Final answer:
The question is about the selective permeability of the skin and how it allows certain substances to penetrate the dermis. It also mentions examples of both beneficial and harmful substances that can enter through the skin.
Step-by-step explanation:
The subject of this question is Biology. Specifically, it pertains to the selective permeability of the epidermis and dermis, which allows certain substances to penetrate the skin.
For example, medications like hormone replacement therapy and nicotine patches can enter the bloodstream through the capillaries in the dermis, while harmful substances like lead and pesticides can also penetrate the skin.
The permeability of the epidermis, which is the outermost layer of the skin, varies depending on several factors. The epidermis is primarily composed of layers of cells, with the outermost layer consisting of dead skin cells that are constantly sloughed off and replaced