How Many Layers of Skin do we Have?
There are a total of 7 layers to the skin. These layers are as follows:
- Stratum corneum
- Stratum lucidum
- Stratum granulosum
- Stratum spinosum
- Stratum basale
- Papillary Layer
- Reticular Layer
Although there are seven layers, the skin contains three major sub-divisions. The outermost division of the skin is known as the epidermis. The epidermis contains five of the seven layers of skin! The other two divisions of the skin include the dermis and the subcutis.
In the skin diagram above, notice three distinct divisions: the epidermis, dermis, and subcutis. The components and sub-components of the skin and how they function together are referred to as the integumentary system.
The epidermis is made of stratified squamous epithelial tissue and is divided into five layers. In order from outermost to innermost layer, they are as follows:
- The stratum corneum is the outermost layer and is 20-30 cells thick, made of dead keratinized cells.
- The stratum lucidum, usually only found in the palms and bottom of feet, reduces friction.
- The stratum granulosum is composed of tightly compacted, flattened cells that help waterproof the skin.
- The stratum spinosum contains irregular shaped (spiny) cells that are several cell layers thick.
- Lastly, the stratum basale layer is made up of differentiation cells that are constantly dividing to provide cells for the upper layers. Specialized cells including melanocytes and merkel cells reside in the stratum basale.
In the diagram above, notice the basement membrane. This membranous structure consists of a combination of collagen and fibers to aid in anchoring the epidermis to the dermis.
The dermis is made of dense irregular tissue and is composed of the following two layers:
- The papillary layer of the dermis lies directly below the epidermis, separated by the basement membrane. This layer of the dermis is responsible for the fingerprint, which aids in gripping objects and identification.
- The reticular layer of the dermis is deep to the papillary layer. Housing essential touch receptors, hair follicles, and glands for sweat and skin moisture, the reticular layer of the dermis serves many functions for the integumentary system.
The Subcutis is also known as the hypodermis. This structure of the skin is mostly made of fatty adipose tissue and anchors the skin to muscle tissue. This is not considered a "layer" of the skin, rather a division that is responsible for attaching skin to muscle.
Skin thickness will vary throughout the body depending on the overall function and amount of external stress imposed on the body region. For example, skin on the hands and feet is thicker than in other areas of the body. This is due to the presence of the stratum lucidum which helps reduce friction. Although skin thickness varies by location, there is a general consensus about the overall thickness of each layer of the skin.
- The epidermis ranges from 45-105 cell layers thick. This equates to between 0.2 - 1.6 millimeters thick (in heels & palms).
- The dermis is the thickest skin layer. On average, the dermis ranges anywhere from 1.5 - 4 millimeters thick.
- The subcutis layer varies in size from person to person but is generally 2.5 - 3.5 millimeters thick.
The specific cells we see as dust are keratinocytes which come from the stratum corneum layer of the epidermis. As the epidermis is exposed to the external environment, it demands many functions, including protection from pathogens and ultraviolet radiation from the sun. To accomplish this, there are specialized cells in the epidermis.
- Keratinocytes are specialized cells are the most abundantly found in the epidermis. Keratinocytes produce a protein called keratin. This protein can be described as "fibrous" and "hard," providing the skin a protective barrier to prevent water loss and resist potential physical damage. In the stratum corneum layer of the epidermis, keratinocytes are dead skin cells and regularly slough off throughout the day.
- Melanocytes are skin cells which are responsible for skin pigment, ultraviolet radiation protection, and activating the production of vitamin D. These cells extend throughout the keratinocytes, producing a pigment called melanin. The amount of melanin produced by the melanocytes is what determines characteristics of skin tone, the amount of vitamin D production, and protection from the sun's harmful ultraviolet radiation which can cause sunburn.
- Merkel Cells are specialized cells located in the stratum basale near and surrounding hair follicles. Their function is to provide sensations of lighter mechanical pressure. Without Merkel cells, fine touch and light mechanical sensations wouldn't be realized or felt.
- Langerhans Cells alert the immune system when a potential pathogen or harmful microbe lands on the skin. These cells function to detect markers on microbes that could potentially enter the body and cause harm. They function as "guard dogs" for the skin.
- Hair Follicles are anchored in the dermis, containing the site for hair cell cellular division. This site is known as the hair bulb. As cells divide, they are filled with keratin and pigments which give strength and color to the hair shaft. Small arrector pili are muscles that latch to the hair shaft. When stimulated, these pili can cause your hair to stand straight up.
- Next are touch receptors. Thermoreceptors are responsible for sensing temperature; chemoreceptors are responsible for detecting chemical imbalances; and mechanoreceptors are responsible for sensing physical touch.
- Sebaceous glands, which are housed in the dermis and attached to hair shafts, are responsible for maintaining skin lubrication and aid in killing pathogens. They do this by secreting an oily substance called sebum. These glands can become overactive during puberty and the amount of sebum produced can lead to acne or other skin irritations.
- The following are two types of sudoriferous glands (or sweat glands):
- Eccrine Glands are the most abundant sweat glands found all around the body. They are housed in the dermis and contain slender tubes that connect to the pores of the skin at the surface.
- Apocrine Glands are concentrated in the groin and armpit regions. These sudoriferous glands are responsible for excreting fats and proteins. As a result, bacteria "feed" on the excreted proteins and an unpleasant odor becomes present.
- Large Blood Vessels supply the skin with the necessary nutrients to function. They also bring waste to be excreted by the sudoriferous glands. The subcutis anchors the skin to muscle. In this way its function is similar to that of the basement membrane in the epidermis. Although the structures share a similar function, they are located in different regions of the skin.
There are three major divisions of the human skin or integumentary system. From superficial to deep (outer to inner) they are the epidermis, dermis, and subcutis. The skin is made up of 7 layers, five of which make up the epidermis (superficial to deep): 1. stratum corneum 2. stratum lucidum 3. stratum granulosum 4. stratum spinosum 5. stratum basale. Found in the dermis, the 6th and 7th layer are the papillary layer and the reticular layer. The layers of the skin are anchored to the muscles via the subcutis.
Skin thickness varies from human to human, body region to body region. Your hands and the bottom of your feet have thicker skin than your thigh or forearm. The epidermis generally ranges from 0.2mm-1.6mm thick. The dermis is on average between 1.5mm-4mm thick, and the subcutis is anywhere from 2.5mm-3.5mm thick.
The skin contains many specialized structures and cells. Some notable specialized structures in the epidermis include melanocytes which determine skin color, protect you from UV radiation, and start synthesizing the production of vitamin D. Keratinocytes which provide protection and maintain water retention. Merkel cells are able to detect light mechanical sensations. Lastly, Langerhans cells stimulate immune response when prompted.
Notable structures in the dermis include hair follicles, touch receptors, sebaceous and sudoriferous glands. Sebaceous glands secrete sebum, an oily substance, while sudoriferous glands secrete sweat, lipids, and protein.
The subcutis is a division of the skin that is concentrated with large blood vessels that bring waste to be removed and provide nutrients to the skin. The subcutis anchors the skin to muscle.
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What are the different layers of the skin?
There are seven layers to the human skin. In order from superficial to deep (external to internal) they are 1. Stratum corneum 2. Stratum lucidum 3. Stratum granulosum 4. Stratum spinosum 5. Stratum basale 6. Papillary layer 7. Reticular layer.
How thick are the layers of the skin?
Skin thickness will vary throughout the body. In the epidermis, the presence of stratum lucidum in the palms and heels will make the skin much thicker (1mm-1.6mm) than other areas of the body (0.2mm-1mm).
Although the skin thickness may vary from person to person and body region to body region, this is the average layer thickness:
epidermis = from 0.2mm - 1.6mm
dermis = from 1.5 mm - 4.5mm
subcutis = from 2.5mm - 3.5mm
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