Upper respiratory tract
Encyclopedia
The upper respiratory tract or upper airway primarily refers to the parts of the respiratory system
lying outside of the thorax
or above the sternal angle. Another definition commomly used in medicine is the airway above the glottis
or vocal cords. Some specify that the glottis
(vocal cords) is the defining line between the upper and lower respiratory tracts; yet even others make the line at the cricoid cartilage.
Upper respiratory tract infections are amongst the most common infections in the world.
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 oblongata
, the motoneurons controlling the muscles also receive tonic innervation that sets a baseline level of stiffness and size.
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
.
Respiratory system
The respiratory system is the anatomical system of an organism that introduces respiratory gases to the interior and performs gas exchange. In humans and other mammals, the anatomical features of the respiratory system include airways, lungs, and the respiratory muscles...
lying outside of the thorax
Thorax
The thorax is a division of an animal's body that lies between the head and the abdomen.-In tetrapods:...
or above the sternal angle. Another definition commomly used in medicine is the airway above the glottis
Glottis
The glottis is defined as the combination of the vocal folds and the space in between the folds .-Function:...
or vocal cords. Some specify that the glottis
Glottis
The glottis is defined as the combination of the vocal folds and the space in between the folds .-Function:...
(vocal cords) is the defining line between the upper and lower respiratory tracts; yet even others make the line at the cricoid cartilage.
Upper respiratory tract infections are amongst the most common infections in the world.
Components
- NoseHuman noseThe visible part of the human nose is the protruding part of the face that bears the nostrils. The shape of the nose is determined by the ethmoid bone and the nasal septum, which consists mostly of cartilage and which separates the nostrils...
, nasal cavityNasal cavityThe nasal cavity is a large air filled space above and behind the nose in the middle of the face.- Function :The nasal cavity conditions the air to be received by the other areas of the respiratory tract...
, and paranasal sinusParanasal sinusParanasal sinuses are a group of four paired air-filled spaces that surround the nasal cavity , above and between the eyes , and behind the ethmoids...
es - PharynxPharynxThe human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...
- NasopharynxNasopharynxThe nasopharynx is the uppermost part of the pharynx. It extends from the base of the skull to the upper surface of the soft palate; it differs from the oral and laryngeal parts of the pharynx in that its cavity always remains patent .-Lateral:On its lateral wall is the pharyngeal ostium of the...
- OropharynxOropharynxThe Oropharynx reaches from the Uvula to the level of the hyoid bone.It opens anteriorly, through the isthmus faucium, into the mouth, while in its lateral wall, between the two palatine arches, is the palatine tonsil....
- Laryngopharynx
- Nasopharynx
- LarynxLarynxThe larynx , commonly called the voice box, is an organ in the neck of amphibians, reptiles and mammals involved in breathing, sound production, and protecting the trachea against food aspiration. It manipulates pitch and volume...
(The larynx can be considered part of the upper respiratory tract, the lower respiratory tract, or both, depending on the source.)
Role in respiration
Unlike the tracheaVertebrate trachea
In tetrapod anatomy the trachea, or windpipe, is a tube that connects the pharynx or larynx to the lungs, allowing the passage of air. It is lined with pseudostratified ciliated columnar epithelium cells with goblet cells that produce mucus...
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
Thoracic diaphragm
In the anatomy of mammals, the thoracic diaphragm, or simply the diaphragm , is a sheet of internal skeletal muscle that extends across the bottom of the rib cage. The diaphragm separates the thoracic cavity from the abdominal cavity and performs an important function in respiration...
that sucks air into the lungs. This is accomplished by the rhythmic contraction of upper airway muscles, such as the genioglossus
Genioglossus
The genioglossus is a muscle of the human body which runs from the chin to the tongue. The genioglossus is the major muscle responsible for protruding the tongue.-Structure:...
(tongue) and the hyoid muscles. In addition to rhythmic innervation from the respiratory center
Respiratory center
The respiratory center is located in the medulla oblongata, which is the lowermost part of the brain stem. The RC receives controlling signals of neural, chemical and hormonal nature and controls the rate and depth of respiratory movements of the diaphragm and other respiratory muscles...
in the medulla oblongata
Medulla oblongata
The medulla oblongata is the lower half of the brainstem. In discussions of neurology and similar contexts where no ambiguity will result, it is often referred to as simply the medulla...
, the motoneurons controlling the muscles also receive tonic innervation that sets a baseline level of stiffness and size.
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:- The upper airway becomes more floppy.
- The rhythmic innervation results in weaker muscle contractionMuscle contractionMuscle fiber generates tension through the action of actin and myosin cross-bridge cycling. While under tension, the muscle may lengthen, shorten, or remain the same...
s 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
Snoring
Snoring is the vibration of respiratory structures and the resulting sound, due to obstructed air movement during breathing while sleeping. In some cases the sound may be soft, but in other cases, it can be loud and unpleasant...
, a vibration of the tissues in the upper airway. This problem is exacerbated in overweight
Overweight
Overweight is generally defined as having more body fat than is optimally healthy. Being overweight is a common condition, especially where food supplies are plentiful and lifestyles are sedentary...
people when sleeping on the back, as extra fat tissue may weigh down on the airway, closing it. This can lead to sleep apnea
Sleep apnea
Sleep apnea is a sleep disorder characterized by abnormal pauses in breathing or instances of abnormally low breathing, during sleep. Each pause in breathing, called an apnea, can last from a few seconds to minutes, and may occur 5 to 30 times or more an hour. Similarly, each abnormally low...
.
