Skin is the largest organ of the body surface area of 1 2 to 2 2 square meters weighs 9 to 11 pounds 4 5kg 7 of the total body weight Composed of the superficial EPIDERMIS and the deeper DERMIS Integumentary System 2 Divisions 1 Skin integument Cutaneous membrane 2 Accessory skin structures skin appendages Sweat sudoriferous glands Sebaceous oil glands Hair hair follicles Nails Strata of the Epidermis Stratum Basale deepest stratum Stratum Spinosum contains tonofilaments Stratum Granulosum contains granules Stratum Lucidum present only in thick skin Stratum Corneum superficial stratum see chart for details The Dermis Consists of the superficial PAPILLARY layer and the deep RETICULAR layer The papillary Layer Composed of areolar CT Surface has peg like projections called DERMAL PAPILLAE house blood capillaries and nerve endings and Meissner s corpuscles which act as touch receptors In thick skin the surface of the papillae are supported by mounds called Dermal Ridges which form impressions on the epidermal surface called the EPIDERMAL RIDGES friction ridges increase friction and enhance gripping Pattern of epidermal ridges is genetically determined and therefore unique to an individual acts as the basis for finger printing Reticular Layer Deeper layer accounting for 80 of the dermis Composed of dense irregular CT Contains the touch receptors for deep pressure called Pacinian corpuscles Cleavage tension lines areas of the reticular layer with less collagen bundles Incisions made parallel to the cleavage lines gape less and therefore heal faster Striae stretch marks indicate dermal tearing replaced by slivery white scars Location of Nervous Structures in Skin Merkel discs epidermal dermal junctions act as light touch Meissner s Corpuscles Papillary layer of the dermis act as touch receptors Root hair plexus wrapped around the base of a hair follicle called the hair bulb and it s stimulated when the hairs bend act as touch Pacinian Corpuscles located in the reticular layer of the dermis and they respond to deep pressure placed on the skin Accessory Structures of the Skin all derived from epidermis but are located in the dermis Sweat Glands simple coiled tubular multicellular exocrine glands Eccrine Apocrine Composition of sweat 3 million person palms soles forehead secrete sweat via MEROCRINE mode of secretion 2000 located in the anogenital and armpit areas secrete viscous yellowish fluid onto hair follicles via MEROCRINE mode of secretion active after puberty when stimulated by the sex steroid hormones secretion is associated with body odor Hypotonic filtrate of blood 99 water Antibodies Vitamin C Salts NaCl Metabolic wastes Dermicidin antimicrobial protein pH between 4 6 Acidic ACIDIC MANTLE acidic pH of sweat prevents microbial growth on the surface of the skin 2 Specialized Sweat Glands Ceruminous glands specialized sweat glands located in the lining of the external ear canal they secrete a bitter substance called CERUMEN earwax which prevents entry of foreign objects such as insects and water into the ear Mammary glands specialized sweat glands located in breasts secrete milk to feed the young Sebaceous Glands Also known as Oil glands Simple alveolar glands Found all over the body except the palms soles Secrete an oily substance called SEBUM into hair follicles and via pores to the surface of the skin Sebum softens and lubricates hair and skin Secrete via the HOLOCRINE mode of secretion Whiteheads sebum accumulated in the ducts of the sebaceous glands Blackheads popped whiteheads that result in oxidation and darkening Acne inflammation of sebaceous glands caused by bacteria Hairs hair Follicles Hairs Pili produced by cells in the MATRIX inside hair follicles each hair has 2 regions Shaft exposed above skin Root below skin enclosed by the hair follicle 3 Concentric Layers of Hair Hair is composed of 3 concentric layers of keratinized cells Inner medulla the core Middle cortex the largest layer Outer cuticle a single layer of overlapping cells that protects the underlying layers and to prevent hair from matting Functions Conditioners keep the cuticle smooth to prevent matting of the hair and split ends Alopecia rate of hair loss outpaces rate of hair growth For protection hair on scalp eyelashes To provide insulation in cold weather bands of smooth muscle attached to the hair follicles called the arrector pili muscles contract pulling the hair follicles and hairs from an oblique position to an upright position resulting in dimpling of the skin referred to as goose bumps in this position a layer of air can be trapped on the surface of skin to act as an insulator to prevent heat loss from the body Basal Cell Carcinoma involves the proliferation of stratum basal basale cells The least malignant and most common type of skin cancer 80 grows slowly Squamous Cell Carcinoma involves the cells in the stratum spinosum Second most common type of skin cancer grows rapidly Melanoma proliferation of the melanocytes most aggressive type of skin cancer highly metastatic and resistant to chemotherapy least common Tissue damage by intense heat radiation electricity and chemicals such as acids Classified based on severity First degree burns damage is confined to only the epidermis associated with redness swelling and pain heal in 3 days without medical intervention Ex Sunburn Second degree burns damage to the entire epidermis and the papillary layer of the dermis associated with blisters fluid collection at the epidermal dermal junction swelling redness and pain heal in 3 4 weeks if infection is prevented Third degree burns damage to the entire skin damage to the entire epidermis and dermis including all nerve endings hence the burn site is not painful subjected to infections and fluid loss medical intervention involving grafting fluid protein and ion replacement are required for healing How Do Wrinkles Form loss of elasticity thinning skin lack of moisture When skin is young thick and full of elasticity it can resist muscle tension and does not develop a grove or crease when a facial muscle is contracted such as a frown squint or a smile However as we age and our skin becomes thinner drier less resilient it starts to adhere itself to the underlying muscle tissue So now when we frown the skin gets pulled along with the muscle creating a valley a line or a deep wrinkle over time Botox blocks the transmission of signals from nerves to the muscles by hindering the production of the neurotransmitter
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