The skin reflects origin, lifestyle, age and state of health. Skin color tone and evenness, pigmentation as well as skin surface characteristics are sign of skin’s health. The cosmetics and pharmaceutical industry offer a vast armamentarium of skin care products and procedure to clean, soothe, restore reinforce, protect and treat our skin to keep it in “Good Condition”. It is the largest organ of the body covers entire body’s surface and form first barrier against pathogens, UV lights, chemicals and provide mechanical barrier to injury.
The skin bearing hair, sebaceous glands, sweat glands. The skin is composed of three primary layers: epidermis, dermis and subcutaneous tissue. Each layer presents special character and functions.
Epidermis: Epidermis is the outermost layer of the skin with a thickness of 0.2mm on average. The epidermis further divided into five layers, beginning with the outermost layer stratum corneum, Stratum Lucidum, granular cell layer, prickle cell layer and basal cell layer. Epidermis has following four layers:
1. Stratum corneum- It is the outermost layer of epidermis, has multifarious functions to repel the water, act as bacterial and viral guard, mitigating exogenous oxidants that can damage components of skin via antioxidant etc., This layer composes of many dead skin cells which contain Keratin fibrous protein.
2. Stratum Lucidum- This layer is found only on the palms of the hands, fingertips and soles of the feet. Stratum lucidum is a smooth, seemingly translucent layer of the epidermis located just below the stratum corneum and densely packed with keratohyalin derived protein eleiden.
3. Stratum Granulosum- The Stratum Granulosum has grainy appearance due to keratinocytes pushed from the stratum spinosum. In this layer the keratin protein production occurs. The nuclei and other cell organelles disintegrate as the cells die, leaving behind the keratin, keratohyalin and cell membranes that will form upper layers and the accessory structure of hair and nails.
4. Stratum spinosum- The stratum spinosum layer has the spiny appearance is happens because of the producing cell processes that join the cells via a structure called a desmosome.
5. Stratum Basale- This is the layer where the keratinocytes are formed, it is also known as stratum germinativum. The cells in the stratum basale bond to dermis via intertwining collagen fibers, refer to as basement membrane. Stratum basale have finger like projection or fold known as the dermal papilla. Two other cell types are found dispersed among the basal cells in stratum basale. First Merkel cell which function as a receptor and is responsible for stimulating sensory nerves that the brain perceives as touch. These are huge on the surface of hands and feet. Second is a Melanocyte a cell that produces the pigment melanin. It gives hair and skin its color, also protect living cells from UV damage.
Dermis: The dermis is connective tissue layer sandwiched between the epidermis and subcutaneous tissue. It is fibrous structure composed of collagen, elastic tissue, vasculature, nerve endings, hair follicles and glands. The role of dermis is to support and protect the skin and deeper layers, assist in thermoregulation and aid in sensation. The primary cells are fibroblast and other histiocytes, mast cells and adipocytes also play an important role in maintaining the normal structure and function of the dermis.
Fig. The Skin
Subcutaneous Tissue: It is the deepest layer of the skin and it also called subcutis or hypodermis which contains blood vessels and nerves. The subcutis contains a layer of fat, it maintains the body temperature. This layer also acts as cushion against physical trauma to internal organs.
Hair: Hair is one of the characteristic features of the mammals, it is a derivative of the epidermis and consist of two distinct part- the follicle and the hair shaft. The hair follicle is essential unit of generation of hair. Hair shaft has a continuous growth and rest sequence named hair cycle. For topical products hair rout is the important way of drug delivery.
Functions of hair follicle to skin:
Hair follicle cells secret keratinocyte growth promoting factors that helps to stimulate wound healing.
Hair follicles induce new blood capillaries from pre-existing blood vessels.
Hair follicles retain immune privilege and immunosurveillance properties.
It may provide a conduit for pathogens.
Hair follicles are modulated by or may modulate the neuroendocrine system.
It retains the stem cells.
Functions of hair shaft to skin:
It increases and maintain the beauty of the skin.
Shaft of scalp hair and eyebrows prevent from entering sweat into eye.
Shaft of scalp hair also prevent skin from UV rays and other external factors such as dust, dirt, pollutant etc.,
Wholes body’s hairs shaft help to maintain the temperature of the skin.
Sebaceous Gland (SG):
Sebaceous glands are uni/multilobular entities usually associated with hair follicles which form a structure known as the pilosebaceous unit. The most important function of SG is producing the sebum and maintains naturally the health of skin.
Importance of SG for skin:
Sebum contains glycerol which is necessary for skin hydration and as an occlusive moisturizing agent.
Vit E has high anti-oxidant property which is found in sebum and help to reduce the skin oxidation.
Sebum possesses anti-microbial property due to the action of oleic & palmitoleic acid.
Protect keratinocytes from UV rays.
Regulations of steroidogenesis, neurogenesis with selective control on the action of cutaneous hormones.
Sweat Glands:
Sweat gland basically known as sudoriferous gland divided in two glands the apocrine glands and the eccrine glands. The apocrine glands present in the groin area and the armpits, produces thicker form of sweat, which is responsible for body after bacterial contact. Eccrine glands are huge on face, palm of hand, sole of the feet and other part of body. Sweat is mixture of water, salt, urea, uric acid, ammonia, amino acids, simple sugars and vitamins. Major function of sweat is to control the body's temperature.
Anti-Microbial Peptides: It is one of the most interesting and important topics because of their involvement in the innate immune system of human skin. Anti-Microbial peptids show broad spectrum activity against bacteria, viruses and fungi. Cathelicidin and defensin are the two major groups of anti-microbial peptides. Cathelicidin has been identified in the keratinocyte of human skin at area of inflammation as well as in eccrine and salivary glands. Defensin is also expressed in the human keratinocyte and mucous membranes.
Task of the SKIN
· The most important task of skin is protecting form external factors such as mechanical chemical and microbial influences. Also, guard from allergens, UV rays and other environmental conditions like cold, heat and dehydration.
· The skin regulates the temperature via dilation of blood vessels and by sweating as well as balance the water. The sebum forms an important protective hydro lipid mantle on surface of skin.
· It is involved in the metabolism of whole organism such synthesis of Vit-D and biotransformation of some chemicals.
· The skin reacts to feeling such as horror, anxiety and panic.
Comments