American Academy of Professional Coders (AAPC) Practice Exam

Which of the following is NOT one of the five strata of the epidermis?

1. Stratum Corneum

2. Stratum Granulosum

3. Stratum Folliculi

4. Stratum Basale

The correct answer is: Stratum Folliculi

In the structure of the epidermis, there are indeed five recognized strata, which are important for understanding skin biology and health. The correct response identifies the stratum that is not part of the epidermal layers as "stratum folliculi." This term does not refer to a recognized layer of the skin; instead, it seems to be a conflation of terms that may refer to hair follicles rather than a distinct layer of the epidermis. The stratum corneum is the outermost layer, composed mainly of dead keratinized cells that provide a protective barrier. The stratum granulosum is situated below the stratum corneum, where cells begin to flatten and undergo keratinization, highlighting their role in forming the protective outer layer of skin. The stratum basale, also known as the stratum germinativum, is the deepest layer, containing actively dividing cells that give rise to the cells in the upper layers. In a healthy epidermis, these strata work together to protect underlying tissues, regulate moisture loss, and serve important roles in sensory perception and immune response. Thus, recognizing that "stratum folliculi" does not belong to this established anatomy reinforces the understanding of epidermal structure.