 This video covers an introduction to the integumentary system, we will cover the following objectives, list the functions of the integumentary system, and name the tissue types that compose the epidermis, dermis, and hypodermis. The word integument comes from the Latin word for a covering, and refers to the skin, which is the cutaneous membrane composed of epidermis and dermis. The cutaneous membrane is the largest organ of the body and the primary organ of the integumentary system. The epidermis is the superficial, keratinized, stratified squamous epithelium facing the exterior of the body, and the dermis is just deep to the epidermis and is composed of connective tissue. There are two major layers of connective tissue in the dermis, a papillary layer and reticular layer. The papillary layer is composed of areolar connective tissue that is adjacent to the epidermis and provides a root for lots of small blood vessels, capillaries that provide nutrients and carry waste away from the cells and the deep layers of the epidermis. The reticular layer composed of dense irregular connective tissue provides strong structural support for the cutaneous membrane. And just deep to the dermis, the hypodermis is also known as the superficial fascia, which is a layer of adipose connective tissue. So sometimes it's known as subcutaneous adipose tissue because it's found just deep to the cutaneous membrane. And this adipose tissue provides insulation and cushioning and also a root for the large blood vessels to travel in. So large blood vessels you can see here called the cutaneous vascular plexus are traveling in through the hypodermis and sending smaller branches through the dermis. But of course there's no blood vessels that actually travel through the epidermis because the epidermis is made of epithelial tissue. There's no blood vessels within epithelial tissues. The primary function of the cutaneous membrane is to create a barrier, a protective barrier around the body. And so the cutaneous membrane contains keratin, a protein produced by cells of the epidermis that provides a physical strength to the cutaneous membrane. The superficial layers of the epidermis are composed of dead cells filled with keratin that are held tightly together, providing physical strength to prevent abrasion from damaging the epidermis. Another way the epidermis is protective is it contains a brown pigment called melanin that absorbs ultraviolet radiation to protect from the damaging effects of the sun to prevent sunburn or to reduce the risk of skin cancer that can result from ultraviolet radiation damaging DNA. The integumentary system is also important for the function of temperature regulation where there are glands in the skins that produce sweat, sweat glands produce sweat onto the surface of the skin which evaporates and cools the body down. The integumentary system also provides sensation for the sense of touch. There are a variety of extra receptors, specialized neural tissue in the cutaneous membrane found mostly in the dermis, provides the sense of touch. Another major function of the integumentary system is metabolism. There are special chemical reactions that are performed only in the cutaneous membrane. For example, the synthesis of vitamin D requires a step that occurs in the cutaneous membrane in the presence of ultraviolet light. Here we can see on the left a light microscope image of the integument with the epidermis and dermis forming the superficial cutaneous membrane and the hypodermis just deep to the cutaneous membrane composed of mostly adipose tissue with some areolar connective tissue. The hypodermis provides cushioning and insulation as well as a route for blood vessels to travel through. The dermis is composed of mostly connective tissue that supports the overlying epidermis. On the right here we can see an image zoomed in on the epidermis. There are four to five layers of the epidermis. You can see the cells in the deeper layer adjacent to the dermis. The deep layer of the epidermis contains cells that are actively dividing and as the cells mature they migrate towards the surface. These cells of the epidermis are called keratinocytes and as they mature they produce an intermediate filament protein called keratin. As the cells mature and migrate towards the surface they are moving away from the supply of nutrients in the dermis because there are blood vessels in the dermis providing a nutrient supply and no blood vessels in the epidermis. As the cells are maturing and migrating towards the surface they fill with keratin and die. The superficial layer of the epidermis facing the surface known as the stratum corneum contains keratinocytes that have died and are completely filled with keratin. This outermost layer of dead cells filled with keratin provides strength to the epidermis. You'll notice here that there are ridges in the deep layers of the epidermis. These epidermal ridges provide an increased surface area for contact between the epidermis and the dermis. The most superficial layer of the dermis projects up adjacent to the epidermal ridges in structures known as dermal papuli or papula for singular papuli for plural. Here we see a light micrograph focused on the dermis. You can see a little bit of overlying epidermis and then just deep to that epithelium is a layer of loose connective tissue of areolar connective tissue forming the papillary layer. The papillary layer gets its name from the fact that the spaces in between the epidermal ridges filled with areolar connective tissue are called dermal papuli. So the dermal papuli form the papillary layer, the most superficial layer of the dermis composed of areolar connective tissue. There's numerous small blood vessels branching through the papillary layer that provide nutrients to the overlying epidermis and carry waste away. The reticular layer of the dermis is the majority of the thickness of the cutaneous membrane. It's composed of dense irregular connective tissue and so even though it's called the reticular layer it is not composed of reticular connective tissue. It's composed of dense connective tissue where the bundles of collagen are oriented in a variety of different directions. It's composed of dense irregular connective tissue which provides strength to resist forces on the skin coming from a variety of different directions as we move our body.