The layer beneath the epidermis that contains connective tissue and blood vessels contributing to diffusion is the:

• A. Stratum corneum
• B. Epidermis
• C. Hypodermis
• D. Dermis

Answer: (D)

Diffusion to epidermal cells comes from vessels in the layer directly beneath the epidermis. That layer, the dermis, is made of connective tissue and contains a rich network of blood vessels, providing oxygen and nutrients to the epidermis and allowing wastes to be removed. The hypodermis lies beneath the dermis and is mainly adipose tissue with its own vessels, but it is not the layer directly under the epidermis that primarily supports diffusion to epidermal cells. The outermost epidermal layer, the stratum corneum, is avascular. So the layer responsible for diffusion from blood supply into the epidermis is the dermis.