The skin is the largest organ of the body. It has a complex structure. Because, it performs many important functions.
This includes containment of body fluids, and tissues, disposal of biochemical waste, regulation of body temperature etc.
Structure of Skin:-
Skin contains several chemical substances with specific functions like keratin, lipids, fatty acids, proteinase, etc.
Keratin is produce from polypeptides in the cytoplasm of epidermal cells. It is due to a high energy system at the granular layer.
Sebum is the product of the sebaceous glands and consists of triglycerides, free fatty acids, waxes, sterols, squalene and paraffins. But, free fatty acids are responsible for bactericidal and fungicidal activities.
Also, it contains two essential fatty acids, called linoleic acid and arachidonic acid. They play an important role in regulating the barrier functions.
Skin synthesizes on steroids, vitamin D3, that subsequently gets converted to the hormone calcitriol which is important to normal calcium metabolism.
Human skin has two main layers. One is epidermis, and second is dermis
- The epidermis is made up of several rows of living cells, covered with a horny layer of dead cells.
- These are constantly being shed and replaced by new cells from the lower layers.
- The process by which dead cells are shed is known as ‘desquamation.’
- The epidermis comprises of five distinct and separate layers.
1) Stratum Corneum:-
At the final stage of differentiation, epidermal cells construct the most superficial layer of the epidermis, that is called stratum Corneum. On the general body areas the membrane provides about 10-15 layers of much flattened, keratinized dead cells, stacking them in highly organized units of vertical columns.
2) Stratum Lucidum:-
In the palm of the hands and the sole of the foot, hyaline zone forms a thin, translucent layer above the granular layer. This region is the stratum lucidum. The cells are non nuclear.
3) Stratum Granulosum (granular layer):-
This layer lies above the keratinocytes. They manufacture basic staining particles, the keratin hyaline granules. The dynamic operation manufactures the keratin to form the horny layer by an active rather by a degenerative process.
4) Stratum Spinosum:-
The cell of this layer are produced by morphological and histochemical alteration of the cells of basal layer as they move upward. The cells flatten and their nuclei shrink. They are called prickle cells. This prickle form intercellular bridges, the desmosomes. These links maintain the integrity of the epidermis.
5) Stratum Germinativum:-
The basal cell are nucleated, columnar and about 6µm wide, with their long axis at right angle to the dermo epidermal junction. They are connected by cytoplasmic intercellular bridges.
Mitosis of the basal cells constantly renews the epidermis. And this proliferation in healthy skin balances the loss of dead horny cells from the surface. Thus the thickness of epidermis remains constant.
- The dermis supports to the epidermis. They play an important role in determining the contours.
- The dermis is form of tough, flexible connective tissue.
- The structural network of collagen and elastin fibers that supports and are responsible for its tone, firmness and resilience.
- The condition of the network of collagen and elastin fibers determines whether the skin is firm and without lines, or wrinkled, loose and sagging.
- The dermis contains sweat and sebaceous glands. The surface ends of the oil glands form the pores of the skin.
- The sebaceous glands secrete sebum, an oily, slightly acidic film, which helps to lubricate the skin and keep it healthy.
- The sebaceous glands are more numerous on the face and back.
- The dermis also contains the skin’s blood vessels that supply oxygen and nutrients to the skin.
- The sweat glands eliminate wastes and regulate body temperature.
Collagen And Elastin:-
- The protein fibers that make up the dermis are collagen and elastin.
- They give the skin elasticity and also resilience.
- The degeneration of these fibers causes the skin to sag and develop lines and wrinkles.
The Acid Mantle:-
- The sebum or oil secreted by the sebaceous glands
- Along with sweat, from a protective film on the skin surface.
- It is known as the acid mantle.
- The film is acidic in reaction and protection the skin from bacterial activity.
- Chemical, caustic and alkaline substances can alter the pH level of the skin and predispose it to problems.
Functions of the skin
The main function of the skin is that of protection, but it also per-forms several important functions.
- The skin is waterproof.
- It not only contains body fluids, but pre-vents large quantities of fluid from entering.
- The outer layer of the skin protects us from bacterial activity.
- While, the inner layer cushions the body from minor injuries.
- The skin has nerve endings that make us aware of sensations of heat, cold, pressure, pain and other influences.
3) Regulation of heat:-
- The sweat glands of the body regulate body temperature.
- Sweat evaporates and keeps the body at right temperature.
- The blood vessels in the dermis also help at the body to adapt to changes in outside temperature.
- When the superficial capillaries expand then surface heat get reduce and body temperature becomes low.
- When it is necessary to retain heat, the blood vessels contract, or constrict. And blood flows more freely.
4) Elimination of wastes:-
- The skin eliminates waste products through the sweat glands and deposits them on the skin-surface.
- The sweat deposit consists of cellular waste, fatty substances, water and salt.
5) Secretion And Absorption:-
- Sebum and perspiration form a film on the face, keeping the skin healthy and supple.
- The hair follicles and the openings of the sebaceous glands are capable of absorption.
- The penetration of substances, like cosmetic products, get affect due to the condition of the epidermis.
- When there is a build-up of dead cells on the skin’s surface, penetration and absorption are poor.
The skin’s type you have depends on the activity of the sebaceous, or oil producing glands.
1) Normal Skin:-
- Normal skin’s pH is 5.5 skin. 5.5 pH of the skin is ideal.
- It is neither oily, nor dry.
- It has a translucent, soft, smooth texture and a healthy glow.
2) Dry Skin:-
- The sebaceous glands are less active.
- The skin lacks both oil and moisture.
- It is fine texture and fragile.
- As it is vulnerable to changes in temperature and humidity.
- It flakes easily and develops early lines and wrinkles.
3) Oily Skin:-
- The sebaceous glands are over active.
- The skin has a greasy shine.
- The texture is coarse, due to enlarged pores.
- It is prone to clogged pores, blackheads, pimples and acne.
4) Combination Skin:-
- The skin has a greasy area, while surrounding areas are dry.
- The T-zone, consisting of forehead, nose and chin are usually greasy.
- The cheeks and area around the eyes are dry.
- This is the most common skin’s type.