NBEO Histology Practice Test

The outermost protective layer of the skin is the stratum corneum. It is composed of keratin-filled, anucleate cells called corneocytes that have undergone cornification. These cells sit in a lipid-rich matrix and are continually shed in a process called desquamation, which maintains a robust barrier to water loss and external insults. Deeper layers include the basale (where cell division occurs), spinosum (gives strength), and granulosum (where keratinization begins with keratohyalin granules and lipid processing). In thick skin, there is also a thin stratum lucidum between granulosum and corneum, but the protective, outermost layer remains the stratum corneum.