Figure 411

The layers of the epidermis. (Adapted with permission from Montagna W and Parakkal PF. The Structure and Function of Skin [3rd ed.]. New York: Academic, 1974.)

protein keratin surrounded by hydrophobic intercellular lipids, a remarkably effective barrier to many topically applied agents. The differentiation of ker-atinocytes in the basal layer from proliferative cells to highly differentiated nondividing cells in the stratum corneum is tightly regulated by a variety of intrinsic and extrinsic factors, including cytokines and calcium. The epidermis also contains melanocytes, which synthesize the photoprotective pigment melanin, and Langerhans cells, the dendritic antigen-presenting cells that compose the farthest outpost of the body's immune system.

The dermis provides a base for the epidermis and contains fibroblasts that elaborate proteins, such as collagens and elastin, which are crucial for the skin's structural integrity. In addition, mast cells, enriched in a variety of proinflammatory substances, play an important role in tissue remodeling, wound healing, and fibrosis.

Blood Pressure Health

Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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