The human skin consists of two major structures:
* Epidermis
Protein Bar
* Dermis
The Epidermis
The Epidermis is further subdivided into 5 Layers (from deepest to most superficial layer):
* Stratum basale
* Stratum spinosum
* Stratum granulosum
* Stratum lucidum
* Stratum corneum
The Stratum basale (also called Stratum germinativum): This is the deepest layer of the epidermis and it is here that new cells are generated for the renewal of the epidermal layers of the skin. A process of cell division referred to as mitotic division is responsible for the generation of the new epidermal skin cells. After the mitotic division (cell division leading to the formation of a new cell) a newly formed cell will undergo a progressive maturation called keratinisation as it migrates to the surface of the skin (1).
The Stratum spinosum: The cells that divide in the stratum germinativum soon begin to accumulate many desmosomes (structures that join adjacent cells together) on their outer surface (1).
The Stratum granulosum: As keratinocyes (these are the basic cell of which the epidermis is composed) progressively mature they accumulate a protein called keratin (this process is called keratinisation). In addition, the cells of the stratum granulosum accumulate dense basophilic keratohyalin granules (Granules found in living cells of keratinizing epithelia) (1).
The Stratum lucidum: This is the second layer of the epidermis and varies in thickness throughout the body depending mainly on frictional forces and is thickest on the palms of the hands and soles of the feet (1).
The Stratum corneum: This layer consists of primarily dead skin cells. As a cell accumulates keratinohyalin granules, it is thought that rupture of lysosomal membranes (membrane covering lysosomal enzymes) release lysosomal enzymes (Lysosomal enzymes are those enzymes which are responsible for breaking down complex chemicals within a cell which have expended their useful life) that eventually cause cell death (5). The dead and dying cells filled with mature keratin form the stratum corneum .
Skin Renewal Process In the Epidermis
The epidermis is composed of stratified squamous epithelium (cells) and contains four principal types of cells. About 90% of the epidermal cells are keratinocytes (i.e.: cells with finger-like or 'horny' projections). They produce the protein keratin. Keratin helps waterproof and protect the skin and underlying tissues (2).
Keratinocytes in the stratum basale of the epidermis can undergo mitosis (cell division). The formation of new cells in this basal layer gradually pushes previously formed cells upward through the stratum spinosum. As keratinocytes approach the surface of the epidermis, they accumulate intracellular keratin and secrete a waxy material into the intercellular space; these changes are visible in the stratum granulosum, a distinctive layer which is diagnostic for a keratinized epithelium. As maturing keratinocytes seal off the intercellular spaces through which they receive nutrients, they eventually die and form the stratum corneum, a tough and relatively impermeable layer of hardened, dead cells. Eventually, as cells reach the surface, they are sloughed off. The entire epidermis above the basal layer is replenished (replaced by new cells) within about two weeks (3).
Epidermal cells
There are several cells that make up the epidermis. Although the keratinocytes are by far the most common, they are just one of the cells found in the epidermis.
Others include:
Melanocytes: The main function of melanocytes is to produce melanin, which is responsible for the colour of our skin (4).
Langerhans Cells arise from bone marrow and migrate to the epidermis. Langerhans cells interact with white blood cells called ‘helper T cells’ in immune responses and are easily damaged by UV radiation (2).
Merkel Cells: Merkel cells are located in the deepest layer (stratum basale) of the epidermis of hairless skin, where they are attached to keratinocytes by desmosomes. Merkel cells make contact with the flattened portion of the ending of a sensory neuron (nerve cell), called a tactile (Merkel) disc, and are thought to function in the sensation of touch (2).
Dermo-epidermal Junction
The Epidermis and Dermis are separated by the Dermo-Epithelial Junction. This junction holds the epidermis and dermis together and this is achieved by various fibers including collagen and desmosomes. This prevents the two layers becoming separated in areas of high shearing stress such as fingertips, palms of the hands and soles of the feet.
The Dermis
The Dermis consists of two sub-layers:
* The Papillary dermis and
* The Reticular dermis
The Papillary dermis (sub-epithelial layer) includes areolar connective tissue, dermal papillae (finger like projections that increase the surface area) and ridges that extend into the epidermis.
These nipple-shaped structures protrude into the epidermis, and many contain loops of capillaries (very small blood vessels). Dermal papillae cause ridges in the overlying epidermis. It is these ridges that leave fingerprints on objects that are handled (2).
The Reticular dermis consists of dense, irregular connective tissue containing interlacing bundles of collagen and coarse elastic fibers. Within the reticular region, bundles of collagen fibers interlace in a netlike manner. A small quantity of adipose tissue, hair follicles, nerves, oil glands, and the ducts of sweat glands occupy spaces between the fibers. Varying thicknesses of the reticular region contribute to differences in the thickness of skin. The combination of collagen and elastic fibers in the reticular region provides the skin with strength, extensibility, and elasticity.
The Hypodermis
The reticular region is attached to underlying organs, such as bone and muscle, by the subcutaneous layer, also called the hypodermis or superficial fascia. The subcutaneous layer also contains nerve endings called lamellated or Pacinian (pa-SIN-e-an) corpuscles that are sensitive to pressure. Nerve endings sensitive to cold are found in and just below the dermis, while those sensitive to heat are located in the middle and outer dermis (2).
Skin Care of the Epidermis, Dermo-Epithelium, Dermis and Hypodermis
Exfoliation
Exfoliation of the skin affects the epidermis. The primary function of exfoliation is to:
a) Remove dead skin cells
b) Promote new skin cell growth
c) Promote blood circulation
Exfoliating the skin's surface is an important step in the maintenance of healthy, vibrant looking skin. Products such as the Skin Renewal Gel, from Wildcrafted Herbal Products, utilises natural ingredients that gently remove the dead skin cells and nourish underlying layers. Keeping dead skin cells to a minimum, allows the skin to be able to breath better, absorb nutrients from moisturisers more easily and reduces the risk of infections such as Ring Worm and other pathogens.
In addition, removal of dead skin cells will reduce the potential for sweat glands to become blocked thus reducing white heads, blackheads and acne.
Cleansing
Following exfoliation, cleansing will remove more deep seated dirt and help free pores of possible obstruction from the stale, natural skin oils and environmental particles that become lodged in the skin's folds, wrinkles and pores.
Toning
Once the dead skin cells have been removed and the skin cleaned it is important to prevent pores from remaining open. Toning, utilises skin care products that contain astringent ingredients which will close opened pores and prevent particles from entering the pores while they are wide open.
Natural skin care products should be used at all times, as there is increasing evidence suggesting that some non-natural skin care products contain ingredients that may be harmful to your health, as they are absorbed by your skin into the blood stream.
Natural skin care products such as moisturisers and masks target the Dermo-epithelium, Dermis and Hypodermis.
Moisturisers
Moisturisers penetrate the epidermis as they are absorbed into the deeper layers of the skin and the nutrients from the herbal extracts and essential oils in these moisturisers have the ability to promote cell growth and collagen production.
Moisturisers are an important final step in your daily skin care regime. They moisturise and help protect your skin, they hydrate your skin and nourish the cells and other structures outlined above, thus helping in maintaining the health of your skin.
Clay masks
Once or twice a week, a deep cleansing mask should be used on your facial skin and neck. These masks not only help to deeply cleanse your skin, but provide important nutrients to the tissues of your skin and help to remove dead skin cells from your skin’s surface.
References:
1. [http://www.meddean.luc.edu/lumen/MedEd/medicine/dermatology/skinlsn/stspin.htm]
2. Tortora, G.J. & Grabowski, S.R. (1993) Principles of Anatomy and Physiology (7th Edition). HarperCollins College Publisher, New York. [ISBN0-06-046702-9]
3. http://www.siumed.edu/~dking2/intro/skin.htm
4. medic.med.uth.tmc.edu/Lecture/Main/integ1.htm
5. [http://www.ggc.org/Diagnostics/Biochemical/lysosomal_enyzmes.htm]
6. [http://www.ggc.org/Diagnostics/Biochemical/lysosomal_enyzmes.htm]
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