General Organization of the Peripheral Auditory System
The external ear represents the initial link in the auditory pathway. The primary physiological objective of this section is to capture sound vibrations from the external environment and conduct them in a targeted manner.
Structurally, this complex includes three consecutive elements:
- Auricle (Pinna) — the outer part projecting above the surface of the head.
- External acoustic meatus — the canal through which sound propagates.
- Tympanic membrane (Eardrum) — a thin membrane acting as a structural and functional boundary between the external and middle ear.
The histological organization of the auricle is relatively simple. Its internal supporting framework is formed by elastic cartilage, which gives the structure the necessary elasticity and the ability to maintain a complex geometric shape. Externally, the cartilaginous base is completely covered by skin, the structure of which is analogous to typical skin covering the body.
Histology of the External Acoustic Meatus
The external acoustic meatus is a specialized canal whose lining has several histological features. The surface of the meatus is covered by thin skin containing hair follicles and classic sebaceous glands.
An important structural characteristic is the presence of a supporting component: in the outer third (the first third) of the acoustic canal, directly beneath the skin, lies elastic cartilage continuing the cartilaginous framework of the auricle.
The most specific feature of this region is the presence of specialized ceruminous glands. These are specialized tubular structures located predominantly in the region of the upper vault of the acoustic canal. In a single external acoustic meatus of an adult, there are about 2,000 such glands, whose main task is to produce the components of earwax.
Ceruminous Glands and the Physiology of Cerumen
Morphologically, ceruminous glands are a modified variety of tubular sweat glands. They function via an apocrine secretion mechanism (where the apical part of the glandular cell is pinched off during secretion release).
The secretion they produce forms earwax (cerumen). Although derived from the Latin word cerumen, it is important to understand that the chemical element sulfur (Latin: sulphur) is not present in this substance.
The biochemical composition of the secretion includes:
- Specific lipids: cholesterol directly, as well as its precursors (squalene, lanosterol).
- Fatty acids.
- Protein components: primarily local immune defense factors such as immunoglobulins and the enzyme lysozyme.
- Mineral substances.
Under physiological conditions, earwax is not merely pure glandular secretion, but a complex conglomerate. In addition to ceruminous output, it incorporates sebum from sebaceous glands, desquamated stratified squamous epithelial cells, and trapped dust particles from the external environment.
Functional significance of earwax:
- Protecting the delicate skin of the acoustic meatus from desiccation.
- Ensuring the self-cleaning of the canal from foreign dust particles and bacterial agents.
Mechanism of physiological clearance: Normally, the accumulated conglomerate does not require mechanical extraction. Earwax is cleared outward independently: this process is facilitated by the masticatory movements of the mandible. When this natural removal mechanism is impaired, pathological accumulation of masses occurs, leading to the formation of cerumen impaction.