Dermis

Everything You Need to Know About the Dermis

Woman without any wrinkles touching her face
What is the structure and function of the dermis and why is it important in aging?. Image Source/Getty Images

What is the Dermis? - Definition

The dermis is the second and thickest layer of the three major layers of layers of skin, located between the epidermis and subcutaneous tissues, also known as the subcutis and the hypodermis.

Though we once viewed the skin as simply a form of protection from the elements, we are learning that the layers of the skin are actually very complex and have many important functions.

From goosebumps, to cooling down in the sauna, to letting your brain know your hand is on a burner, let's learn more about how this layer is structured and what it does.

Anatomy and Structure - Contents of the Dermis Layer of the Skin

The dermis has two parts: a thin, upper layer known as the papillary dermis, and a thick, lower layer known as the reticular dermis. Its thickness varies depending on the location of the skin. For example, the dermis on the eyelids is 0.6 millimeters thick; whereas on the back, the palms of hands and the soles of feet it's 3 millimeters thick.

The dermis contains a lot of the body's water supply and it has important roles in both regulating temperature and providing blood to the epidermis. Structures found in the dermis include:

  • Connective tissue - Specifically collagen and elastin
  • Blood capillaries (the smallest of blood vessels) and other small vessels
  • Lymph vessels
  • Sweat glands
  • Sebaceous glands (oil glands) - Best known for becoming plugged and causing the dreaded white heads of acne, the sebaceous glands play an important role in protecting the body
  • Nerve endings
  • Hair follicles - The body contains close to two million hair follicles

Tissue Composition of the Dermis

The dermis is composed of three types of tissues that are present throughout the dermis, not in layers:

  • Collagen
  • Elastic tissue
  • Reticular fibers

The papillary layer, the upper layer of the dermis, contains a thin arrangement of collagen fibers. The lower, reticular layer is thicker and made of thick collagen fibers that are arranged parallel to the surface of the skin.

Function - What Does the Dermis Do?

The dermis is the thickest layer of skin and arguably the most important. It plays several key roles, including:

  • Producing sweat and regulating the body's temperature. Within the dermis are sweat glands that produce sweat that comes out of the pores. The body sweats as a way to cool itself off, regulate temperature and flush out toxins. There are more than 2.5 million sweat glands on the body, and there are two different types: apocrine and eccrine. Apocrine sweat glands are found in the more odorous parts of the body, including the armpits, scalp and genital region. The sweat glands, which become active during puberty, secrete their substances into the hair follicles. The sweat that is secreted is actually odorless at first; it only starts to smell when it comes in contact with skin bacteria. Eccrine sweat glands are located throughout the rest of the body: on the palms, the soles of feet, armpits and the forehead. These glands emit their substances directly to the surface of the skin.
  • Producing oil. The sebaceous glands produce sebum, or oil. Sebum prevents bacterial growth on the skin and conditions the hair and skin. If the follicle in which sebaceous glands are located becomes clogged with excess oil or dead skin cells, a pimple develops.
  • Growing hair. Hair follicles are located in the dermis. Every follicle root is attached to tiny muscles, known as arrector pili muscles, that contract when the body becomes cold or scared, causing goosebumps.
  • Feeling. The dermis is full of nerve endings that send signals to the brain about how things feel: if something hurts, itches, or feels good.
  • Distributing blood. Blood vessels are located in the dermis, which feed the skin, remove toxins. and supply the epidermis with blood.
  • Protecting the rest of the body. The dermis contains phagocytes, which are cells that consume potentially harmful toxins and impurities, including bacteria. The dermis already protects the body, but the phagocytes provide an additional layer of protection from anything harmful that has penetrated the epidermis.
  • Giving the skin structure so it holds its shape - The dermal layer is responsible for the turgor of the skin, acting in a similar way as does the foundation of a building.

Interactions Between the Dermis and the Epidermis

Unlike the opinions of old which viewed the layers of the skin as simply a barrier to the outside the world, not only does the dermis have complex functions, but the dermis and epidermis are in constant contact and communication regulating important bodily processes.

Cells in the epidermis influence the dermis, and in turn, (via activities such as mast cells which secrete cytokines) influence the turnover of cells in the epidermis. It is the interaction of these two layers that is in fact most disrupted in some conditions such as psoriasis.

What Happens to the Dermis in Aging?

In thinking about the structure and function of the skin you may be wondering what causes the skin to age—what causes wrinkling. There are several important changes in our skin with aging in all three layers of our skin as we age.

The dermal layer becomes thinner with age and less collagen is produced. Elastin wears out—becoming less elastic just as the elastic waistband in a pair of shorts may lose its elasticity. This is what leads to wrinkling and sagging.

The sebaceous glands produce less sebum while the sweat glands produce less sweat, both contributing to the skin dryness characteristic of age.

The surface area, or amount of contact between the dermis and epidermis also decreases. This results in less blood being made available from the dermis to the epidermis and fewer nutrients making it to this outer layer of skin. This flattening out of the connecting region also makes the skin more fragile.

Tumors of the Dermis

Just as abnormal growths in the epidermis give rise to the all-too-common skin cancers, tumors can arise from the dermal layer of the skin as well. One type of tumor which begins in the dermis is called a dermatofibroma (or benign fibrous histiocytoma.) These fairly common tumors often occur on the legs of middle aged women. It's not known what exactly causes these tumors, but they frequently occur following some form of trauma.

Protecting Your Dermis

Just as it it's important to protect your epidermis from too much sun, it's important to protect your dermis as well. Sun exposure damages collagen (and causes changes in elastin) which can result in premature wrinkling.

Sources:

Kumar, Vinay, Abul K. Abbas, Jon C. Aster, and James A. Perkins. Robbins and Cotran Pathologic Basis of Disease. Philadelphia, PA: Elsevier/Saunders, 2015. Print.

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