Skin Anatomy: Layers of the Skin and Functions

All About the Body's Largest Organ

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The skin is the largest organ, and it's also 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 to regulate body temperature, gathers sensory information from the surrounding environment and plays an active role in the immune system to protect us 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.

Epidermis

The epidermis is the outermost layer of the skin. Its thickness depends on the type of skin. For example, it's thinnest on the eyelids at half a millimeter. On the palms of the hands and soles of the feet, it's thickest at 1.5 millimeters.

There are five more layers within the epidermis:

  • Stratum basale
  • Stratum spinosum
  • Stratum granulosum
  • Stratum lucidum
  • Stratum corneum

The bottom layer, the stratum basale - 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. The stratum spinosum, 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.

The stratum granulosum contains more keratinocytes moving toward the surface and the stratum lucidum only exists on the palms of the hands and soles of the feet. The stratum corneum is the outermost layer of the epidermis. It's made of dead, flat keratinocytes that shed approximately every two weeks.

The epidermis contains three specialized cells:

Dermis

The dermis is located between the epidermis and 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 also varies depending on the location of the skin. 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 also home to three different types of tissues that are present throughout:

  • Collagen
  • Elastic tissue
  • Reticular fibers

The dermis also contains several specialized cells and structures, including:

  • Blood vessels and nerve endings
  • Meissner corpuscles and Lamellar corpuscles that transmit the sensations of touch and pressure.

Subcutaneous Tissue

Subcutaneous tissue is the deepest layer of the skin. It's mostly made up of fat, connective tissue and larger blood vessels and nerves. The thickness of this layer varies throughout the body and form person to person. Subcutaneous tissue is a vital component of body temperature regulation.

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