respiratory system
Meaning of respiratory system: Conducting airways carry air without exchanging any gas, and only the final branches of the tree do the actual work of respiration.
Definition of respiratory system
The respiratory system is the group of organs that carry out breathing: the nose, throat, larynx, trachea, bronchi and lungs. Together they draw air in, deliver it to the millions of tiny air sacs deep within the lungs, and bring it within a fraction of a millimeter of the bloodstream so oxygen and carbon dioxide can trade places.
What does the upper part do?
Air entering the nose is warmed toward body temperature, moistened, and filtered by hairs and by a sticky mucus layer that traps particles. This conditioning protects the delicate tissue further down, which is part of why breathing cold dry air through the mouth for long stretches irritates the airway. The throat is a shared passage for air and food, and the larynx at its base acts as the gatekeeper, closing during swallowing so that food is directed into the esophagus rather than into the airway. The larynx also holds the vocal cords and produces voice, which is why illness in the upper airway changes the sound of speech.
How does the lower part work?
Below the larynx the trachea runs down and divides into the right and left bronchi, one for each lung. These divide again and again, around twenty times over, into ever narrower tubes ending in bronchioles no wider than a hair. Clusters of alveoli sit at the end of the smallest, thin-walled air sacs wrapped in capillaries. Everything above them is conducting airway: it moves air but exchanges no gas, which is why it is called dead space. Exchange happens only across the alveolar wall, where oxygen crosses into blood and carbon dioxide crosses out. Muscles do the pumping, as the diaphragm flattens downward and the rib muscles lift the chest, enlarging the cavity and drawing air in, while relaxation lets the elastic lung recoil and push it back out.
Why divide it into upper and lower?
| Upper respiratory system | Lower respiratory system | |
|---|---|---|
| Structures | Nose, sinuses, throat, larynx | Trachea, bronchi, bronchioles, alveoli |
| Main role | Conditioning and protecting the incoming air | Conducting air and exchanging gas |
| Typical infection | Common cold, sinusitis, laryngitis | Bronchitis, pneumonia |
| Effect on oxygen level | Generally none | It can fall, since exchange itself is affected |
The division is practical rather than decorative. Illness confined to the upper respiratory tract is usually self-limited and leaves gas exchange untouched. Illness reaching the alveoli interferes with exchange directly, which is why the same organism can cause a trivial illness in one location and a serious one further down.
Also known as
Used in a sentence
Examination of the respiratory system included listening to breath sounds in both lungs.
Good to know
Infections of the upper respiratory system, such as the common cold, are generally distinguished from infections of the lower respiratory system, such as pneumonia, since the latter more often involves the lungs directly and tends to produce more significant symptoms.
Word origin
Where “respiratory system” comes from
Formed from respiratory, from Latin respirare, meaning to breathe, combining re-, again, and spirare, to breathe.