Structure of the organ wall

Larynx and the concept of layer reduction

In the classical model, the wall of a hollow organ consists of several standard layers. However, the histological picture of the larynx demonstrates an important exception to this rule. By analogy with the structure of the nasal cavity, the submucosa is completely absent in the wall of the larynx.

The architectonics of the larynx are represented by only three membranes:

1. Mucosa (mucous membrane).
2. Fibro-musculo-cartilaginous membrane — its thickness, as well as its specific histological composition, vary significantly depending on the section of the larynx being examined.
3. Adventitial membrane.

Embryonic features: oral cavity

Organs developing from the endoderm and prechordal plate have their own specific features. The oral cavity is the initial section of the digestive tube, but its walls differ drastically from the typical structure of the underlying sections.

Main histological differences of the oral cavity:

• The mucous membrane completely lacks a muscular lamina (lamina muscularis mucosae).
• The outer membrane is not expressed: there is neither an adventitial nor a serous membrane here.

The structure of the mucous membrane directly depends on whether it covers soft or hard tissues:

• Soft walls: lined with non-keratinized stratified squamous epithelium, which is a derivative of the prechordal plate. Beneath it lies the lamina propria of the mucosa (lamina propria). It is formed by loose fibrous connective tissue and forms characteristic papillae that deeply penetrate the epithelial layer.
• Hard walls (palate, gums): demonstrate an even more specific structure. In these zones, the submucosa is usually absent. Because of this, the mucous membrane is tightly fused directly with the periosteum (periosteum).

Esophagus: anatomy and relief

The esophagus has a number of important anatomical features. Three physiological constrictions are distinguished along its length:

• At the level of the cricoid cartilage.
• At the site of contact with the aorta.
• In the area of passage through the diaphragm.

The relief of the inner surface of the organ is formed by 7–10 pronounced longitudinal folds. Two layers participate in the formation of these folds at once: the mucous membrane and the submucosa. During the passage of a food bolus, these longitudinal folds straighten out. Such a mechanism ensures the necessary expansion of the esophageal lumen.

Clinical histology: assessment of invasion depth (P)

Knowledge of organ wall layers is of critical importance in oncological practice. To assess the degree of spread of a malignant process, a special histological criterion is used — the depth of invasion, or penetration (from English Penetration — P). This indicator reflects how deeply the cancer has grown into the wall of a hollow organ.

Four degrees of invasion are distinguished:

• P1: Cancer infiltrates only the mucosa.
• P2: The tumor process spreads deeper, infiltrating the submucosa.
• P3: Cancer continues to grow and reaches the subserosal layer.
• P4: The most severe degree, in which the tumor infiltrates the serosa or completely extends beyond the wall of the affected organ.

This criterion is an integral part of the general tumor classification formula, which looks as follows: T(1-4) N(0-3) M(0-1) G(1-3) P(1-4).

Class and exam questions

What else to study on this topic

• Histological composition of the fibro-musculo-cartilaginous membrane in different parts of the larynx.
• Embryonic development of organs from the prechordal plate and endoderm.
• Morphology of the lamina propria of the mucous membrane and its papillae.
• Anatomical features of the physiological constrictions of the esophagus.
• Complete decoding of the components of the T-N-M-G-P oncological formula.

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