Which of the following are functions of the epidermal layers of the skin? (Select all that apply.)
a. Provide a barrier against pathogens
b. Prevent loss of water and dehydration
c. Contain sensory receptors
d. Present foreign antigens to helper T cells
e. Prevent entry of excess water into the body
ANS: A, B, D, E
The stratum corneum is many layers of dead cells; all that remains is their keratin. An unbroken stratum corneum is an effective barrier against pathogens and most chemicals, although even microscopic breaks are sufficient to permit their entry. Keratin is relatively waterproof, so it prevents the loss of water and therefore dehydration, and also prevents the entry of excess water by way of the body surface. Also in the epidermis are Langerhans' cells, a type of macrophage that presents foreign antigens to helper T cells. This is the first step in the destruction of pathogens that have penetrated the epidermis. The sensory receptors are in the dermis.
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