Which one of the following is the deepest layer of the epidermis?

Question

BlackTom AI · Accepted Answer

Stratum basale is the deepest layer of the epidermis because it sits directly on the dermal–epidermal junction and contains the proliferative cells that generate the rest of the epidermal layers.

1) Relevant knowledge points and concepts
- The epidermis is organized in layers (strata) from deep to superficial: stratum basale (germinativum), stratum spinosum, stratum granulosum, (stratum lucidum in thick skin), and stratum corneum.  
- Stratum basale contains mitotically active basal keratinocytes, melanocytes, and Merkel cells; it attaches to the basement membrane via hemidesmosomes.  
- Stratum spinosum contains differentiating keratinocytes connected by desmosomes. Stratum lucidum is a thin, translucent layer found only in thick skin. Stratum corneum is composed of dead, flattened, keratin-filled cells at the surface.

2) Step-by-step reasoning
- Identify which layer is nearest the dermis: the layer directly adjacent to the basement membrane is the deepest.  
- Among the choices, only stratum basale is the basal/germinative layer. Stratum spinosum lies above the basale; stratum lucidum (when present) and stratum corneum are more superficial.

3) Calculations/intermediate steps
- (Not applicable numerically.) Conceptually, ordering from deep to superficial: basale → spinosum → granulosum → (lucidum) → corneum.

4) Why the correct answer is correct
- Stratum basale is the mitotically active, single-cell-thick layer that anchors the epidermis to the dermis; by definition it is the deepest epidermal stratum and the source of new keratinocytes that migrate outward.

5) Why other options are incorrect
- Stratum spinosum: above the basale, not deepest.  
- Stratum corneum: the outermost, most superficial layer composed of dead keratinocytes.  
- Stratum lucidum: a superficial translucent layer present only in thick skin, located between granulosum and corneum, not the deepest.

6) Conclusion
Therefore the deepest layer of the epidermis is Stratum basale, which matches the provided answer.

Which one of the following is the deepest layer of the epidermis?单项选择题

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