Final answer:
The hypodermis, or subcutaneous layer, mainly provides insulation for the body by managing body temperature through its fat content, which keeps internal body heat from dissipating.
Step-by-step explanation:
Functions of the Subcutaneous Layer of the Skin
The subcutaneous layer, also known as the hypodermis, has several important functions within the integumentary system. One of the principal functions of the subcutaneous layer is to provide insulation for the body. This layer contains a substantial amount of fat that helps to maintain body temperature by keeping the internal body heat from dissipating into the environment. As a result, the correct answer to the question 'What is one of the principal functions of the subcutaneous layer of the skin?' would be A) It provides insulation for the body.
The hypodermis also acts as a "cushion" over underlying structures, protecting them from mechanical damage. Moreover, this layer is a significant site of long-term energy storage, as the fat within the hypodermis can be broken down into energy when needed. While the subcutaneous layer has many roles, producing oil and housing sweat glands are functions associated with other layers of the skin, and vitamin D synthesis occurs primarily in the epidermis when it is exposed to UV light.