Anatomy and Physiology of the Respiratory System
Body cells require an abundant and continuous supply of oxygen. As the cells use oxygen, they release carbon dioxide, a waste product that the body must get rid of. The respiratory system works together with the cardiovascular system to deliver oxygen to all the cells of the body. The respiratory system is composed of six major organs—the nose, pharynx, larynx, trachea, bronchial tubes, and lungs—that
function together to perform the mechanical and, for the most part, unconscious mechanism of respiration.
The respiratory system consists of a group of passages that filter incoming air and
transport it into the body, into the lungs and to the many microscopic air sacs where gases are exchanged. The entire process of exchanging gases between the atmosphere and body cells is called respiration. It involves at least four events: Pulmonary ventilation: The tidelike movement of air into and out of the lungs so that the gases in the alveoli are continuously changed and refreshed. Also more simply called ventilation, or breathing.
External respiration: The gas exchange between the blood and air-filled chambers of the lungs(oxygen loading/ carbon dioxide unloading).the gases diffuse in opposite directions between the air sacs of the lungs and the bloodstream. Oxygen enters the
bloodstream from the air sacs to be delivered throughout the body. Carbon dioxide
leaves the blood stream and enters the air sacs to be expelled form the body during exhalation.
Transport of respiratory gases: The transport of respiratory gases between the lungs
and tissue cells of the body accomplished by the cardiovascular system, using blood as the transport vehicle.
Internal respiration: Exchange of oxygen and carbon dioxide at the cellular level. At this time oxygen leaves the bloodstream and is delivered to the tissues. Oxygen is necessary for the body cells’ metabolism, all the physical and chemical changes
within the body that are necessary for life. The by-product of metabolism is the
formation of a waste product, carbon dioxide. The carbon dioxide enters the bloodstream from the tissues and is transported back to the lungs for disposal. Internal respiration is sometimes referred to as tissue breathing since the cells within the
body also must breathe fresh oxygen or, in other words, have a fresh supply of oxygen to maintain life.
Air generally passes into the respiratory tract through the external nares (nostrils), and enters the nasal cavity (divided by the nasal septum). It then flows posteriorly
over three pairs of lobelike structures, the inferior, superior, and middle nasal conchae,
which increase the air turbulence. As the air passes through the nasal cavity, it is warmed, moistened, and filtered by the nasal mucosa. The nasal cavity is surrounded
by the paranasal sinuses in the frontal, sphenoid, ethmoid, and maxillary bones.
These sinuses act as resonance chambers in speech and their mucosae, like that of the nasal cavity, warm and moisten the incoming air.
The nasal passages are separated from the oral cavity below by a partition composed anteriorly of the hard palate and posteriorly by the soft palate.
After passing through the nasal cavity, the air next reaches the pharynx (throat). There are three division of the pharynx: the nasopharynx, the oropharynx, and the
laryngopharynx. The nasopharynx is the first division, and it is nearest to the nasal cavities. It contains the adenoids (also known as the pharyngeal tonsils), which are
collections of lymphatic tissue. Below the nasopharynx and closer to the mouth is the second division of the pharynx, the oropharynx. In its lateral walls are the palatine
tonsils, two rounded masses of lymphatic tissue. The lingual tonsil covers the base of
the tongue. The third division of the pharynx is the laryngopharynx. It lies directly
posterior to the upright epiglottis and extends to the larynx, where the common
pathway divides into the respiratory and digestive channels. From the laryngopharynx, air enters the lower respiratory passageways by passing through the larynx (voice box) and into the trachea below. Pharynx serves as a food and air passageway. Air enters from the nasal cavities and passes through the pharynx to the larynx. Food enters the pharynx from the mouth and passes into the esophagus.
The larynx is the location of the vocal cords. It consists of nine cartilages. The two
most prominent are the large shield-shaped thyroid cartilage, whose anterior medial
laryngeal prominence is commonly referred to as Adam’s apple, and the inferiorly
located, ring-shaped cricoid cartilage, whose wildest dimension faces posteriorly. A
flap of cartilaginous tissue, the epiglottis, sits above the glottis. The epiglottis
provides protection against food and liquid being inhaled into the lungs since it covers the larynx and trachea during swallowing.
On its way to the lungs, air passes from the larynx to the trachea (windpipe), a vertical tube approximately 12.5 centimeters in length and 2.5 centimeters in diameter.
It extends downward in front of the esophagus and into the thoracic cavity, where it splits into right and left bronchi. Within the tracheal wall are about twenty C-shaped
pieces of hyaline cartilage, one above the other. The open ends of these incomplete
rings are directed posteriorly, and the gaps between their ends are filled with smooth muscle and connective tissues. The inner wall of the trachea is lined with a ciliated mucous membrane that contains many goblet cells. This membrane continues to filter the incoming air and to move entrapped particles upward into the pharynx where the mucus can be swallowed.
The distal end of the trachea divides to form the left and right main bronchi. Each bronchus enters one of the lungs and branches repeatedly to form secondary bronchi. Each branch becomes more narrow until the most narrow branches, the bronchioles,
are formed. Each bronchiole terminates in a small group of air sacs, called alveoli.
Each lung has approximately 150 million alveoli. A network of pulmonary
capillaries from the pulmonary blood vessels tightly encases each alveolus. In fact, the walls of the alveoli and capillaries are so tightly associated with each other they are referred to as a single unit, the respiratory membrane. External respiration, the
exchange of oxygen and carbon dioxide between the air within the alveolus and the blood inside the capillaries, takes place across the respiratory membrane.
The lungs are soft, spongy, cone-shaped organs located in the thoracic cavity. The right and left lungs are separated medially by the mediastinum, and they are enclosed
by the diaphragm and the thoracic cage.
Each lung is enveloped in a double-folded membrane called the pleura. The outer
layer of the pleura, nearest the ribs, is the parietal pleura, and the inner layer, closest
to the lung, is the visceral pleura. The pleura is moistened with a serous fluid that
facilitates the movements of the lungs within the chest.
The right lung is slightly larger than the left one. It is divided into three lobes and the left lung is divided into two lobes. The uppermost part of the lung is called the apex, and the lower area is the base. The hilum of the lung is the midline region
where blood vessels, nerves, lymphatic tissue, and bronchial tubes enter and exit the organ. The area between the right and left lung is called the mediastinum. The mediastinum contains the heart, esophagus, thymus gland, and main bronchi.
Mechanics of Respiration
The lungs extend from the clavicle to the diaphragm in the thoracic cavity. The
diaphragm is a muscular partition that separates the thoracic from the abdominal cavity and aids in the process of breathing. The diaphragm contracts and moves down into the abdominal cavity, which causes a decrease of pressure, or negative thoracic pressure, within the chest cavity. Air can then enter the lungs to equalize the pressure during inhalation. The intercostal muscles between the ribs assist inhalation by
raising the rib cage to enlarge the thoracic cavity.
The diaphragm and intercostal muscles relax and the thoracic cavity becomes smaller, when pressure within the cavity increases and air is pushed out of the lungs, resulting in exhalation. Therefore, a quiet, unforced exhalation is a passive process since it does not require any muscle contraction.
Respiratory Volumes and Capacities
A person’s size, sex, age, and physical condition produce variations in respiratory volumes. Normal quiet breathing moves about 500 ml of air in and out of the lungs with each breath. On the average, the same amount leaves during a normal resting expiration. One inspiration plus the following expiration is called a respiratory cycle. Terminology relating to this measurement is listed below.
Tidal volume (TV): the amount of air that enters the lungs in a single inhalation or leaves the lungs in a single exhalation of quiet breathing. In an adult this is normally
Inspiratory reserve volume (IRV): the air that can be forcibly inhaled after a normal respiration has taken place. Also called complemental air, generally measures around 3,000 cc.
Expiratory reserve volume (ERV): the amount of air that can be forcibly exhaled
after a normal quiet respiration. This is also called supplemental air, approximately 1,000 cc.
Residual volume: the air remaining in the lungs after a forced exhalation; about 1,500 cc in the adult.
Inspiratory capacity (IC): the volume of air inhaled after a normal exhale.
Functional residual capacity (FRC): the air that remains in the lungs after a normal
exhalation has taken place.
Vital capacity (VC): the total volume of air that can be exhaled after a maximum inhalation. This amount will be equal to the sum of TV, IRV, and ERV. Total lung capacity (TLC): the volume of air in the lungs after a maximal inhalation. Respiratory Rate
The respiratory rate is one of our vital signs (VS), along with heart rate,
temperature, and blood pressure. Respiratory rate is dependent on the level of CO2 in the blood. When the CO2 level is high, we breathe more rapidly to expel the excess. However, if CO2 levels drop, our respiratory rate will also drop.
When a respiratory rate falls outside the range of normal, it would indicate an illness or medical condition. For example, when a patient is running an elevated temperature and has shortness of breath (SOB) due to pneumonia, the respiratory rate may increase dramatically. However, some medications, pain medication in particular, can cause a decrease in the respiratory rate.
Respiratory Rates for Different Age Groups
Age Respirations per Minute
Combining Forms Commonly Used in This System Combining form Meaning Example
adenoid/o adenoids adenoidectomy
alveol/o alveolus; air sac alveolar
bronch/o bronchus bronchoscope
bronchi/o bronchus bronchiectasis
bronchiol/o bronchiole, small bronchiolitis
capn/o carbon dioxide acapnia
epiglott/o epiglottis epiglottitis laryng/o larynx, voice box laryngospasm
lob/o lobe lobectomy
muc/o mucus mucus nas/o nose nasopharynx ox/o oxygen anoxia pharyng/o pharynx pharyngeal tonsils pleur/o pleura pleurocentesis pneum/o air, lung pneumothorax pneumon/o
pulmon/o lung pulmonology rhin/o nose rhinorrhagia sinus/o sinus, cavity pansinusitis spir/o breathing spirometer tonsill/o tonsils tonsillectomy trache/o trachea, windpipe tracheotomy thorac/o chest thoracalgia Suffixes Commonly Used in This System Suffixes Meaning Example -capnia carbon dioxide hypercapnia -ectasis stretching out, dilatation, bronchiectasis
-emia blood condition hypoxemia -oxia oxygen anoxia -pnea breathing dyspnea Diagnostic Procedures Relating to This System chest X-ray taking a radiographic picture of the lungs and
heart from the back and sides.
chest CT(computed computerized images of the chest reproduced in
tomography) scan from front to back horizontally. Used to diagnose
tumors, abscesses, and pleural effusion. Computed
tomography is used to visualize other body parts
such as the abdomen and the brain.
pulmonary function tests(PFT) a group of diagnostic tests that give information
regarding air flow in and out of the lungs, lung
volumes, and gas exchange between the lungs and
tuberculin skin tests(TB test) applying a chemical agent (Tine or Mantourx tests)
under the surface of the skin to determine if the
patient has been exposed to tuberculosis. ventilation-perfusion scanning(VPS) a nuclear medicine procedure used to diagnose
pulmonary embolism and other condition.
Radioactive air is inhaled for the ventilation
portion to determine if air is filling the entire
lung. Radioactive intravenous injection shows
whether or not blood is flowing to all parts of
Bronchiectasis: Bronchiectasis is destruction and widening of the large airways. A person may be born with it (congenital bronchiectasis) or may develop it later in life.
Bronchiectasis is often caused by recurrent inflammation or infection of the airways. It may be present at birth, but most often begins in childhood as a complication from infection or inhaling a foreign object.
Cystic fibrosis causes about 50% of all bronchiectasis in the United States today. Recurrent, severe lung infections (pneumonia, tuberculosis, fungal infections), abnormal lung defenses, and obstruction of the airway by a foreign body or tumor are some of the predisposing factors. It can also be caused by routinely breathing in food particles while eating.
Symptoms often develop gradually, and may occur months or years after the event that causes the bronchiectasis.
? Chronic cough with large amounts of foul-smelling sputum production
? Coughing up blood
? Cough worsened by lying on one side
? Shortness of breath worsened by exercise
? Weight loss
? Clubbing of fingers may be present (abnormal amount of tissue in the
? Skin discoloration, bluish
? Breath odor
When listening to the chest with a stethoscope, the doctor may hear small clicking, bubbling, wheezing, rattling, or other sounds, usually in the lower lobes of the lungs. Tests may include:
? Chest x-ray
? Chest CT
? Sputum culture
? Sweat test or other cystic fibrosis testing
? Serum Immunoglobulin analysis
? Serum precipitins (testing for antibodies to the fungus aspergillus)
? PPD (purified protein derivative) skin test for prior TB infection
Treatment is aimed at controlling infections and bronchial secretions, relieving airway obstruction, and preventing complications.
Antibiotics, bronchodilators, and expectorants are often prescribed for infections. Regular, daily drainage to remove bronchial secretions is a routine part of treatment. A respiratory therapist can teach postural drainage and effective coughing exercises to patients and their families.
Surgical lung resection may be indicated for those who fail to respond to therapy or for massive bleeding.
Childhood vaccinations and a yearly influenza vaccine help reduce the chance of some infections. Avoiding upper respiratory infections, smoking, and pollution
may lessen the susceptibility to infection.
Pneumonia: Pneumonia is an infection of the lungs. Many different organisms can cause it, including bacteria and viruses.
Pneumonia can range from mild to severe, and can even be deadly. The severity depends on the type of organism causing pneumonia, as well as your age and underlying health.
Bacterial pneumonia tends to be the most serious and, in adults, the most common cause of pneumonia. The most common pneumonia-causing bacterium in adults is Streptococcus pneumoniae (pneumococcus). In some people, particularly the
elderly and those who are debilitated, bacterial pneumonia may follow influenza or
even a common cold.
Respiratory viruses are the most common causes of pneumonia in young children, peaking between the ages of 2 and 3. By school age, the bacterium Mycoplasma
pneumoniae becomes more common.
People who have trouble swallowing are at risk of aspiration pneumonia. In this condition, food, liquid, or saliva accidentally goes into the airways. It is more common in people who have had a stroke, Parkinson's disease, or previous throat surgery.
It is often harder to treat pneumonia in people who are in a hospital, or a nursing facility.
The main symptoms of pneumonia are:
? Cough with greenish or yellow mucus; bloody sputum happens on occasion
? Fever with shaking chills
? Sharp or stabbing chest pain worsened by deep breathing or coughing
? Rapid, shallow breathing
? Shortness of breath
Additional symptoms include:
? Excessive sweating and clammy skin
? Loss of appetite
? Excessive fatigue
? Confusion, especially in older people
If you have pneumonia, you may be working hard to breathe, or may be breathing fast. Crackles are heard when listening to your chest with a stethoscope. Other abnormal breathing sounds may also be heard through the stethoscope or via percussion (tapping on your chest wall).The health care provider will likely order a chest x-ray if pneumonia is suspected.
Some patients may need other tests, including:
? Gram's stain and culture of your sputum to look for the organism causing your
? CBC to check white blood cell count; if high, this suggests bacterial infection
? Arterial blood gases to check how well you are oxygenating your blood
? CAT scan of the chest
? Pleural fluid culture if there is fluid in the space surrounding the lungs If the cause is bacterial, the doctor will try to cure the infection with antibiotics. If the cause is viral, typical antibiotics will NOT be effective. Sometimes, however, your doctor may use antiviral medication. It may be difficult to distinguish between viral and bacterial pneumonia, so you may receive antibiotics.
Many people can be treated at home with antibiotics. You can take these steps at home:
? Drink plenty of fluids to help loosen secretions and bring up phlegm.
? Get lots of rest. Have someone else do household chores.
? Control your fever with aspirin or acetaminophen. DO NOT give aspirin to
If you have an underlying chronic disease, severe symptoms, or low oxygen levels, you will likely require hospitalization for intravenous antibiotics and oxygen therapy. Infants and the elderly are more commonly admitted for treatment of pneumonia. When in the hospital, respiratory treatments to remove secretions may be necessary. Occasionally, steroid medications may be used to reduce wheezing if there is an underlying lung disease.
Emphysema: Emphysema is a condition in which the walls between the alveoli or air sacs within the lung lose their ability to stretch and recoil. The air sacs become weakened and break. Elasticity of the lung tissue is lost, causing air to be trapped in the air sacs and impairing the exchange of oxygen and carbon dioxide. Also, the support of the airways is lost, allowing for airflow obstruction.
Symptoms of emphysema include shortness of breath, cough and a limited exercise tolerance. Emphysema and chronic bronchitis frequently co-exist together to comprise chronic obstructive pulmonary disease (COPD). COPD does not include other obstructive lung diseases such as asthma.
Cigarette smoking is by far the most common cause of emphysema. Smoking is responsible for approximately 80-90% of deaths due to COPD.1
In addition, in the absence of alpha 1-antitrypsin (AAT), an inherited form of emphysema called alpha 1-antitrypsin deficiency related emphysema is almost inevitable. Symptoms of AAT deficiency emphysema usually begin between 32 and