Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5210_Библиотеки_им_академика_М_И_Перельмана

Non- keratinising epithelium covers the lining of mucosa. The stratum basale and spinosum are similar to the keratinised epithelium. However, the desmosomes/prickles are less conspicuous. The morphology of cells above the stratum spinosum remains relatively unchanged. The outer half of the tissue is separated into two zones: the intermediate zone (stratum intermedium) and the superficial zone (stratum superficiale). Stratum granulosum is absent, and the cells of the superfi­cial layer have plump nuclei and are stained pale pink in haematoxylin and eosin (H&E)- stained sections (Figures7.2 and7.3).

The cornified cell envelope in the keratinised epithelium involves keratins inserted in proteins and enclosed by lipids. The cells generate keratohyaline granules (Figure7.3). The granules discharge intermediate filament protein, which aggregates and causes the collapsing and flattering of keratinocytes called corneocytes. At the same time, other proteins like involucrum, trichohyaline and small proline- rich proteins are produced. Involucrin is a highly reactive, soluble, transglutami­nase substrate protein present in keratinocytes in stratified squamous epithelia(10). Trichohyaline is a structural protein expressed by keratinocytes and functions as a protective barrier.

Tight junctions are intercellular adhesion complexes in the oral epithelium limiting the epithelial permeability. These junctions block the molecules and ions passing through the intercellular spaces. They form a protein network on cellular surfaces. The essential transmembrane proteins found are claudins(13).

Gap junctions help in the diffusion of smaller molecules and ions between adjacent cells. They are crucial for electrical transduction, signalling and nutrition(14).

Desmosomes connect two adjacent cells together and are adherent points forming a continuum of cells by linking integral membrane proteins (Figure7.4). Desmosomes comprise transmembrane glycoproteins called cadherins (desmoglein and desmocollins)(15, 16).

The normal oral epithelium also contains a non- keratinising cell population. These include melanocytes, Langerhans (LCs), inflammatory and Merkel cells (MCs).

Melanocytes are present in the stratum basalis of the oral mucosa and originate from neural crest cells. They get inserted into the epithelium at 11weeks of gestation. The cells’ primary function is to produce melanin pigment, which is responsible for the colour of the mucosa along with haemo­globin and carotenoids. They are a self- reproducing population and possess dendritic processes extending amid keratinocytes(1). Histologically, they can only be identified using special stains for melanin or ‘markers’ for melanocytes (e.g. S- 100). The number of melanocytes in the oral epithe­lium is constant for all individuals. The ratio of melanocytes to keratinocytes ranges from 1:10 to 1:15(17). The diverse skin complexion and colour depend on the size and number of the melanosomes (granules containing melanin) and the form of melanin. Melanin shields the tissues from the harmful consequences of ultraviolet light, reactive oxygen species and free radicals. Physiologically, the number of oral melanocytes increases with age, leading to an amplified amount and intensity of pigmentation(18). Augmented pigmentation of the epithelium may result from inflammatory disorders, medications, recurrent minor injuries, tobacco smoke(19), hormonal disturbances and genetic abnormalities. Melanocytes release melanin into melanosomes and are then transferred by the dendritic processes to the keratinocytes’ cytoplasm. In heavy melanin pigmentation, macrophages are evident in the connective tissue that has taken up melanosomes and are labelled melanophages. Melanin pigmentation is usually seen in the gingiva, buccal mucosa, hard palate and tongue. There is a direct association between melanin pigmentation in the skin and the oral mucosa.

Normally, many inflammatory cells are seen in oral mucous membrane are short lived and not reproduced in the oral mucosa. The most common cell types are the lymphocytes, polymorphonu­clear leukocytes (PMNs) and mast cells. Scattered lymphocytes are frequently observed in the epithelium.