The Skin: The Dermis and Epidermis Resources and Facts

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The skin is comprised of three different layers: the dermis, the subcutaneous tissue, and the epidermis. The bottommost layer, the dermis, supplies the uppermost layer, the epidermis, with the nourishment and oxygen it needs to stay healthy. The epidermis layer of skin is the part of the skin that is visible, and is made up of four layers of keratin-producing cells.

The Four Layers of the Epidermis

Within the epidermis itself, there are four unique layers. The stratum corneum, the uppermost layer, is comprised of dead skin cells that shed. The body sheds these cells on a regular basis, but the epidermis continually replaces them. As these cells reach the surface, they begin to disintegrate, eventually falling off the top of the skin altogether. This constant regeneration takes places daily, with the average skin cell having a life span of only fourteen to twenty-eight days.

Stratum lucidum is the second layer of the skin. This layer is only present in thick skin, where it serves the purpose of reducing friction between the other layers, such as the palms of the feet or hands. The granual cell layer, also called the stratum spinosum, contains skin cells that move upward as the new cells become generated. The third layer is the stratum basala, sometimes referred to as the basal layer of skin. The basal cell layer acts as a layer of separation between the dermis and the epidermis.

How Does the Dermis Nourish the Epidermis?

There are several components that make up the epidermis as a whole, including keratin, the protein in the skin, as well as melanocytes, which carry melanin, the substance that controls the pigmentation of the skin. Because the epidermis lacks blood vessels, it cannot initiate any form of cellular regeneration on its own. Instead, the dermis is responsible for feeding nutrition to its upper-level counterpart.

Found directly below the layers of the epidermis, the dermis is a thin inner layer of living skin cells. It contains connective tissue, blood vessels, and nerve endings, but it also houses the sebaceous (oil) glands and hair follicles. Thousands of tiny papillae life upward toward the dermis, fitting into the bottom layer of the epidermis. As a source of capillaries, which supply the nourishment to the skin, the papillae are essential to allowing the new skin cells to grow.

How Does the Epidermis Renew Itself?

It’s a tough world out there. But thanks to the human skin, the body is well protected against whatever damages the environment may bring. The skin is made up of three basic layers: the lowermost layer is the hypodermis or subcutaneous tissue, used mainly for fat storage. On top of it is the dermis, from the Greek word meaning “skin”, which serves as the location for the skin’s appendages including hair, nails, and sweat glands. Finally, providing a waterproof and protective wrap over them all is the epidermis. The epidermis, from the Greek term “epi,” meaning “over” or “upon”, is the outermost layer of the skin. Because the epidermis is affected by the external world more directly, more frequently and, thus, suffers more damage, it has to constantly repair and renew itself, continually growing new cells. This ability to renew itself enables the epidermis to form a natural barrier against infection.

But before one can understand the process of renewal, one must first understand the basic architecture of the epidermis because what one sees on one’s skin is but a small part of a complex structure of cells. The epidermis is made up of a tissue called epithelium, which is composed of cells that line the cavities and surfaces of the body. The epidermis is relatively thin over most parts of the body and is much thicker on some areas like the palm of the hand and the soles of the feet.

The epidermis is made up of multiple layers of epithelial cells, including Merkel cells associated with sensing light touch, melanocytes which are partly responsible for skin color due to their production of the pigment “melanin”, and Langerhan cells which form part of the body’s immune response. However, the most important and numerous ones, which comprise 85 percent of epidermal cells, are the “keratinocytes.” So named because it produces tough proteins called “keratins” which help strengthen the skin, it is also the main cell involved in epidermal renewal or the growing of new layers of cells.

In turn, the keratinocyte is composed of several layers: the basal cells, which are attached to the basal lamina on which the keratinocyte sits, are the cells that divide; the larger prickle cells, which are located above the basal cells, serve to anchor thick tufts of keratin filaments; and, finally, the granular cells, which are sealed together to form a waterproof barrier and prevent fluid loss in the body.

Knowing the epidermal structure helps one better understand how the epidermis is continually being renewed: in the basal cells, which are the deepest layer of cells, each keratinocyte divides to form two new and identical cells. One of these stays in the basal layer in order to divide again, while the other migrates and begins the journey to the surface of the skin. As each successive layer of keratinocytes is formed, the layers of cells above them are pushed upward and outward, first through the prickle cell layer, then through the granular layer where their nucleus and intracellular organelles start to degenerate. Finally, as they come closer to the surface and reach the topmost part of the epidermis – the “stratum corneum” – the keratinocytes become flatter. These flat and dead keratinocytes, called “squamous” or “scaly” for their distinctive thin, flat shape, eventually separate from the surface by being shed or sloughed off and are replaced by new skin cells coming from below.

The time frame for the entire renewal process, from when the cell is born in the basal layer to when it is shed on the surface of the skin, is about four weeks. In the meantime, while the keratinocytes on the skin surface are dying, the granular layer continues to act as a barrier, sealing off the living cells and forming a waterproof protective “coating,” as it were, to prevent unregulated loss of water from the body.

So how often are the outermost layers of the skin replaced? In the course of one’s lifetime, probably over a thousand times, a fact that bodes well for good health and the proper functioning of the body.

Why Collagen and Elastin are Important for Healthy Skin

With the dermis, there are two essential fibers that also encourage skin nourishment: collagen and elastin. Without these fibers, the skin would not be able to stretch when the body moves or bends, nor would the skin be able to keep retract into its original shape. Collagen provides strength to the skin cells of the dermis, while elastin allows for movement.

Resources about Collagen

Information from J.M. Chen, C.E. Kung, S.H. Feairheller, E.M. Brown, J. Protein Chem., vol. 10, 535, 1991
Washington.edu’s Collagen Diagnostic Laboratory (CDL): it is housed in the Department of Pathology at the University of Washington, Seattle, WA.
MIT News article titled “Exposing collagen’s double life, Discovery that the rigid structural protein can switch to a floppy shape could lead to new treatments for heart disease.”

Sebaceous Glands and Sweat Glands

Another key component of the health of the skin are the two major glands located within the dermis, the sebaceous glands and the sweat glands. The sebaceous glands are found primarily in the face, upper back, the shoulders, and the chest. These glands secrete sebum, commonly referred to as oil, to lubricate the skin and hair. As the oil comes to the surface of the skin, the body heat melts it, allowing it to be removed within daily activities like showers, or movement. Sometimes, when the sebaceous glands are overactive, or when there is a buildup of dead skin cells in the epidermis, a blockage may occur on the surface of the skin, presenting itself as acne. On the opposite end of the spectrum, skin that does not produce enough sebum feels dry. The production of sebum is necessary to keep skin feeling soft. The other glands in the dermis, the sweat glands, serve not to nourish the skin, but instead they assist in the secretion of waste and the regulation of the temperature of the body.

Resources about The Sebaceous Gland

A normal sebaceous gland under high power.
Cct.edu’s image of a Sebaceous gland, arrector pili muscle

The epidermis is completely dependent upon all of the functions of the dermis for its continued supply of nutrients. The dermis not only helps keep the skin functioning in its regenerative state, but it also helps regulate the ongoing healing and repair of the skin.

Resources about The Skin

Information about the skin from umm.edu.
Pictures of the different lawyers of the skin.
Hey Your epidermis is showing! What is the epidermis, anyway?
list of skin disorders from uiowa.edu.

Resource by Thrive Med Spa

Thrive Med Spa is a leading medical spa in Chicago that is privately owned and operated by Dr. Barry Summers, a Board Certified General & Cosmetic Surgeon. Thrive Medical Spa, has two convenient downtown locations in Lakeview and the Gold Coast. Thrive is the leading medical spa and rejuvenation center in Chicago ( and Thrive Laser Training School) and is dedicated to providing clients with the highest quality of care and state of the art treatments for cosmetic and skin rejuvenation .

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