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.
Respiratory System Basics
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
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.
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 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,
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 made by the cells as they do their
work, moves out of these cells into the capillaries, where most of it becomes 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.
Lungs & Respiratory System Problems
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:
More than 20 million people in the United States have asthma, and it's the #1 reason
that kids frequently miss school. Asthma is a chronic inflammatory lung disease that
causes airways to tighten and narrow. Often triggered by irritants such as cigarette
smoke or exposure to cold air, viral or bacterial infections of the respiratory tract,
and exposure to animal dander or pollens in kids who are allergic to them. Asthma
flares involve contraction of the muscles and swelling of the lining of 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.
Controlling asthma starts with an asthma
action plan, which usually involves avoiding asthma triggers and, sometimes, taking
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 chronic 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.
Caused by more than 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.
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
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.
This inflammation of the lungs usually happens 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
(the flu) and infection with the bacterium Streptococcus pneumoniae.
Pulmonary hypertension. This is 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 that high pressure. Pulmonary hypertension may happen in children
because of a congenital (present at birth) heart defect or
because of a health condition.
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 has trouble breathing.
(BPD). BPD 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.
Meconium aspiration is 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 is when a baby's body doesn't make that 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).
Although some respiratory diseases can't be prevented, many chronic lung and respiratory
illnesses can be prevented or made less severe by avoiding smoking, staying away from
pollutants and irritants, washing
hands often to avoid infection, and getting regular medical checkups.