Integumentary System - Skin(Integumentary System considered...

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Human Anatomy & Physiology: Integumentary System, Lecture Notes, Ziser, 2005 1 Skin ( Integumentary System) considered an organ or an organ system body’s largest organ organ of greatest surface area:15-20 sq ft. (1.5-2 m 2 ) General Functions: 1. protection mechanical chemical bacterial UV desiccation 2. temperature homeostasis >temp sweat glands, flushing <temp arrector pili, pale 3. excretion affects fluid & electrolyte balance sweat glands release: water, salts, ammonia oil glands release: lipids, acids 4. sensation touch (light touch, wind, etc) pressure heat cold pain 5. synthesis vitamin D precursor passes through capillaries in skin and light converts it to vitamin D 6. nonverbal communication eg. humans and other primates have much more expressive faces than other animals Layers of Skin: epidermis dermis hypoderms
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Human Anatomy & Physiology: Integumentary System, Lecture Notes, Ziser, 2005 2 Epidermis stratified squamous epithelium upper layers d ead, filled with keratin (waxy protein) lower layers living cells replaced every 35-45 days subdivided into 5 identifiable layers: a. stratum basale lowermost layer of epidermis single cell l ayer thick only cells that get ad equate nutrition and oxygen by diffusion from tissues below actively dividing cells bordered below by basement membr ane b. stratum spinosum several layers thick less mitosis flattened, irregular, spinelike projections [ basale + spinosum = stratum germinativum growing layers] c. stratum granulosum very thin; 2-3 cell layers thick as cells move up from s. basale they die & get flatter and thinner keratinization begins here d. stratum lucidum thin translucent band only found in thick areas of epidermis: soles of feet palms of hand e. stratum corneum thickest of all layers; 3/4 th ‘s the thickness of epidermis 20-30 cell layers thick dead cells completely filled with keratin water resistant main protection against biologi cal and chemical assault takes keratinocytes 30-40 days from their formation in s basale until they flake off of the s corneum cells of epidermis:
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Human Anatomy & Physiology: Integumentary System, Lecture Notes, Ziser, 2005 3 1. stem cells undifferentiated cells found only in deepest layer 2. keratinocytes most cells in epidermis synthesize keratin 3. melanocytes also in deepest layer synthesize pigment melanin 4. Merkel cells touch receptors, attached to nerve cell 5. dentritic cells ( Langerhans cells) found in s spinosum and s granulosum are macrophages that stand guard against toxins, microbes and other pathogens that penetrate the skin if detected they alert immune system Dermis (=hide) strong, flexible, connective tissue gives skin its strength and resilience gel-like ma trix contains collagen, elastic and reticular fibers rich in nerves, r eceptors, blood vessels, lymph vessels hair follicles and sweat glands extend into it two layers: a. papillary layer mainly areolar connective tissue lots of blood vessels dermal papillae capillary loops sensory cells produce finger prints b. reticular layer
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