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Skin Expertise
  About the SKIN - The Skin & Its Cells  
The skin is the largest human organ. It covers between 1.5 and 2 m² and accounts for about one sixth of total body weight.

The skin consists of three functional layers : The skin performs various functions such as temperature regulation and insulation, energy storage, sensory perception and protection from environmental influences such as fungi, bacteria and (UV) radiation. We supply Skin Whitening Tablets in India

Skin

Epidermis :
  • Is the outermost skin layer.
  • The epidermis forms the actual protective covering against environment. Its average thickness is 0.1 mm. On the face it is only 0.02 mm, while on the soles of the feet between 1 and 5 mm.
  • On the skin surface are the sweat gland pores (100-200/cm2) and the openings of the sebaceous glands (50-100/cm2).
Their secretions provide the skin with moisture and lipids and thus maintain the hydrolipid film. The epidermis itself has no blood vessels, so nutrients are supplied through the fine blood vessels in the dermal papillae.

The epidermis consists of up to 90 percent keratinocytes, the actual epidermal cells that are held together by what are called desmosomes. The epidermis has five different layers:
  1. Horny layer (stratum corneum)
  2. Clear layer (stratum lucidum)
  3. Granular layer (stratum granulosum)
  4. Prickle-cell layer (stratum spinosum)
  5. Basal layer (stratum basale)
Schematic diagram of the epidermis:
During differentiation the basal cells change into flat horny skin cells without nuclei.

Skin Epidermis

Basal layer (stratum basale)
The stratum basale is the bottom layer of the epidermis. The basal cells lie directly on the basal membrane, which forms a well-defined border between the dermis and epidermis. The basal cells act as mother cells, ensuring continuous regeneration of the skin by cell division (proliferation). The daughter cells are slowly pushed by the actively dividing cells into the outer lying layers where they go through various stages of development. Also found in the basal layer are the melanocytes, which are the pigment-producing cells.

Prickle-cell layer (stratum spinosum)
The stratum spinosum (spino = thorn, prickle/lat.) or prickle-cell layer lies above the basal layer. In it the membrane-bounded vacuoles (Odland bodies), become visible for the first time. They contain the precursors of the epidermal lipids in the form of lamellar (arranged in thin plates) bilayer lipid membranes.

Granular layer (stratum granulosum)
Above the prickle-cell layer is the stratum granulosum (granula = grain/Lat.), where cornification (keratinization) of the keratinocytes begins. It gets its name from its appearance, which is due to the presence of what are known as keratohyaline granules which are composed primarily of the protein profilaggrin and keratin intermediate filaments.

Clear layer (stratum lucidium)
The stratum lucidium is also called the clear layer as it is highly refractive. The cells have been extremely flattened and are closely packed. The cell boundaries are no longer recognizable.

Horny layer (stratum corneum)
The stratum corneum (cornea = horny skin/Lat.) is the uppermost layer of the epidermis. Between the cornified cells (corneocytes) lie the epidermal lipids. The horny layer - especially the bottom third - forms the permeability barrier, which is the skin's true barrier against exogenous factors and endogenous water loss.

The functions of the horny layer
Skin Epidermis

Formation and function of the epidermal lipids
The lipid composition and moisture content of the epidermis change with increasing differentiation of the skin cells. Lipids are formed in the Golgi apparatus of the keratinocytes. Stored in the membrane-coated vacuoles known as the Odland bodies are the precursors of the skin-specific barrier lipids in the form of lamellar bilayer lipid membranes. The contents of these Odland bodies are released into the extracellular space by exocytosis where they are further processed to epidermal lipids: As a horny cell cement these bilayer lipid membranes give the horny layer stability.

At the same time these intercellular lipid membranes are the decisive permeability barrier of the horny layer: Regulation of the water and fluid content is its most important function, as elasticity and firmness of the horny layer depend on moisture content.

Composition of the epidermal lipids
Ceramides form the largest fraction of lipids in the horny layer with 40 percent. Also found are free fatty acids (25%) and cholesterol (25%) as well as cholesteryl sulphate. The ceramides are primarily responsible for the barrier-forming and moisture-binding functions of this complex lipid mixture. Chemically, the ceramides are a group of sphingolipids. These are compounds formed from high-molecular weight alcohols, primarily sphingosine, and various fatty acids such as linoleic acid.

The permeability barrier
The epidermal lipids comprise 10 to 30 percent of the total volume of the horny layer (stratum corneum). That means they make up 100 to 200 times more of the total volume of intercellular substance than in other tissues. Accordingly, the stratum corneum makes an effective permeability barrier which performs two important functions:
  • It prevents invasion by microorganisms and certain substances such as chemicals and allergens.
  • It minimizes transepidermal water loss (TEWL) and thus protects the body from dehydration.
If horny cell layers are removed and with them the epidermal lipids, the skin becomes more permeable to water (TEWL) and other substances, including toxins and allergens.

Natural moisturizing factors (NMF)
The ability of the skin to store water depends in large part on the make-up of the barrier lipids in the horny layer. The protein structure of the horny cells, including the presence of the amino acid arginine, also influences the water-binding capacity of the skin. These substances, which occur naturally in the body and retain water in the horny layer, are called natural moisturizing factors (NMF). They originate from the cornification process (differentiation) of keratinocytes (e.g. pyrrolidine carboxylic acid) and from sweat and sebum (e.g. urea, salts, and organic acids).

Desquamation and skin renewal
Towards the surface the horny layer of the skin becomes increasingly fragile. The individual cells split apart from each other (pars disjunctiva), loosen and are sloughed off unnoticed as scales. This unperceived, continuous process is called desquamation. An adult human sheds approximately 10 grams of skin scales a day.

Dermis
  • The dermis forms a well-defined border with the epidermis and a less well-defined border with the subcutis (subcutaneous fatty tissue).
  • The stratum papillare forms a well-defined, wave-shaped border with the epidermis.
    Skin Epidermis
Formation and function of the dermis

Stratum papillare and stratum reticulare
The stratum reticulare (stratum = covering, layer; reticular = net-like/Lat.) makes up the lower part of the dermis and shows a continuous transition to the subcutis below. The stratum papillare (papillae = protuberance/Lat.) is the upper layer. It forms the sharp, wave-shaped border with the epidermis. The wavy structure increases the contact area with the epidermis, thus ensuring optimal nourishment of the deepest epithelial layer of the epidermis - the basal cells - by way of the blood vessels running through the papillae.

The connective tissue of the dermis
The main constituent of the dermis is the proteinous connective tissue made up of arc-shaped, elastic fibres and undulated, nearly inelastic collagen fibres. These are responsible for the high elasticity and tensile strength of the dermis. Young collagen fibre-glycosaminoglycan complexes can bind large amounts of water and so determine the high intrinsic tension of young skin. As the skin ages, the interweaving of the collagen fibres increases and the water-binding capacity decreases. The skin tends to wrinkle.

Connective tissue, glycosaminoglycans and water-binding capacity
The interfibre space of the dermal fibre network contains a sort of "filling" made of long chains of sugar molecules (polysaccharides; poly = many, sacchar = sugar/Gk.). These are known as glycosaminoglycans (also mucopolysaccharides). With the help of fibronectins, a type of "glue", they bind to the proteinous connective tissue matrix to form proteoglycans, which can bind water molecules. This gel-like mass functions like a sponge. Under pressure it can expel the bound water and in a reverse process take it up again. This process probably helps supply the dermis with nutrients.

Hyaluronic acid (hyalo = glass/Gk.)
belongs to the group of glycosaminoglycans and so is part of the water-binding unit of the connective tissue. Glycosaminoglycans are constantly being produced and degraded. In contrast, new collagen fibres are produced only when needed, such as when the skin is injured.

Other constituents
Other constituents of the dermis are various types of cells such as the fibroblasts, mast cells and other tissue cells, as well as numerous blood and lymph vessels, nerve endings, hot and cold receptors as well as tactile sensory organs.

The Subcutis (Subcutaneous Fatty Tissue)

The subcutis (sub = under; cutis = skin/Lat.) is the fatty tissue below the skin. It consists of spongy connective tissue interspersed with energy-storing adipocytes (fat cells).

Formation and function of the Subcutis
Fat cell clusters - Fat cells are grouped together in large cushion-like clusters held in place by collagen fibres called connective tissue septa or sheaths.

Skin

Nourishment, insulation and padding
The subcutis is heavily interlaced with blood vessels, ensuring quick delivery of stored nutrients as needed. The functions carried out by the subcutaneous fatty tissue, apart from storage of nutrients in the form of liquid fats, include insulation of the body from the cold and shock absorption. On the palms of the hands, the soles of the feet and the buttocks the fat padding is almost exclusively for shock absorption.

Fat distribution in men and women
The fat content of the subcutis is not the same in all body regions. Also men and women differ in the distribution of subcutaneous fat. For example, cellulite – due to a special arrangement of the subcutaneous fat tissue septa and preferential fat storage on the hips, thighs and buttocks - occurs mostly in women. Men on the other hand tend to store fat on the torso.

Skin Appendages

The epidermal appendages include the nails, hair and glands (glandulae cutis). They arise from invaginations of the epidermis into the dermis.

Nails
The nails are horny plates firmly attached to the nail bed. They are about 0.5 mm thick and consist of the front free edge - the body of the nail - and the nail matrix, which is embedded in the proximal nail fold.

Skin

Hair
The hair is divided into the protruding hair shaft and the hair root. The root thickens at the end to become a bulb (bulbus), which together with the underlying dermal hair papillae is responsible for the nourishment, development and growth of hair.

A dermal sheath of connective tissue surrounds the whole hair root and together these form a unit known as the hair follicle. The sebaceous glands open into the infundibular part of the hair follicle.

Glandulae cutis
The glands of the skin (glandulae cutis) include the sweat, scent, sebaceous and milk glands. The sebaceous glands are nearly always connected to hair follicles, which deliver the lipid-containing secretion to the surface through their funnel shaped openings. The size of the sebaceous glands and therefore the amount of sebum itself differ according to body region. The glands found on the face, for example, are bigger than those found on the arms or legs. An important influencing factor in sebaceous gland activity is the androgens.

Sebaceous and sweat glands are exocrine glands
(exo = outer, external/Gk.), which means they deliver their secretion directly to a surface such as the skin. In the case of the sebaceous glands this occurs with complete disintegration of lipid-rich cells. They are continually replaced through division of the basal cells (holocrine glands). In the case of apocrine glands like the mammary glands or the sweat glands of the axilla (underarm) only the outer parts of the cell body are lost with the secretion. The cells of the eccrine glands like the small sweat glands of the skin show no loss of cytoplasm after the secretion process. Together with the sweat glands, the sebaceous glands provide vital substances that - along with the epidermal lipids - form the hydrolipid film.