SKIN BASIC STRUCTURE AND FUNCTIONS OF SKIN

• Skin is a continuous organ,sensoryorgan,and heaviest
• Its pH is about 5-6.5,acidicmedium.As it is acidic it stops the entry of microorganisms.
• It acts as a barrier for internal organs.

Types of skin:
1. Epidermis
2. Dermis
3. Sub-cutaneous
4. Skin appendages

1) EPIDERMIS:
• It is the outer most layer of skin
• Multilayered
• It has different thickness 0.8 -hands and feet , 0.06-eyelids

Types of epidermis:
 Stratum corneum:
 it contains dead keratinized cells ,10micrometers,contains columnar highly organized in ventricular column .
 relative humidity 15-20%.
 when creams are applied the stratum corneum is highly hydrated where evaporation of water takes place.
 when the skin is dried it forms brittle and breakdown called as chapped lips.

Stratum corneum is divided into 2 types:
• Horny pads: it is 40 times thicker than that of membranous stratum corneum.
- Weight bearing and fraction.
• Membranous stratum corneum: it is flexible ,impermeable in nature.
Responsible for percutaneous absorption of chemical substances & also has a tendency of shedding of stratum corneum is about 0.5-1 kg.

 Stratum lucidum:
 It is a poorly staining hyaline zone of palms of hand and soles of feet.
 Non-nucleated.
 Thin ,translucent layer.

 Stratum granulosum:
 It is a granular layer .
 It has a keratin composed of keratinized cells called keratinocytes, which produces keratohyalinegranules ,which are responsible for basic staining.
 Keratinocytes have an intense biochemical activity.

 Stratum spinosum:
 It is also called as prickle cell layer.
 As basal cells moves upwards the cells of these become flattened and nuclei shrinks ,which result in prickle cells.
 Prickle cells along with adjacent cells & cytoplasm forming inter connected bridge called as “desmosomes” & responsible for integrity of epidermis.

 Stratum germinatum:
 This layer contains basal cells.
 6 micrometer in thickness,nucleated and columnar
 The cells that are produced are melanocytes ,which secrete melanin(pigment)
 This melanin helps in pigmentation and protection against the radiations.

2) DERMIS:
It is present in between layers of epidermis & subcutaneous.
 It comprises of dense nature or matter of structural proteins such as elastin, reticulin & collagen.
 These are dispersed in semigel matrix of mucopolysaccharides as ground substance , which gives elasticity.
 It is 0.2-0.3 micrometer in thickness.

3) SUBCUTANEOUS:
 This layer is present below dermis.
 The sheet of fat is comprised of areolar tissue.
 That is superficial fascia ,which is attached to dermis.
 In this layer large arteries and veins are present.

4) SKIN APPENDAGES:
 This contains hair follicles, sebaceous glands,sweatglands.
 This is present all over the body except lips ,palms,soles etc.
 Sebaceous glands: it contains sebum comprised of fats, proteins, inorganic salts, cholesterol .

 Sweat glands:
It is divided into 2 types.
• Eccrine glands: these are large ,coiledglands,of 100-200micrometers thickness
They are also called as “salty glands” as they secrete very dilute solution of salt.
It controls heat and temperature.
• Apocrine glands: these are present in anogenital areas such as nipples ,arm pits .

Essential fatty acids are:
Lineolicacid ,arachidonic acid which act as barrier function.

FUNCTIONS OF SKIN:
• It protects internal organs.
• It regulates body temperature
• It regulates blood pressure
• It protects against external stimuli such as radiation ,heat,cold.
• It helps in excretion of metabolic wastes
• It helps in containiment of body fluids
• Proteinase enzyme(anti-inflammatory action in cell injury)
• Metabolises VitD-D3, calcitriole
• Free fatty acids-shows fungicidal and bactericidal activity.
• Responsible for biochemical synthesis.
• Reception of stimuli.