The integumentary system Skin characteristics o SA 1 2 2 2 meters squared o Weight 4 5 kg o Is about 7 of total body weight o Functions protection fight bacteria prevents water heat loss o Two distinct regions of the skin Epidermis epithelial cells Dermis underlies the epidermis Makes up most skin Only layer that vascularized fibrous CT Nutrients flow through tissue fluid to dermis o Hypodermis subcutaneous layer deep to the skin Not actually part of the skin but has similar characteristics Also called superficial fascia It is mostly adipose tissue Functions Storing fat hypodermis thickens with weight gain Loosely anchors skin to underlying muscles but still lets skin slide Skin layers o Epidermis from deep to superficial Stratum basale cells are actively mitotic stem cells some newly formed cells become part of the more superficial layers Deepest layer 10 25 of its cells are melanocytes Attached to the dermis also called stratum germinativum because of the rapid cell division that occurs here Stratum spinosum cells contain thick bundles of intermediate filaments made of pre keratin Thick layers Contains lagerhans cells and makes keratinocytes rougher Stratum granulosum cells are flattened organelles deteriorating cytoplasm full of granules and keratinocytes Helps to form keratin in the upper layers Stratum lucidem Layer is thin and translucent Only present in thick skin has just a few layers of few keratinoctyes Stratum corneum cells are dead flat membranous sacs filled with keratin glycolipids in extracellular space 20 30 cell layers thick Accounts for 75 of epidermal thickness o Dermis strong CT with blood vessels nerve fibers and lymphatic vessels major hair Most of our protection Outermost layer follicles in the dermis Papillary layer Reticular layer Superficial Aerolar CT Loose intertwinement of CT elastic fibers and collagen This looseness allows phagocytes to move freely Its superior layer indents the epidermis Dermal papillae have capillaries and nerve endings to exchange with epidermis and provide deep receptors Deep to papillary layer Account for 80 of the thickness of the dermis Made of dense fibrous CT ass oppose to loose Has collagen fibers running parallel to the skin surface these are called Gives supporting strength to the skin When an incision is made parallel to the tension lines the skin heals tension lines faster o Hypodermis o Thus medical incisions are made this way Epidermis is keratinized stratified squamous epithelium consisting of four cell types and four or five layers Cells of the epidermis o Keratinocytes produce keratin gives epidermis its protective ability Most abundant of the epidermis cells Arise from stratum basale deepest layer These cells are constantly undergoing mitosis and sre pushed up the layers As the keratinocytes reach the surface they are dead We have a completely new epidermis every 25 45 days Friction increases proliferation Hands feet have increased keratin production o Melanocytes produce melanin Synthesized deep in the epidermis and as they rise some of them combine with keratinocytes to fight UV light o Tactile merkel cells sensory receptors for touch Associated with a nerve ending to serve as the receptor o Langerhan cells phagocyte antigen presenting cells Arise from bone marrow to the epidermis Serve as phagocytes to fight foreign bodies and antigens Skin color o Determined by melanin keratin and hemoglobin o Melanin is made of tyrosine AA ranges in color synthesis depends on tyrosinase individual differences in skin color reflect kind of melanin made and retained not number of melanocytes Freckles and pigmented moles are local accumulations of melanin o Melanocytes are stimulated to a greater activity when we expose our skin to sunlight to help protect the DNA oof our skin cells from UV radiation Excessive sun exposure causes clumping of elastic fibers which can result in leathery skin depress the immune system and alter the DNA of skin cells lead to skin cancer o Carotene yellow orange pigment found in plant products tends to accumulate in stratum corneum and in fatty tissue of hypodermis o Hemoglobin causes pinkish hue of fair skin Functions of the integumentary system o Protection Chemical barriers Physical mechanical barriers Biological barriers o Body temperature regulation o Cutaneous sensation o Metabolic function o Blood reservoir o Excretion Skin temperature regulation o Cold vasoconstriction o Heat vasodilation Burn Brings blood to the skin for heat exchange with the environment You don t actually loose heat until sweat has been evaporated o Metabolism effects Cholesterol molecules in the skin can serve to synthesize vitamin D from the sunlight o Tissue damage inflected by intense heat electricity radiation or certain chemicals denatures cell proteins and causes cell death in the affected area o Immediate threat is due to loss of body fluids with proteins and electrolytes dehydration electrolyte imbalance leading to renal shutdown and circulatory shock o After initial threat of dehydration has been accounted for threat shifts to infection o Burned skin is sterile for about 24 hours after 24 hours bacteria fungi and other pathogens can easily enter the body o 1st degree burns damage only to the epidermis o 2nd degree damage to the epidermis and upper layer of dermis o 3rd degree damage to the entire sin causing full thickness burns o Initially no nerve endings have been destroyed therefore initially no pain in the area skin regeneration can eventually occur but cannot wait due to fluid loss and infection therefore grafts are usually necessary o Skin grafts First burned skin must be debrided removed Area is then flooded with antibiotics and covered with synthetic membrane Then healthy skin is transplanted to the burn site Scar tissue often forms o Burns are critical if Over 25 of the body has 2nd degree burns Over 1 of the body has 3rd degree burns There are 3rd degree burns to the face hand or feet possibility of burned respiratory pathways or immobilization of joints The immune system Functional system made up of two intrinsic defense systems that act independently and cooperatively to provide resistance to disease o Innate nonspecific defense system immediate response 1st and 2nd line of defense respond within minutes 1st external membrane skin mucosa 2nd takes effect when first has been penetrated inflammation proteins phagocytes o Adapted specific defense system 3rd line of defense Attacks foreign substances
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