Structure of skin

The skin is composed of three layers: epidermis, dermis, and subcutaneous fat layer.

a image of skin structure layer

Now let's look at the epidermis, dermis, and subcutaneous tissue layers one by one.

Subcutaneous layer

an image of epidermis layer of skin

It is the innermost part of the skin. The subcutaneous tissue is mainly composed of fat cells. Subcutaneous fat refers to fat cells in the subcutaneous tissue.

The role of the subcutaneous tissue layer is to:

1. body temperature control

2. protect the body from impact

1. Body temperature control

The layer of subcutaneous tissue regulates heat loss from the body by storing high-calorie nutrients. In other words, it plays a role in regulating body temperature.

2. Protect the body from impact

In addition, subcutaneous fat acts as a kind of cushion to protect the body from external shocks.

Dermis layer

an image of epidermis layer of skin

The dermis accounts for about 90% of the skin and is said to be 10 to 40 times thicker than the epidermis. The dermis is composed of collagen and elastic fibers (elastin). In other words, it can be said that it is the most elastic skin layer among the skin layers.

In particular, as we age, wrinkles appear on the skin, which is said to be due to the decrease in collagen in the dermal layer.

Epidermal layer

an image of epidermis layer of skin

The epidermal layer is the part that we can touch with our hands and is located at the outermost part of the skin. The epidermis is the thinnest of the three skin layers and functions to protect the skin from external bacterial invasion and irritation. It also acts as a barrier to the evaporation of water in the body.

The epidermis is made up of four layers within it:

1. Stratum corneum

2. Granular layer

3. The visible layer

4. Basal layer

Let's take a look at the four layers above.

1. Stratum corneum

The stratum corneum is the outermost layer of the epidermis. It is hard, dry, thin shell of keratinocytes that forms keratin. The stratum corneum is composed of keratinocytes and dead cells that divide. It is contained in about 90% of the stratum corneum and made up of 20-25 layers. The thickness of the stratum corneum varies depending on the body part, and areas such as the palms of the hands and soles of the feet have a very thick stratum corneum, allowing them to withstand physical shock, friction, or trauma received in everyday life. Although the stratum corneum is composed of dead cells without nuclei and a protein called keratin, it occupies the most important role in the skin's protective function. This stratum corneum prevents bacteria or external toxic substances from invading the body, and also serves as an important barrier to prevent moisture from escaping from the inside of the body. The stratum corneum contains natural moisturizing factors and contains 10-20% moisture. If the moisture content falls below 10%, the skin dries out and becomes rough and cracked. In general, the moisture content of the stratum corneum is higher in younger skin, and the moisture content of the stratum corneum decreases with age.

2. Granular layer

The granular layer is the layer just below the stratum corneum. Keratin is formed here and tightly binds keratin-forming cells to prevent moisture evaporation. Thus, it prevents the skin from drying out. It is made up of small granule-shaped cells, and the cells of this granular layer are composed of 2-5 layers of flat, diamond-shaped nucleated cells, arranged parallel to the skin surface. The granular layer acts as a barrier against the penetration of foreign substances, especially water, and prevents moisture evaporation from inside the skin. The keratin protein aggregates appear dark in color, and this aggregated keratin protein is called keratohyalin. Keratohyalin granules are unique granules found in the granular layer and are mainly composed of proteins containing a lot of sulfur.

3. The visible layer

This is the visible layer, also called the polar layer. Langerhans cells, which play an important role in immunity, exist here. The prickly layer is composed of prickly cells. These prickly cells act as a bridge between cells, providing nutrients and oxygen to the cells and discharging waste products.

4. Basal layer

The basal layer is the lowest layer of the epidermis. The basal layer contains Langerhans cells, which are important for immune function. Keratinocytes formed in the basal layer receive nutrients and oxygen from the blood and help cell division. The basal layer, located in the deepest part of the epidermis, is a single layer and forms a wavy boundary with the dermis. The basal cells of the basal layer are living cells that produce new cells through active cell division and exist together with melanocytes. Basal cells and melanocytes exist in a ratio of 4:1 or 10:1, and keratin fibrils are produced and move to a new layer through cell division. Cell division in the basal layer is most active during sleep at night, so sufficient rest during the night is very important. The basal layer contains melanocytes that produce melanin pigment, which determines the color of the skin. Skin color is determined by the amount of melanin produced from melanocytes. If the amount of melanin is small, the skin becomes white, and if the amount of melanin is large, the skin becomes dark brown.

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