The Eustachi tube is the medical term for the eustachian tube that connects the nasopharynx to the middle ear. This anatomical structure serves to equalize pressure and drain secretions. Both constant occlusion and lack of occlusion of the eustachian tube possess disease value.
What is the Eustachian tube?
The Eustachi tube is also known as the eustachian tube or tuba auditiva. The tympanic cavity of the middle ear is connected to the nasopharynx by this tube, which is about 30 to 35 millimeters long. The tube extends through the posterior floor of the bony petrous bone canal and is composed of two distinct sections. Birds, as well as reptiles and mammals, are equipped with the paired tube connection. Some animals in the unpaired ungulate genus also have a saccular extension of the tubular junction, also known as an air sac. The Italian anatomist Bartolomeo Eustachi gave the Eustachi tube its name. He first accurately described the tube-like connection between the middle ear and the nasopharynx during the 16th century. Alkmaion is said to have discovered the structure as early as 500 BC. However, the description at that time wrongly assumed an additional breathing opening in it, with which, according to the knowledge at that time, only goats seemed to be equipped. Only Eustachi documented the tube in its actual shape and function. During embryonic development, the auditory tube arises from the proximal recessus tubotympanicus, which corresponds to a bulge of the first pharyngeal pouch.
Anatomy and structure
Toward the tympanic cavity lies the bony part of the auditory tube. The cartilaginous part of the structure is located toward the nasopharynx and accounts for approximately two-thirds of the total eustachian tube. The cartilaginous structure corresponds to an elastic cartilage, which is also called tubal cartilage. This tubal cartilage consists of a thin end and a wide end and is attached to three muscles. These three muscles are the pharyngeal muscles Musculus tensor veli palatini, Musculus levator veli palatini and Musculus salpingopharyngeus. The tensor veli palatini muscle is located at the thin end of the cartilage and tenses against the inherent tension of the tubal cartilage. The levator veli palatini muscle is located at the lower end of the tubal cartilage and pushes this part of the tube upward. The salpingopharyngeus muscle is located centrally at the thick end of the cartilage and keeps the movements under control by the levator veli palatini muscle. In a physiological constriction, the cartilaginous and bony sections of the auditory tube merge. The tube can open both toward the nasopharynx and toward the tympanic cavity. The opening toward the nasopharynx also includes two mucosal protrusions.
Function and tasks
As long as the auditory tube is closed, it protects the middle ear from ascending infections from the nasopharynx. This closure function is performed by the tubal cartilage, which compresses the tube by its own tension. The three muscles Musculus tensor veli palatini, Musculus levator veli palatini and Musculus salpingopharyngeus control tube closure. Only when swallowing, yawning and articulating certain sounds does the Eustachi tube open. This opening is sometimes noticeable as a clicking sound in the ear. Air pressure equalization takes place in the Eustachian tube during opening. The pressure in the middle ear can thus be adjusted to the air pressure in the nasopharynx and thus to the air pressure outside. This equalization takes place primarily during swallowing and yawning. However, if you hold your nose and mouth shut and try to exhale at the same time, you can also arbitrarily cause the eustachian tube to open and thus specifically initiate pressure equalization. This process is also known as the Valsalva maneuver. Similarly, selective tension of the three pharyngeal muscles can open the tuba auditiva, allowing pressure equalization to occur. Without air pressure equalization, the eardrum would bulge painfully. In addition to its pressure-balancing functions, the eustachian tube also serves as a middle ear drainage system. Fluid is drained from the middle ear via the auditory tube.
Diseases
In diseases involving the upper respiratory tract, the Eustachi tube may become narrowed due to swelling of the mucous membranes. Obstruction of the tube may cause, for example, a tympanic effusion, a painful accumulation of fluid in the middle ear.Complete occlusion of the auditory tube is also known as tubal middle ear catarrh. In some circumstances, bacterial infections ascend into the middle ear through the auditory tube in respiratory tract infectious diseases, triggering middle ear infections. Most middle ear infections are bacterial in nature. Less commonly, fungi or viruses are responsible for the infection. Sometimes the eustachian tube develops into a gaping tube. In this phenomenon, the eustachian tube remains largely open. The physician then speaks of a lack of tube closure. A leading symptom of this phenomenon is the so-called autophony. Own body sounds are henceforth perceived as unnaturally loud, because they are transmitted directly into the middle ear. Various causes are possible for this phenomenon. Hormonal changes and severe weight loss are among them, as are scars in the nasopharynx or possible tumor irradiation. In both gaping tuba and tubal middle ear catarrh, the eardrum remains intact in most cases, contrary to popular belief. The ear specialist can check the permeability of the tuba autitiva in the course of the so-called tubal function test. This functional test may correspond to a blow-through, but it may also include the Valsava test.
