Its not every day that we go into Skin Biology, but if you want to understand how skin aging happens, and how skincare products help to reduce aging, then its important to understand how the skin looks and works.
Its hard to realize that skin is an organ. In fact its the largest organ of the human body called the integumentary system. It protects the internal organs, as well as muscles bones and ligaments. Our skin forms a protective barrier against the environment. It blocks our internal bodies for us against germs and other organisms from getting inside. It is the skin that helps keep our body temperature
An average adult has 18 to 20 square feet of skin covering their bodies. It weights approximately 6 pounds. One square centimeter of skin is made up of 6 million cells. Skin on the human body has 5,000 sensory points. It consists of 100 sweat glands located throughout the skin system and 15 sebaceous glands. Human skin is about 0.07 inches or approximately 2mm thick.
Skin is composed of 3 primary layers with multiple sublayers.
The outer most layer is the Epidermis, the middle layer is the Dermis which also includes connective tissue and the Subcutaneous or Hypo-Dermis is the bottom layer. The Epidermis is a tough protective layer that contains the melanin. It is melanin that gives us out color and helps protect us against the damaging sun rays. The second layer found under the Epidermis is the Dermis which
contains nerve endings, sweat and oil glands and hair follicles. The Hypo Dermis is the layer that is comprised of adipose (fat) tissue as well as the blood vessels.
Human skin constantly regenerates itself. To start the process of regeneration; a cell is generated in the dermis of the skin first. The same cell migrates up towards the Epidermis over a two week traveling period. At the end of the two weeks it will reach the bottom layer of the Epidermis. This cell continues moving until upward until it reaches the surface of the Epidermis. It spends two more weeks in
the Epidermis flattening out where it eventually dies and sheds. The process of cellular migration from the Dermis to the Epidermis repeats over and over again. It is a continuous process that occurs our whole lives. We shed two to three billion skin cells on a daily basis.
The human body goes all out to replace cells as they shed on a monthly basis. This is because the skin is the first line of defense against dehydration, infection, injury and extremes of temperature. The skin is an unbroken surface that protects things from entering the body or penetrating and going throughout our systems. Skin cells detoxify harmful substances that try to enter our bodies much in the
same way the liver does. They both filter and help our bodies remove the toxins so the toxins can be eliminated as waste. Skin can also absorb and utilize nutrients that are topically applied to it. Lets look at each layer now independently.
This is the skin layer between you and the external world. It consists of three types of cells. The total thickness of the epidermis is between 0.5 to 1 mm. The cells of the Epidermis are keratinocytes, melanocytes and Langerhans cells. The keratinocytes are the predominant cells in the epidermis and make up the protein Keratin.
At the lowest layer of the epidermis are immature keratinocytes that keep dividing. As the cells divide they lose moisture and flatten out; all the while moving upward towards the outer most layer of the Epidermis . The outer most upper layer of the Epidermis is called the Stratum Corneum. At the end of their life span the cells reach the outer most layer of the epidermis where they die. This layer is made up of primarily dead keratinocytes, keratin (which is hardened protein) and lipids which together form a protective crust. The dead cells from this outer most layer constantly slough off only to be replaced with the ones that come to the surface. Skin completely renews its self every 3 to 5 weeks.
Melanocytes are the cells responsible for producing melanin which is the pigment responsible for our skin tones and color. The more melanin in our skin the darker we are. Genetics also play a part in our skin tones.
The Langerhans are responsible for our immunity through the skin. They are the ones that prevent unwanted substances from penetrating our skins and entering our bodies. How we treat our Epidermis shows to the world how young we look as a result. Although wrinkles develop on the lower skin levels, how fresh we look is based on the epidermis. The epidermis is the layer that helps hold and absorb moisture to keep us looking young.
The Layers of the Epidermis
As I mentioned previously the Epidermis is made up of sub layers. We already looked at the stratum corneum or outer most layer. That layer is made up of dead cells and protein. The stratum corneum layer has a buildup of the protein Keratin. Keratin is the protein that is important to skin, nails and hair.
Translucent or transitional layer- This is a translucent thin layer of cells. Sometimes this layer is seen in thick skinned people.
Suprabasal layers- 3 to 5 layers of flattened cells. Below them are cubed shaped cells containing little pieces of keratin traces.
Basal or cell division layer- this is the layer where the cells undergo division to travel to renew and replenish the upper layers. This is the bottom most layer of the Epidermis.
Next we have the Dermis Level.
This is the middle layer located between the Epidermis and Subcutaneous tissue. his is the thickest of the skin layers. It is made of tight meshed collagen and elastin fibers. These two elements are crucial skin proteins. Collagen is a protein that is responsible for structural support and elastin for skin resilience.
The primary cells in the dermis are fibroblasts. Fibroblasts are very important in overall skin health. The dermis contains capillaries which supply oxygen and nourishment to the skin and lymph nodes which are depots for immune system cells which help fight infections from entering the body.
The dermis houses sebaceous and sweat glands, hair follicles, a small number of nerve and muscle cells. The sebaceous glands located around the hair follicles lubricate the skin with an oil substance called sebum. Sebum lubricates and water proofs the skin and hair. As we age we produce less sebum making the skin prone to drying and wrinkling. On the other hand over production of Sebum as with adolescents contributes to acne.
The dermis is responsible for the structural integrity, the elasticity and resilience of the skin. This layer is where we get our wrinkles from. The only way wrinkle creams will work is if they reach this layer of the skin.
Lastly we have the Subcutaneous layer of the skin. This is the innermost layer of skin and is made up mostly of fatty tissue. The subcutaneous layer is made up of mostly fat cells. This layer serves as a shock absorber and heat insulator due to the fat cells and tissue.
It protects the underlying tissue from cold and trauma. Sweat glands and miniscule muscles that attach to hair follicles originate here in this layer.
When we age we tend to lose subcutaneous tissue resulting in facial sagging and accentuated wrinkles. Many people go to cosmetic doctors to have fat injected back into their skin to try and maintain a youthful appearance because of the loss of ubcutaneous tissue.
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