The oral mucosa, which lines the inside of the mouth, is composed of various layers. In keratinized oral mucosa, specifically, there are four distinct layers that make up the epithelium. These layers are the stratum basale, stratum spinosum, stratum granulosum, and stratum corneum.
1. Stratum Basale: The stratum basale, also known as the basal layer or the germinative layer, is the deepest layer of the oral mucosa. It is made up of a single layer of cuboidal or columnar cells that are actively dividing. These cells are responsible for the constant renewal of the epithelium and the production of new cells to replace the old ones that are shed from the surface.
2. Stratum Spinosum: Above the stratum basale lies the stratum spinosum, or the prickle cell layer. This layer is characterized by the presence of numerous desmosomes, which are intercellular connections that give the cells a spiky appearance. The cells in this layer are polyhedral in shape and have larger nuclei compared to those in the stratum basale. They play a role in maintaining the structural integrity of the epithelium.
3. Stratum Granulosum: The stratum granulosum, or the granular layer, is the next layer above the stratum spinosum. It consists of flattened cells that contain granules called keratohyalin granules. These granules contain proteins that help in the process of keratinization, which is the transformation of the cells into tough, keratinized structures. The cells in this layer also undergo changes in their shape and size as they prepare to become part of the outermost layer.
4. Stratum Corneum: The stratum corneum, or the horny layer, is the outermost layer of the oral mucosa in keratinized areas. It is composed of fully keratinized, dead cells that are tightly packed together. These cells have lost their nuclei and other organelles, and they are filled with keratin, a tough protein that provides protection to the underlying layers. The stratum corneum acts as a barrier against mechanical, chemical, and microbial insults, helping to maintain the integrity of the oral mucosa.
It’s important to note that the structure and composition of the oral mucosa can vary in different areas of the mouth. While keratinized oral mucosa is found in areas such as the gingiva (gums) and hard palate, non-keratinized mucosa is present in areas like the buccal mucosa (inner lining of the cheeks) and the ventral surface of the tongue.
Understanding the different layers of the oral mucosa is essential for various reasons, such as diagnosing and treating oral diseases, evaluating the effects of certain medications or treatments on the oral mucosa, and understanding the physiological processes involved in oral health and disease.