Upper respiratory tract

Upper respiratory tract
Conducting passages.
Identifiers
FMA	45661
Anatomical terminology

The upper respiratory tract refers to the following parts of the respiratory system:

• nose and paranasal sinuses
• oral cavity (also part of the digestive system)
• throat
  • pharynx
    • genioglossus (tongue)
    • hyoid muscles
  • larynx
  • trachea

The upper respiratory tract begins with the nose and oral cavity, and ends at the branching of the trachea into two bronchi. The upper respiratory tract is part of the conducting zone.

Upper respiratory tract infections are amongst the most common infections in the world.

Role in Respiration

Unlike the trachea and bronchi, the upper airway is a collapsible, compliant tube. As such, it has to be able to withstand suction pressures generated by the rhythmic contraction of the diaphragm that sucks air into the lungs. This is accomplished by the rhythmic contraction of upper airway muscles, such as the genioglossus (tongue) and the hyoid muscles. In addition to rhythmic innervation from the respiratory center in the medulla, the motoneurons controlling the muscles also receive tonic innervation that sets a baseline level of stiffness and size.

The Upper Airway during Sleep

During non-REM sleep, the tonic drive to most respiratory muscles of the upper airway is inhibited. This has two consequences: 1. The upper airway becomes more floppy. 2. The rhythmic innervation results in weaker muscle contractions because the intracellular calcium levels are lowered, as the removal of tonic innervation hyperpolarizes motoneurons, and consequently, muscle cells.

However, because the diaphragm is largely driven by the autonomous system, it is relatively spared of non-REM inhibition. As such, the suction pressures it generates stay the same. This narrows the upper airway during sleep, increasing resistance and making airflow through the upper airway turbulent and noisy. For example, one way to determine whether a person is sleeping it to listen to their breathing - once the person falls asleep, their breathing becomes noticeably louder. Not surprisingly, the increased tendency of the upper airway to collapse during breathing in sleep can lead to snoring, a vibration of the tissues in the upper airway. This problem is exacerbated in overweight people when sleeping on the back, as extra fat tissue may weigh down on the airway, closing it. This can lead to sleep apnea.

External links

• Image at rsdrx.com