SKIN-Anatomy and Physiology

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Presentation Transcript

SKIN : 

SKIN Largest organ of body Completely covers the body Continuous with membranes lining body orifices . Average thickness:1-2mm,0.5mm on eyelids & 6mm on palms & soles. pH-4 to 5.6 Renewal of skin takes place in 28-50 days by shedding of outer layer.

Structure of Skin : : 

Structure of Skin : There are 2 main layers of skin : EPIDERMIS DERMIS EPIDERMIS: Most superficial cellular layer of skin composed of Stratified epithilium [varies in thickness] No blood vessels Nutrition provided by capillaries of dermis Approx. thickness 0.4-1.5mm, thickest on palms & soles

LAYERS OF EPIDERMIS: : 

LAYERS OF EPIDERMIS: 1 ) Stratum Corneum: -Outer most layer, also known as horny layer, consist of dead cells called as corneocytes which provide mechanical protection to skin and barrier to water loss. # These cells lose their nucleus due to pressure , cytoplasm is flattened with fibrous protein KERATIN # These cells also contain phospholipid and glycogen. # Layers of dead cell-15-20. 2 ) Stratum lucidum: -Made up of flattened epithelial cells. # Exhibit shiny character, layer looks like homogenous translucent zone 3 ) STRATUM GRANULOSUM:-Thin layer with 2-5 layer of flattened rhomboid cells. # Cytoplasm contain granules of protein called Keratohyaline # It reduces water loss from skin. 4 ) Stratum spinosum:-Cells have spine like protoplasmic projections. 5 ) Stratum germinativum:-Thick layer made up of polygonal cells superficially and columnar or cuboidal epithelial cells in deeper parts. # Keratinocytes are stem cells which give rise to new cells formed by mitosis move towards stratum corneum continuously. # Melanocytes, scattered b/w Keratinocytes, produce pigment called Melanin which is responsible for skin color. # Some projections called Rete ridges extend down up to dermis to aid nutrition of epidermal cells and stabilize the two layers.

The cells of Epidermis include: Keratinocytes: Major building block of epidermis. Melanocytes: Large cells interspread among keratinocytes , produce melanin. Langerhans cells: Antigen presenting cells Merkel cells: Represent special nerve endings within epidermis Hair, sebaceous glands and ducts of sweat glands.

Color of skin depends on : : 

Color of skin depends on : Pigmentation of skin: Melanocytes contain brown pigment called as Melanin which darkens the skin on exposure to sunlight Hb content in blood: The level oxygenation of Hb and amount of blood circulating in dermis play imp. role in skin coloration: # Hb content decreases- Pale skin # Excess decrease in Hb due to Cynosis – bluish skin # When blood rushes to skin due to cutaneous vasodilation –Pink skin Bile pigments in blood and carotenes in subcutaneous fat give the skin a yellowish color .

DERMIS: Connective tissue layer made up of dense & stout collagen fibers, fibroblasts and histocytes.Collagen fibers have elastic property and capable of storing water. The two layers of dermis are : : 

DERMIS: Connective tissue layer made up of dense & stout collagen fibers, fibroblasts and histocytes.Collagen fibers have elastic property and capable of storing water. The two layers of dermis are : 1)Superficial papillary layer # Projects into epidermis # Contain blood vessels, lymphatic, and nerve fibers. # Has some pigment containing cells called CHROMATOPHORE. # Dermal papillae are finger like projections arising from this layer. # Each papilla contain a plexus of capillaries and lymphatics which are oriented perpendicular to the skin surface.The papilla are surrounded by rete ridges extending from the epidermis. 2) Reticular layer : # Made up of reticular and elastic fibers. # These fibers are found around the hair bulbs, sweat glands and sebaceous glands. # This layer also contain mast cells, nerve endings, lymphatics, epidermal appendages and fibroblasts. # The hair follicles with hairs, nails, sweat glands and sebaceous glands, even mammary glands are considered as appendages of the skin.

Certain masses of specialized sensory nerve tissue receptors of dermis are : : 

Certain masses of specialized sensory nerve tissue receptors of dermis are : Ruffini’s corpuscle: Receptor for sensation of heat and continuous pressure. Meissner’s corpuscle: Medium sized, found in skin of mostly of palms and soles. Krause corpuscle: Encapsulated nerve ending in mucous membrane of mouth, eyes, nose and genitals. Pacinian corpuscle: Most complicated nerve ending found throughout body and sensitive to pressure and vibration. * Immediately below the dermis, subcutaneous tissue is present which is a loose connective tissue connecting the skin with internal structures of the body and serving as an insulator to protect the body from excessive heat and cold of environment.

GLANDS OF SKIN: The skin contain 2 types of glands: : 

GLANDS OF SKIN: The skin contain 2 types of glands: Sebaceous glands: These are simple or branched alveolar glands situated in the dermis of skin. # Structure- Ovoid or spherical in shape, developed from hair follicles and covered by connective tissue capsule. # Secretion- Secrete an oily substance called Sebum which is formed by liquefication of the alveolar cells. # Composition- Contain: free fatty acids, sterols, paraffin, waxes, squalene and triglycerides. # Functions- *Free f.a. has antibacterial and antifungal actions. *lipid content keep the skin smooth and oily, also protecting from unnecessary desquamation & injury caused by dryness; also prevent heat loss from body which is imp in cold climate.

Sweat glands : There are 2 types of glands: : 

Sweat glands : There are 2 types of glands: Eccrine glands : # Distribution throughout the body with exterior opening through sweat pore with watery and clear secretion. # It function throughout the life and play imp. role In temp. regulation. # It’s secretion increases during temp. & emotions conditions under nervous control. # Have nerve supply by sympathetic cholinergic fibers. Apocrine glands : # Distribution only in limited areas like axilla, pubis, areola & umbilicus with opening into hair follicle having thick & milky secretion. # It start functioning only in puberty and had no role in temp. regulation. # It’s secretion increases only in emotional conditions under hormonal control. # Have nerve supply by sympathetic adrenergic fibers.

Functions of skin : Skin serves as many functions : : 

Functions of skin : Skin serves as many functions : Protective fxn. – Skin forms the covering of all the organs of the body and gives protection in following ways : Protection from bacteria and toxic substances by secreting lysozyme. Protection from mechanical blow. Protection from UV rays with the help of melanin pigment & increase in thickness of stratum corneum.

Sensory fxn. -Skin is considered as largest sensory organ in body having many nerve endings, which form the specialized cutaneous receptors.Storage fxn. -Skin stores fat, water, chloride & sugar, can also store blood by the dilation of cutaneous blood vessels. Synthetic fxn. -Vitamin D-3 is synthesized in skin by action of UV rays from sunlight on cholesterol.Regulation of body temp. – Excess heat is lost from body through skin by radiation, conduction, convection and evaporation. Sweat glands play active part in heat loss by secreting sweat. The lipid content of sebum prevents heat loss from body in cold climate. : 

Sensory fxn. -Skin is considered as largest sensory organ in body having many nerve endings, which form the specialized cutaneous receptors.Storage fxn. -Skin stores fat, water, chloride & sugar, can also store blood by the dilation of cutaneous blood vessels. Synthetic fxn. -Vitamin D-3 is synthesized in skin by action of UV rays from sunlight on cholesterol.Regulation of body temp. – Excess heat is lost from body through skin by radiation, conduction, convection and evaporation. Sweat glands play active part in heat loss by secreting sweat. The lipid content of sebum prevents heat loss from body in cold climate.

Regulation of water and electrolyte balance - It is done by excreting water and salts through sweat.Excretory fxn. -Skin can excrete small quantities of waste materials like urea, salt & fatty substances.Absorptive fxn. – Skin can absorb the fat soluble substances and some ointments. Secretory fxn. – Skin secretes sweat through sweat glands and sebum through sebaceous glands. By secreting sweat, skin regulates body temp. and water balance. Sebum keeps the body smooth and moist. : 

Regulation of water and electrolyte balance - It is done by excreting water and salts through sweat.Excretory fxn. -Skin can excrete small quantities of waste materials like urea, salt & fatty substances.Absorptive fxn. – Skin can absorb the fat soluble substances and some ointments. Secretory fxn. – Skin secretes sweat through sweat glands and sebum through sebaceous glands. By secreting sweat, skin regulates body temp. and water balance. Sebum keeps the body smooth and moist.

Thanks a lot ! Reena Gill M-pharmacy 1st year ( Pharmaceutics)