The respiratory system includes the lungs as well as other organs that help to get oxygen into the blood and carbon dioxide out of the blood. The conducting zone of the respiratory system carries oxygen into the lungs and carbon dioxide out of the lungs. The respiratory zone is where oxygen and carbon dioxide move into and out of the blood.
Respiratory systems include lungs and other organs that help get oxygen into and carbon dioxide out of the body. Lungs are contained within the thoracic cavity, the section of the human body encased by the rib cage and separated from the abdominal cavity by the diaphragm. The thoracic cavity includes other organs such as the heart and esophagus. Human lungs are made of three lobes on the right side and two lobes on the left. The left lung contains what we call the cardiac notch, as the heart takes up this space within the thoracic cavity.
Upper and Lower Respiratory System
Parts of the upper respiratory system
Anatomically, the respiratory system can be divided into upper and lower sections. The upper respiratory system includes the mouth, nose, nasal cavity, sinuses, and the pharynx. The lower respiratory system begins with the larynx, or voice box, and includes the trachea, or wind pipe, bronchi, bronchioles, and alveoli within the lungs. It is helpful to think of the lower respiratory system as being like an upside-down tree, where the trachea is the trunk, the bronchi are the branches, and the alveoli are the leaves. Another helpful comparison for the arrangement of alveoli are clusters of grapes, where a single alveolus is like an individual grape.
Structures of the lower respiratory system
Conducting and Respiratory Zones
Now, let's discuss the respiratory system in terms of functional zones. The conducting zone, which includes everything from the nose to the smallest bronchioles, moves air into and out of the lungs. The respiratory zone includes the respiratory bronchioles and alveoli and moves the respiratory gases, that is oxygen and carbon dioxide, in and out of the blood. Note that the function of both zones is to move oxygen and carbon dioxide.
Conducting Zone: Air Movement
Let's explore the conducting zone in more detail. The conducting zone begins with the nose and nasal cavity. The trachea is part of the conducting zone, and it branches into right and left primary bronchi, carrying air to and from the right and left lung, respectively. The trachea is positioned just anterior to the esophagus and is surrounded by C-shaped tracheal cartilages. These structures provide both support and flexibility. As the structures are not closed off like a ring would be, they allow for expansion and contraction of the trachea when we breathe.
Like a tree, the conducting zone branches into smaller and smaller tubes leading to the respiratory zone, which we'll discuss here momentarily. While the conducting zone moves air in and out of the lungs, it serves other functions as well. The conducting zone cleans inspired air much like an air filter cleans air going into our furnace. Filtering is done by hair-like cellular appendages called cilia. They extend from the epithelial cells into the conducting zone.
Accumulation of filtered dirt in the conducting zone causes us to cough. Next time you hack up a loogie, take time to thank the conducting zone for working hard to keep your air clean. Furthermore, inspired air is warmed as the air passes through the conducting zone. Its temperature equilibrates with body temperature, regardless of the temperature on the outside. Finally, the conducting zone adds water vapor to the inspired air.
Respiratory Zone: Gas Exchange
Now that we've studied the conducting zone, let's take a look at the respiratory zone. The respiratory zone includes the respiratory bronchioles and the alveoli. These are microscopic structures that number in the hundreds of millions within each lung. As you can see below, small capillaries press up against the respiratory zone, bringing the blood close to the alveolar air. While the conducting zone moves air into and out of the lungs, the respiratory zone moves oxygen and carbon dioxide in and out of the blood. This process is referred to as respiration or gas exchange.
Capillaries bring blood close to alveoli
The gases exchanged, oxygen and carbon dioxide, are referred to as respiratory gases. The image below shows a single alveolus and a pulmonary capillary. As you can see, oxygen moves out of the alveolar air into the blood, and carbon dioxide moves out of the blood into the alveolar air. Now, multiply what you see by hundreds of millions, as each of our lungs contain over 100 million alveoli. Now, that's a lot of gas exchange!
Process of respiratory gas exchange
It can be helpful to think of the respiratory zone as being like a loading dock for a distribution center. Products are taken into and out of the distribution center at the loading dock. Likewise, carbon dioxide is taken into the lungs and oxygen is taken into the blood at the respiratory zone. Similarly, the capillaries can be thought of as part of a highway by which the gases are transported throughout the body.
In summary, the respiratory system includes the mouth, nose, pharynx, larynx, trachea, bronchi, bronchioles, and alveoli. The upper respiratory system begins with the nose and ends with the pharynx. The lower respiratory system begins with the larynx, or the voice box, and ends with the alveoli. Functionally, the respiratory system is divided into the conducting zone, which moves air into and out of the lungs, and the respiratory zone, which moves oxygen and carbon dioxide into and out of the blood. The process of gas exchange that occurs in the respiratory zone is referred to as respiration.
Following this video, you should be able to:
- List the structures found in the upper and lower respiratory systems
- Explain the functions of the conducting and respiratory zones