Main
 
 
 
 
 
 
 
 
 
   
 Skin Layers  Skin
The largest organ of the human body is the skin. It protects our bodies from the environment, maintains body temperature, excretes waste matter, gives sensory information to the brain and regulates body moisture.

The skin's functions :
- Protects the body against injury, heat & light radiation.
- Helps the penetration of chemical agents and invasion of microbes & microorganism.
- Regulates body temperature.
- Eliminate a number of harmful substances resulting from the metabolic activities of the intestine & the liver.
- Secretes hormones & enzymes.
- Acts as an external sensory organ.
- Plays an immunological role, by cooperation with langerhans cells.

Skin structure
The skin is a highly complex, dynamic tissue system. One square inch of the skin is composed of 19 million cells, 625 sweat glands, 90 oil glands, 65 hair follicles, 19 000 sensory cells and 4 metres of blood vessels is also home to millions of healthy micro-organisms which increase our immunity to pathogenic, or disease-causing bacteria. Thus, our desire to sterilize the skin also destroys beneficial bacteria, such as streptococcus mutans, and micrococcus luteus .
There are two types of glands housed within the skin :
1- Oil glands
2- Sweat glands
The duct of each oil gland usually opens into one hair follicle, but in some locations, there maybe more oil glands per follicle, resulting in greater oil (sebum) secretion in that area.
Each sweat gland begins in the dermal tissue as a coiled end. It continues as a single excretory tube or duct through the epidermis, and finally opens on the surface as a very tiny pore.
Cleansing the skin, means eliminating impurities from these pores, considering that perspiration is not a cleanser.

Skin layers
Skin is made up of three main layers :
1. the Epidermis
2. the Dermis and
3. the Hypodermis

The Epidermis :
The Epidermis, which thickness varies from 0-04mm to 1.6mm, is an important layer and it is the only layer we can see with our eyes and as we age, remarkable changes occur which are hidden from our view.The langerhans cells, responsible for the immunology of the skin, the melanocytes and tyrosinase enzyme, responsible for the production of melanin and color, are located in the epidermis.
This is the layer of skin to which, cleansing, exfoliating or hydrating products are applied.
The outermost layer of the epidermis is called the cornified layer, and is made of sheets of keratin, a protein, and squames, dead, flat skin cells. It is our barrier against dehydration from the environment. It receives its primary supply of moisture from the underlying tissue, since constant contact from the external environment tends to dry out the skin’s surface. When the skin is exposed to dry conditions, the cornified layer can become dry, brittle, firm and if untreated, it can crack and lead to infection. Creams create a waxy barrier to prevent dehydration and keep the skin moist and supple. Underneath the cornified layer lie six more layers of the epidermis responsible for cell generation. The life cycle of skin cells within this layer takes approximately 24-48 days, so it may take three to four weeks to the skin surface.
It is responsible for the look & the health of the skin.
It protects the skin from moisture loss & the penetration of chemical products and bacteria.
It acts as the initial barrier to oxidant assault.
It houses essential free radical scavengers such as vitamins E and C & super oxide dismutase.
It is able to create large amounts of glycosaminoglycans & ceramides.
The Epidermis holds a large amount of water. The younger the body, the more water there is in the skin. The skin's capacity to retain water decreases with age, making the skin more vulnerable to dehydration & wrinkles.
The Epidermis is also the first barrier against immunological aggressors, thanks to the langerhans cells.
Langerhans cells are ultraviolet radiation (UVR) sensitive. Even minor UVR exposure will damage the langerhans cells enough to reduce the skin's immune capaCitoes. With age, these cells also decrease in number, one reason why the elderly have higher potential rates of skin disease. In the basal sub-layer of epidermis, cells reproduce by subdivision. One cell divides into two, identical to one another and to the original parent cell. The older one is pushed upward and the younger remains. The new cells are large and supple and contain a high percentage of water. With age, this layer thins, making it difficult for the skin to retain moisture. As the cells move upward, they begin to fill with a granular substance called Keratin, lose water and flatten. Their phospholipids change to glycolipids, cholesterol & ceramides and then dead cells accumulate on the skin surface.
Ceramides play a vital role in the skin's water-retaining capacity, after being damaged from aging and sun exposure.

The Dermis :
The second layer, or dermis which is 5 to 7 times thicker than the Epidermis, lies below the epidermis and is connected to it by the basement membrane.
The Dermis consists of a thick connective membrane criss-crossed by blood vessels, lymphatic vessels, nerve fibers and many sensory nerve endings.
Collagen and Elastin protein fibers, the two main components of the dermis, act as a structural support system for the nerve fibers, hair follicles, blood vessels, and oil and sweat glands located in this layer, and also provide the skin with strength & elasticity.
It nitrites the epidermis by means of its vast network of capillaries and blood vessels.
It forms a supporting framework, composed of collagen & elastin protein fibers.
It is responsible for the skin's elasticity.
It acts as a water storage site.
It protects the body from mechanical injury.
It plays an important role in sensory perception and as an internal regulator.

The Hypodermis :
The Hypodermis, the skin's third and the last layer, connects the skin with the muscle tissues.
This layer is highly elastic and has fat cells acting as "shock absorbers", thereby supporting delicate structures such as blood vessels and nerves.

Differences in Skin Due to Sex :
Most human bodies are very alike and the differences are usually minor. The skin is no exception. The greatest difference is attributed to sex and the following observations have been made:
- Men have thicker and strengthen dermis layer.
- Men's skin is hairier somewhat coarser than women's.
- Men have more sweat glands since men are larger and have more skin.
- Male skin cells have a somewhat deeper color due to the greater amount of melanin in the skin.
- Men have greater output of sebaceous glands.
- The chemicals from the female sex glands make skin softer.
- Women have fewer and shorter body hairs, but the hair on their head is finer and grows longer.
- Many men lose hair or their hair grows gray or white and sparser.
- Race has very little effect on people's skin and may indicate only a slight variation in the distribution of skin glands.