And this contains not only the blood vessels, the arteries and the veins, but also our excretory glands, such as our sebaceous oil gland and the sweat gland. And finally, the lower, most portion of the skin is the hypodermis, also known as the subcutaneous layer. And this layer contains not only adipose cells that insulate our body, but also macrophages cells that engulf bacterial cells. So let's begin by discussing function number one of the skin. And this is perhaps the most obvious function of the skin. So the skin creates a physical barrier that protects us from a wide range of harmful things.