What structure primarily regulates the amount of water lost through the skin?

The epidermis is primarily responsible for regulating the amount of water lost through the skin. This outermost layer of the skin is composed of several layers of cells, with the stratum corneum being the most significant when it comes to barrier function. The stratum corneum contains keratin, which is a protein that helps to create a waterproof barrier, preventing excessive loss of moisture from the body. Additionally, the epidermis contains lipids that further contribute to its barrier properties, limiting water loss while also protecting against environmental factors.

While the dermis and hypodermis play important roles in skin structure, support, and thermoregulation, they do not primarily regulate water loss. The sebaceous glands, which secrete an oily substance called sebum, help to lubricate the skin and can influence its hydration, but the main control of water loss is managed by the integrity and function of the epidermal layer.