows back to the heart, which
pumps it through the arteries to oxygen-hungry tissues throughout
the body. In the tiny capillaries of the body tissues, oxygen is
freed from the hemoglobin and moves into the cells. Carbon dioxide,
which is produced during the process of diffusion, moves out of
these cells into the capillaries, where most of it is dissolved in
the plasma of the blood. Blood rich in carbon dioxide then returns
to the heart via the veins. From the heart, this blood is pumped to
the lungs, where carbon dioxide passes into the alveoli to be
exhaled.
Problems of the Lungs and Respiratory System
The respiratory system is susceptible to a number of diseases,
and the lungs are prone to a wide range of disorders caused by
pollutants in the air.
The most common problems of the respiratory system are:
Asthma
. More than 20 million people in the United States have asthma, and
it's the #1 reason that kids chronically miss school. Asthma is
a chronic inflammatory lung disease that causes airways to tighten
and narrow. Often triggered by irritants in the air such as
cigarette smoke, asthma flares involve contraction and swelling of
the muscles lining the tiny airways. The resulting narrowing of the
airways prevents air from flowing properly, causing wheezing and
difficulty breathing, sometimes to the point of being
life-threatening. Management of asthma starts with an asthma
management plan, which usually involves avoiding asthma triggers
and sometimes taking medications.
Bronchiolitis
. Not to be confused with bronchitis, bronchiolitis is an
inflammation of the bronchioles, the smallest branches of the
bronchial tree. Bronchiolitis affects mostly infants and young
children, and can cause wheezing and serious difficulty breathing.
It's usually caused by specific viruses in the wintertime,
including
respiratory syncytial virus (RSV)
.
Chronic obstructive pulmonary disease
(COPD).
COPD is a term that describes two lung diseases - emphysema and
chronic bronchitis:
- Long-term smoking often causes
emphysema
, and although it seldom affects kids and teens, it can have its
roots in the teen and childhood years. Talking to your kids about
smoking is a key part of preventing smoking-related diseases. In
emphysema, the lungs produce an excessive amount of mucus and the
alveoli become damaged. It becomes difficult to breathe and get
enough oxygen into the blood.
- In
bronchitis
, a common disease of adults and teens, the membranes lining the
larger bronchial tubes become inflamed and an excessive amount of
mucus is produced. The person develops a bad cough to get rid of
the mucus. Cigarette smoking is a major cause of chronic
bronchitis in teens.
Other Conditions
Common cold
. Caused by over 200 different viruses that cause inflammation in
the upper respiratory tract, the common cold is the most common
respiratory infection. Symptoms may include a mild fever, cough,
headache, runny nose, sneezing, and sore throat.
Cough
. A cough is a symptom of an illness, not an illness itself. There
are many different types of cough and many different causes,
ranging from not-so-serious to life-threatening. Some of the more
common causes affecting kids are the common cold, asthma,
sinusitis, seasonal allergies, croup, and pneumonia. Among the most
serious causes of cough are tuberculosis (TB) and whooping cough
(pertussis).
Cystic fibrosis (CF)
. Affecting more than 30,000 kids and young adults in the United
States, cystic fibrosis is the most common inherited disease
affecting the lungs. Affecting primarily the respiratory and
digestive systems, CF causes mucus in the body to be abnormally
thick and sticky. The mucus can clog the airways in the lungs and
make a person more vulnerable to bacterial infections.
Lung cancer.
Caused by an abnormal growth of cells in the lungs, lung cancer is
a leading cause of death in the United States and is usually caused
by smoking cigarettes. It starts in the lining of the bronchi and
takes a long time to develop. Symptoms include a persistent cough
that may bring up blood, chest pain, hoarseness, and shortness of
breath. Radon gas exposure (radon is a gas that occurs in soil and
rocks) may also be a cause of lung cancer. Radon is more likely to
occur in certain parts of the United States. You can check your
home's radon level by purchasing a radon kit at your local home
supply or hardware store.
Pneumonia
. This inflammation of the lungs usually occurs because of
bacterial or viral infection. Pneumonia causes fever and
inflammation of lung tissue, and makes breathing difficult because
the lungs have to work harder to transfer oxygen into the
bloodstream and remove carbon dioxide from the blood. Common causes
of pneumonia are
influenza
and infection with the bacterium
Streptococcus pneumoniae
.
Pulmonary hypertension.
This condition occurs when the blood pressure in the arteries of
the lungs is abnormally high, which means the heart has to work
harder to pump blood against the high pressure. Pulmonary
hypertension may occur in children because of a heart defect
present at birth or because of a health condition such as HIV
infection.
Respiratory diseases of newborns.
Several respiratory conditions can affect a newborn baby just
starting to breathe for the first time.
Premature babies are at increased risk for conditions such
as:
-
Respiratory distress syndrome of the newborn.
Babies born prematurely may not have enough surfactant in the
lungs. Surfactant helps to keep the baby's alveoli open;
without surfactant, the lungs collapse and the baby is unable to
breathe.
-
Apnea of prematurity (AOP)
. Apnea is a medical term that means someone has stopped
breathing. Apnea of prematurity (AOP) is a condition in which
premature infants stop breathing for 15 to 20 seconds during
sleep. Apnea of prematurity generally occurs after 2 days of life
and up to a week of life. The lower the infant's weight and
level of prematurity at birth, the more likely the baby is to
have AOP spells.
-
Bronchopulmonary dysplasia (BPD)
. BDP involves abnormal development of lung tissue. Sometimes
called chronic lung disease or CLD, it's a disease in infants
characterized by inflammation and scarring in the lungs. It
develops most often in premature babies who are born with
underdeveloped lungs.
Other Respiratory Conditions in Newborns
-
Meconium aspiration
. Meconium aspiration occurs when a newborn inhales (aspirates) a
mixture of meconium (baby's first feces, ordinarily passed
after birth) and amniotic fluid during labor and delivery. The
inhaled meconium can cause a partial or complete blockage of the
baby's airways.
-
Persistent pulmonary hypertension of the newborn
(PPHN).
In the uterus, a baby's circulation bypasses the lungs.
Normally, when a baby is born and begins to breathe air, his or
her body quickly adapts and begins the process of respiration.
PPHN occurs when a baby's body doesn't make the normal
transition from fetal circulation to newborn circulation. This
condition can cause symptoms such as rapid breathing, rapid heart
rate, respiratory distress, and cyanosis (blue-tinged skin).
-
Transient tachypnea of the newborn (TTN)
. Rapid breathing in a full-term newborn (more than 60 breaths a
minute) is called transient tachypnea.
Although some respiratory diseases can't be prevented, many
chronic lung and respiratory illnesses can be prevented by avoiding
smoking, staying away from pollutants and irritants,
washing hands
often to avoid infection, and getting regular medical checkups.
Reviewed by:
Steven Dowshen, MD
Date reviewed: April 2007
Note: All information is for educational purposes only. For specific medical advice,
diagnoses, and treatment, consult your doctor.
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