Skin Anatomy: The Layers of Skin and Their Functions

Details About the Body's Largest Organ

woman in mirror looking at face
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The skin is the largest organ, and it's one of the most complicated. It's ever-changing, and it contains many specialized cells and structures. The skin's primary function is to serve as a protective barrier that interacts with a sometimes-hostile environment. It also helps regulate body temperature, gathers sensory information from the surrounding environment, and plays an active role in the immune system to protect the body from disease.

Learning how the skin functions begins with an understanding of the structure of the three layers of skin: the epidermis, the dermis, and subcutaneous tissue.

The Epidermis

The epidermis is the outermost layer of the three layers of skin. Its thickness depends on where it is located on the body. For example, it's thinnest on the eyelids (half a millimeter). On the palms of the hands and soles of the feet, it's thickest (1.5 millimeters).

There are five layers of the epidermis:

  • Stratum basale: This bottom layer, which is also known as the basal cell layer, has column-shaped basal cells that divide and push older cells toward the surface of the skin. As the cells move up through the skin, they flatten and eventually die and shed. 
  • Stratum spinosum: This layer, which is also known as the squamous cell layer, is the thickest layer of the epidermis. It contains newly formed keratinocytes, which are strengthening proteins. It also contains Langerhans cells that help prevent infection.
  • Stratum granulosum: This layer contains more keratinocytes moving toward the surface.
  • Stratum lucidum: This layer exists only on the palms of the hands and soles of the feet. 
  • Stratum corneum: This is the outermost or top layer of the epidermis. It's made of dead, flat keratinocytes that shed approximately every two weeks.

    The epidermis contains three specialized cells:

    • Melanocytes that produce pigment (melanin)
    • Langerhans cells that act as the first line of defense in the skin's immune system
    • Merkel cells, cells that have a function that is not yet fully understood

    The Dermis

    The dermis is the middle layer of the three layers of skin. It's located between the epidermis and the subcutaneous tissue. It contains connective tissue, blood capillaries, oil and sweat glands, nerve endings, and hair follicles. The dermis is split into two parts: the papillary dermis, which is the thin, upper layer, and the reticular dermis, which is the thick, lower layer. The thickness of the dermis varies depending on its location on the body. On the eyelids, it's 0.6 millimeters thick. On the back, the palms of hands, and the soles of feet it's 3 millimeters thick.

    The dermis is home to three different types of tissues that are present throughout:

    The dermis contains several specialized cells and structures, including:

    • Hair follicles
    • Sebaceous glands
    • Apocrine and endocrine glands
    • Blood vessels and nerve endings
    • Meissner corpuscles and Lamellar corpuscles that transmit the sensations of touch and pressure.

      The Subcutaneous Tissue

      Subcutaneous tissue is the deepest and innermost layer of the three layers of skin. It's mostly made up of fat, connective tissue and larger blood vessels and nerves.

      The thickness of this layer varies depending on where it's located on the body—for example, it's thickest on the buttocks, the soles of the feet, and the palms of the hands.

      Subcutaneous tissue is a vital component of body temperature regulation. It also acts as a cushion, so if you ever fall or hit something with your body, it protects your insides and makes the injury hurt less.

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