In which layer of the epidermis do keratinocytes begin to produce large amounts of keratin?

• A. Stratum corneum
• B. Stratum basale
• C. Stratum spinosum
• D. Stratum granulosum

Answer: (D)

Verified step by step guidance

1. Understand the structure of the epidermis, which consists of five layers: stratum basale, stratum spinosum, stratum granulosum, stratum lucidum (only in thick skin), and stratum corneum. Each layer has distinct functions and characteristics.
2. Learn the role of keratinocytes, which are the primary cells in the epidermis. These cells produce keratin, a protein that provides strength and waterproofing to the skin.
3. Focus on the stratum granulosum, the third layer of the epidermis. This is where keratinocytes begin to produce large amounts of keratin and keratohyalin, which are essential for forming the skin's protective barrier.
4. Compare the stratum granulosum to other layers: The stratum basale is where keratinocytes are formed through mitosis, the stratum spinosum is where keratinocytes start to mature, and the stratum corneum is the outermost layer composed of dead keratinized cells.
5. Conclude that the stratum granulosum is the layer where keratinocytes actively produce large amounts of keratin, making it the correct answer to the question.