STRUCTURES OF THE AIRWAY
Upper Airway Anatomy
Besides being a conduit for moving air in and out, the upper airway is responsible for warming, humidifying, and purifying the air we breathe every day. It is also protected by mucus and has microscopic hair-like cilia, which undulate foreign material upward to eject it from the airway.
During inspiration, the inspired air enters through the nose or mouth, travels through the pharynx to the larynx, passes through the glottis and into the trachea.
The upper airway is made up of a surprising number of components. The actual anatomical structures are the: Nose, palate, facial bones, larynx, and cricoid cartilage. These structures create several cavities: the Nasopharynx, Oropharynx, Laryngopharynx, and Glottis.
NOSE: The nose is the only visible part of the nasal airway. However, several structures are present: the nasal cavities, nasal septum (which divides the cavities, and the paranasal sinuses.
- The nasal cavities are lined with moist mucosa that contains mucus-secreting cells, fine hairs, and the olfactory (smell) receptors. This mucosa warms and filters air as it passes though the cavity and sinuses.
NASOPHARYNX: The nasopharynx is located posterior to (behind) the nasal sinuses and leads to the oropharynx, these are separated by the palate (roof of the mouth).
FACIAL BONES: The facial bones that most impact the airway are the maxilla (making up the lower face and upper teeth) and the mandible (the lower jaw and bottom teeth).
OROPHARYNX: The oropharynx lies between the palate and the hyoid bone (located at the uppermost part of the neck). The most inferior portion of the pharynx is the laryngopharynx, through which both air and food pass. The laryngopharynx is located between the hyoid bone and the larynx and esophagus.
LARYNGOPHARYNX: The laryngopharynx is the area directly above the larynx and epiglottis. It is small compared to the oropharynx and is the last area that both food and air travel through before being divided by the epiglottis.
LARYNX: The larynx (voice box) is a cartilage and ligament-based structure that contains the vocal cords in humans. It is situated directly above the trachea and makes up the lowest part of the upper respiratory tract. It is important to know that the larynx is made up of the thyroid cartilage and the cricoid cartilage. There is also a structure known as the epiglottis that covers the top of the larynx.
Thyroid/Cricoid Cartilage: The larynx and its vocal cords are made up of and supported by cartilage. These can be felt in the anterior neck and are commonly called the "Adam's apple." The thyroid cartilage is superior (above) to the cricoid cartilage.
Epiglottis: The epiglottis is a flap of cartilage at the root of the tongue that covers the opening to the trachea during swallowing and prevents food or liquid from entering. While swallowing, the epiglottis closes off the airway and ensures food/liquid moves into the esophagus.
GLOTTIS: The glottis is a slit in the base of the trachea, ringed by the vocal cords. Speech is accomplished through air movement over the vocal cords and the expansion and contraction of the glottis.
CRICOID CARTILAGE: The cricoid cartilage is the only complete ring of cartilage that surrounds the trachea. It consists of strong connective tissue and makes up the back part of the larynx. Its purpose is to provide an anchor point for the muscles, cartilage, and ligaments involved in opening and closing the airway and producing speech.
Lower Airway Anatomy
After passing the larynx air is considered to be in the lower airway, the general path of air at this point is as follows: Trachea, Bronchi, Bronchioles, then the Alveoli. The division between upper and lower airway is significant because any foreign material in the lower airway is considered "aspirated" and has a significant risk of causing to respiratory complications.
TRACHEA: The trachea is composed of several C-shaped cartilage rings and is coated with the same mucosal and cilial cells as the nasal air passages. Mucus produced by the cells traps air contaminants to protect the lungs. The trachea divides into the right and left main stem bronchi at the carina.
BRONCHI: The bronchi are hollow tubes that are supported by cartilage rings. The air passages are first called bronchi at the carina and are considered bronchi until they become near-microscopic bronchioles.
BRONCHIOLES: The bronchioles are thin, hollow tubes that contain smooth muscle and can contract and relax. Unlike the bronchi they do not have any cartilage rings. Air flows from the bronchi to the bronchioles, where the air then reaches the end of the airway which terminates at the alveoli.
ALVEOLI: The alveoli are clusters of tiny thin-walled sacs that look like grapes on a vine. Each alveolus is surrounded by capillary blood vessels where oxygen and carbon dioxide exchange at a rapid rate.
PULMONARY CAPILLARIES: The capillaries associated with the alveoli are called "pulmonary capillaries" because their primary role is the exchange of gases with the air (pulm-).