stratum basale
Summary
The stratum basale is the deepest layer of the epidermis, where stem-like keratinocytes divide by mitosis to replace cells shed from the surface. It also contains melanocytes and Merkel cells. The testable point: it is the epidermal layer of cell division.
Detail
Meaning: The stratum basale is the deepest layer of the epidermis, resting on the basement membrane just above the dermis. Its basal keratinocytes divide by mitosis, hence the alternate name stratum germinativum. Daughter cells move upward through the stratum spinosum, granulosum, and corneum (plus lucidum in thick skin), making keratin and dying before they are shed. The layer also holds melanocytes, which pass melanin to neighboring keratinocytes to shield their DNA from UV light, and Merkel cells, which function in light touch.
On the MCAT: Expect questions asking which epidermal layer is the site of cell division or contains melanocytes, or asking for the order of layers from deep to superficial. The epidermis has no blood vessels, so basal cells get oxygen and nutrients by diffusion from dermal capillaries, and cells pushed farther from that supply die as they mature. A passage on UV exposure or skin turnover usually points back to this layer.
Common confusion: Darker skin is not mainly due to more melanocytes. Melanocyte numbers are broadly similar among people; the difference lies in the amount, type, and distribution of the melanin they make. Also, the stratum basale belongs to the epidermis, not the dermis, which lies below the basement membrane.
Sources
- Campbell Biology
- Human Anatomy & Physiology (Marieb)
- Principles of Anatomy and Physiology (Tortora)
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.