Part 2 Integumentary System Two Divisions of the Integumentary System 1 Skin integument cutaneous membrane 09 29 2010 o Skins 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 dermis Composed of the superficial epidermis and the deeper 2 Accessory skin structures skin appendages o i Sweat Sudoriferous glands o ii Sebaceous oil glands o iii Hair hair follicles o iv 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 Stratum Basale cells The deepest stratum A single layer of cells including keratinocytes melanocytes Merkel o Keratinocytes are mitotically active producing cells for the superficial layers hence the stratum basale is also known as the stratum germinativum Melanocytes produce the pigment melanin contained in melanosomes melanosomes accumulate on the superficial surface of the keratonocytes in the stratum basale melanin acts as a chemical shield to protect the nuclei of the keratinocytes from the harmful effects of UV radiation in sunlight melanin gives skin its color albinism genetic condition in which melanin is not synthesized When you go out into the sun these cells make extra melanin to protect you from getting burned by the sun s ultraviolet or UV rays tanning Merkel cells at the epidermal dermal junction associate with free nerve endings to form Merkel Discs which act as touch receptors Stratum Spinosum Several layers of cells Cells are connected by desmosomes hold cells together which cause the cells to appear spiny during histological preparation Cells contain intermediate filaments called tonofilaments Epidermal dendritic cells Langerhans cells in the stratum spinosum act as macrophages to engulf and digest pathogens Stratum Granulosum Composed of 3 5 layers of cells Cells contain two types of granules o Lamellated granules contain glycolipids the lipids that make the epidermis water proof o Keratohyaline granules contain the tough insoluble protein keratin which makes the epidermis tough and abrasive resistant Stratum Lucidum Thin translucent layer of deal cells Thickens the epidermis Present only in thick skins palms soles Stratum Corneum Superficial layer of the epidermis Composed of 20 30 layers of dead flat cells Deal cells are impregnated with glycolipids and keratin to provide a tough durable water proof coat Replaced every 3 4 weeks The Dermis layer Consists of the superficial papillary layer and the deep reticular The papillary layer Composed of areolar connective tissue 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 increased friction and enhance gripping Pattern of epidermal ridges is genetically determined and therefore unique to an indivudual acts a the basis for finger printing Reticular Layer of the Dermis Deeper layer accounting for 80 of the dermis Composed of dense irregular connect tissue Contains the touch receptors for deep pressure called Pacinian Cleavage tension lines areas of the reticular layer with less Incisions made parallel to the cleavage lines gape less and Striae stretch marks indicate dermal tearing replaced by slivery corpuscles collagen bundles therefore heal faster white scars Location of the Nervous Structures in the 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 is 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 the epidermis but reside in the dermis o Sweat Sudoriferous glands o Sebaceous oil glands o Hairs hair follicles o Nail Sweat Glands Suderiferous glands Simple coiled tubular multicellular exocrine glands Two types Eccrine and Apocrine Eccrine Sweat Glands o Three million per person o Abundant in the palms soles and forehead o Secrete sweat o Use the merocrine mode of secretion o Hence the eccrine sweat glands are also known as merocrine sweat glands Composition of Sweat Hypotonic filtrate of blood 99 water Antibodies Vitamic 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 Apocrine Sweat Glands 2000 of them located in the anogenital and axillary armpits areas Become active after puberty when they are stimulated by the sex steroid hormones Secrete a viscous yellowish fluid onto hair follicles Secrete their product via merocrine mode of secretion Secretion is associated with body odor hence the apocrine sweat glands are also known as odoriferous glands Two 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 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 Blackheads popped whiteheads that result in oxidation and glands darkening Acne inflammation of sebaceous glands caused by bacteria Hairs Pili Produced by cells in the matrix inside hair follicles Each hair has two regions shaft and root Shaft region exposed above the skin Root region below the skin enclosed by the hair follicle Three Concentric Layers of Hair Hair is composed of three concentric layers of keratinized cells o Inner medulla the core o Middle cortex the largest layer o Outer cuticle a single layer of overlapping cells that protects the underlying layers and to prevent hair from matting Conditioners
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