Which is the largest organ in our body

Which is the largest organ in our body ?

What is Skin ?

Skin is the outermost covering and largest organ of the body. It is not uniformly thick.

SKIN Thick skin Thin skin ØPresent in–Sole & Palm ØPresent in all other parts of ØContain no hair & Sebaceous gland the body Ø Contain hair & Sebaceous gland

HISTOLOGY Skin Made Up Of 3 Layers 1. Superficial -- Epidermis 2. Deep -- Dermis 3. Deeper -- Sub cutaneous tissue

EPIDERMIS No blood vessels; nutrition by diffusion through capillaries of dermis Consists of 5 layers : From superficial to deep they are; 1. Stratum Corneum 2. Stratum Lucidum 3. Stratum Granulosum 4. Stratum Spinosum (also called prickle cell layer) 5. Stratum Germinatum (also called basal layer) is the deepest layer of epidermis

STRATUM CORNEUM It is the outermost layer Cells are thick Opaque Keratinized No nucleus Keratin is resistant to many form of injury of skin

STRATUM LUCIDUM Present only in thick skin Cells are transparent Melanin granules liquefied to become eledin (precursor of keratin) Hence cell cytoplasm is more transparent (hence the name lucidum)

STRATUM GRANULOSUM Made up of flat polyhedral cells of 3 -4 layers Melanin is injected into this layer from S. Germinatum Synthesis Kerato-hyaline granules from melanin Cells contain large number of these granules (hence called S. granulosum)

STRATUM GERMINATUM Made up of single layer of columnar cells By active mitosis & modification (by way of changing shape & accumulation of granules-keratin) –gives rise other layers Also contain melanocytes (which synthesis melanin and inject to other layers)

THIN SKIN, HAIRY 100 x

THIN SKIN

THICK SKIN

MELANIN Is colored pigment produced by melanocytes(Stratum Germinatum & Stratum Spinosum) Synthesis from Tyrosine

DERMIS Made up of two layers 1. Superficial Papillary layer : Contain collagen & elastic fibers This layer project into the epidermis and gives the appearance of papillae. It contains blood vessels, lymphatics and nerve fibers 2. Deeper Reticular layer : Contain –loose areolar connective tissue & fat (adipose tissue) Also present Fibroblast cells & reticulo-endothelial cells. Blood supply by hair-pin like loop of cutaneous capillaries

Frolich, Human Anatomy, Skin DERMIS—CONNECTIVE TISSUE SUBSTRATE

APPENDAGES OF SKIN 1. 2. 3. 4. 5. Nails(dead tissue of epidermis in certain areas) Hairs Sweat glands Sebaceous glands Mammary glands

COLOR OF THE SKIN Amount of melanin present in the skin The state of circulation in the dermis The amount of reduce Hemoglobin present in the circulation

FUNCTION OF SKIN 1. Protective function : Protection from bacteria and toxic substances Protection from mechanical blow Protection from ultraviolet 2. Sensory function : Largest sense organ with abundant nerve supply, touch, pressure, pain, temperature sensation coetaneous sensation 3. Storage functions : fat, water, chloride, sugar, blood. 4. Synthetic function : Vitamin D 3 is synthesized skin by the action of UV rays on cholesterol.

5. Regulation of water and electrolyte balances. 6. Excretory function. 7. Regulation of body temperature. 8. Secretary function.