Which components make up the epidermis?

The epidermis is indeed defined as the outer protective layer of the skin. This layer serves several vital functions, including acting as a barrier against pathogens, regulating moisture loss, and providing protection from environmental factors such as UV radiation. The composition of the epidermis primarily includes keratinocytes, melanocytes, Langerhans cells, and Merkel cells, which collectively contribute to its protective role.

The other components referenced in the options pertain to different layers and structures of the skin. The underlying layer of connective tissue is part of the dermis, which supports the epidermis but is not a component of it. Blood vessels and nerve endings are also located in the dermis, providing nourishment and sensation, rather than being found in the epidermis. Muscle fibers and fat cells fall within the subcutaneous layer beneath the dermis, contributing to insulation and support but not forming part of the epidermis. Therefore, the choice identifying the epidermis as the outer protective layer of skin accurately encapsulates its primary role.