General structural plan of the peripheral part
The external ear is the initial link of the auditory analyzer. The main physiological task of this section is to capture sound vibrations from the external environment and conduct them in a directed manner.
Structurally, this complex includes three consecutive elements:
- Auricle (pinna) — the external part protruding above the head surface.
- External acoustic meatus — the canal through which sound propagates.
- Tympanic membrane — a thin membrane acting as a structural and functional boundary between the external and middle ears.
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 similar to the typical integument of the body.
Histology of the external acoustic meatus
The external acoustic meatus is a specialized canal whose lining has a number of histological features. The surface of the canal is covered with thin skin containing hair follicles and classic sebaceous glands.
An important structural feature 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, which continues the cartilaginous base of the auricle.
The most specific feature of this region is the presence of special ceruminous glands. These are specialized tubular structures localized predominantly in the area of the upper vault of the acoustic canal. There are about 2,000 such glands in a single external acoustic meatus of an adult, and their main task is to produce the components of earwax.
Ceruminous glands and physiology of earwax
Morphologically, ceruminous glands are a modified variety of tubular sweat glands. They function via the apocrine type of secretion (where the apical part of the glandular cell is detached during secretion release).
The secretion they produce forms so-called earwax. The term originates from the Latin word cerumen, but it is important to understand that the chemical element sulfur is not present in this substance.
The biochemical composition of the secretion includes:
- Specific lipids: cholesterol itself, as well as its precursors (squalene, lanosterol).
- Fatty acids.
- Protein components: primarily protective factors of local immunity, such as immunoglobulins and the enzyme lysozyme.
- Mineral substances.
Under physiological conditions, earwax is not a pure glandular secretion, but a complex conglomerate. In addition to the output of ceruminous structures, its composition includes sebaceous gland secretions, desquamated squamous epithelial cells, and trapped dust particles from the external environment.
Functional significance of earwax:
- Protecting the delicate skin of the acoustic meatus from drying out.
- 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. Wax is removed outward independently: this process is ensured by the chewing movements of the mandible. In cases where this natural removal mechanism is impaired, a pathological accumulation of masses occurs, leading to the formation of cerumen impactions.
Briefly: answers to topical questions
Which tissue layers make up the tympanic membrane?
The tympanic membrane consists of three tissue layers: outer, middle, and inner.
- Outer layer — covered by epidermis, which is a stratified squamous keratinizing epithelium continuous with the skin of the acoustic meatus.
- Middle layer (lamina propria) — formed by two layers of dense regular connective tissue. Collagen fibers predominate, but elastic fibers are also present. In the upper part of the membrane, these fibrous layers are thinned.
- Inner layer — covered by a mucous membrane consisting of a simple squamous epithelium located on a thin layer of loose connective tissue.
To remember the type of secretion of ceruminous glands, use the association: wax in the ear APRIORI is needed for protection — the glands secrete it via the APOCRINE type.
Class and exam questions
What type of cartilage tissue forms the basis of the auricle?
The basis of the auricle is formed by elastic cartilage, which provides its flexibility and resilience.
How many ceruminous glands are located in the acoustic meatus?
There are about 2,000 tubular ceruminous glands located in the external acoustic meatus.
Is chemical sulfur present in the composition of earwax?
No, despite the name (from Latin cerumen), the chemical element sulfur is not present in it. The composition includes lipids (cholesterol, squalene, lanosterol), fatty acids, proteins, and minerals.
Why do cerumen impactions form?
Normally, earwax is removed independently thanks to the chewing movements of the mandible. When this natural elimination mechanism is impaired, excessive accumulation of the conglomerate occurs, forming an impaction.
What else to study on this topic
- Histological structure of elastic cartilage
- Structure of thin skin and its appendages (sebaceous glands and hairs)
- Mechanisms of apocrine secretion of glands
- The role of lysozyme and immunoglobulins in local immunity
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