The Respiratory System


Dr. Patel
The respiratory system, sometimes called the respiratory tract, works with the circulatory system to provide oxygen to the body's cells and to remove carbon dioxide, the waste product of cellular metabolism. All of the body's cells need oxygen to function and maintain life. Dr. Green, can you tell us more about the respiratory system?

Dr. Green
Sure, Dr. Patel. The respiratory system is divided into the upper and lower respiratory tracts. The upper respiratory tract includes:

  • The nose and mouth
  • Nasal cavities
  • Paranasal sinuses
  • The pharynx, or throat, and
  • The larynx, or voice box

The lower respiratory tract includes:

  • The trachea, or windpipe
  • The bronchi and bronchial tree, and
  • The lungs

Air enters the body through the nose and mouth when a person inhales. Structures within the nose and mouth filter the incoming air by trapping particles that would otherwise cause illness or irritation of the respiratory tract. Nasal hairs at the opening of the nostrils trap larger particles.

Smaller particles, such as pollen or smoke, are trapped by mucus secreted by a mucous membrane that lines the entire respiratory system. Hairlike structures called cilia move these particles out of the nose.

From the nose, inhaled air enters the nasal cavity. The tissue that lines the nasal cavity, called the nasal epithelium, moistens, warms, and further cleanses the inhaled air.

The nasal cavity is surrounded by the air-filled chambers called paranasal sinuses. These sinuses are named for the bones in which they are located: frontal, maxillae, ethmoid, and sphenoid.

After the nasal cavity, inhaled air passes through the pharynx, or throat. The pharynx is a muscular, funnel-shaped tube that contains the tonsils and adenoids. The tonsils and adenoids release white blood cells that fight infection.

The larynx, or voice box, forms the entrance to the lower respiratory system. Inhaled air passes through the larynx to the trachea, commonly called the windpipe. The walls of the trachea are supported by rings of C-shaped cartilage, called hyaline cartilage, that keep the trachea from collapsing.

The trachea branches off to the two primary bronchi, which lead to more bronchi that continue branching until they reach the lungs. Like the trachea, the bronchi contain hyaline cartilage rings that provide support and a mucous membrane that helps protect against foreign particles, bacteria, and viruses.

Inside the lungs, the primary bronchi branch into smaller and smaller passageways, which make up the bronchial tree. Unlike the trachea and bronchi, there is no cartilage in the smallest airways, called bronchioles.

The bronchioles end in air sacs called alveoli, which are bunched together in clusters, called alveolar sacs, that resemble bunches of grapes. Tiny blood vessels called capillaries cover the surface of the alveoli.

Here, oxygen from the alveoli and carbon dioxide from the blood are exchanged. After the blood is oxygenated, it goes to the heart, where it is pumped to the rest of the body to provide tissue cells with oxygen.

The carbon dioxide exchanged from the blood is exhaled back through the lower and upper respiratory tracts and expelled from the body through the nose or mouth.

Several muscles, including the diaphragm, intercostal muscles, and abdominal muscles, also play a role in the process of respiration.