Skin and its Appendages
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| The body's largest organ | Skin (Integument)
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| Integumentary system describes what | Skin and its appendages: hair, nails, and skin glands
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| What is skin classified as? | Cutaneous (dry) membrane
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| Two primary layers of skin. | Epidermis and dermis
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| What joins the two layers of skin? | Dermoepidermal junction
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| Hypodermis | Lies beneath dermis (insulation, rich in fat and loose connective tissue
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| Two types of skin | Thick and thin skin
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| Keratinocytes | Consitute more than 90% of cells present; principal structure of the outer skin, sometimes called corneocystes after they are fully hardened (epithethal cells)
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| Melanocytes | Pigment producing cells (5% of total; contribute to skin color and filter ultraviolet light
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| Epidermal dendritic cells | Branched antigen-presenting cells, play a role in immune response; also called Langerhans cells (recognize foreign antigen)
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| Tactile epithelial cells (Merkel cells) | Attach to sensory nerve endings to form "light touch" receptors
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| Dermal papillae | Form ridges
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| Tactile | touch
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| Stratum basale (base layer) | Single layer of columar cells; only these cells undergo mitosis and then migrate through the other layers until they are shed
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| Stratum spinosum (spiny layer) | Cells arranged in 8 to 10 layers with desmosomes that pull cells into spiny shapes; cells rich in RNA (produce keratin)
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| Stratum germinativum | Another name for stratum basale or stratum spinosum and stratum basale together
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| Stratum granulosum (granular layer) | Cells arranged in two to four layers and filles with keratohyalin granules; contains high levels of lysosomal enzymes
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| Stratum lucidum (clear layer) | Cells filled with keratin precursor called eleidin; absent in thin skin
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| Stratum corneum (horny layer) | Most superficial layer, dead cells filled with keratin (barrier area)
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| 35 days | Turnover or regeneration time referred to time required for epidermal cells to form in stratum basale and migrate to the skin surface
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| Epidermal growth factor | Regulates epidermal growth and repair
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| Callus formation | Shortened turnover time will increase the thickness of the stratum corneum
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| Amount of stratum basale cells to enter mitosis daily | 10 to 12%
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| Epidermal proliferating unit | Each group of 8 to 10 basal cells in mitosis with their vertical columns of migrating keratinocytes
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| Dermoepidermal junction | A basement membrane with unique fibrous elements and a polysaccharide gel "glue" the epidermis to the dermis below. The junction is a partial barrier to the passage of some cells and large molecules
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| Dermis | "true skin" gives strength to skin, serves as a reservoir storage area for water and electrolytes, rich vascular supply plays a critical role in temperature regulation
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| Structures in dermis | Arrector pili muscles and hair follicles, sensory receptors, sweat and sebaceous (oil) glands, blood vessels
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| Papillary layer | composed of dermal papillae that project into the epidermis; contains fine collagenous and elastic fibers and the demoepidermal junction; forms unique pattern that gives individual fingerprints
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| Reticular layer | contains dense, interlacing white collagenous fibers and elastic fibers to make the skin tough yet stretchable; when processes from animal skin, produces leather
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| Layers of dermis | Papillary layer
Reticular layer
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| The dermis does not | continually shed and regenerate itself as does the epidermis
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| During dermis wound healing | fibroblasts begin forming and unusually dense mass of new connective fibers; if not replaced by normal tissue, this mass remains a scar
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| Cleavage lines | patterns formed by the collagenous fibers of the reticular layer of dermis; aka Langer's lines (incision lines)
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| Hypodermis | aka subcautaneous layer or superficial fascia (connective tissue) located deep to the dermis; forms connection between skin and other structures; not part of the skin
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| Melanin | (in epidermis)basic determinant is quantity, type, and distribution of melanin (color/pigment of the skin)
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| Types of melanin | Eumelanin and Pheomelanin
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| Eumelanin | group of dark brown, almost black, melanins
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| Pheomelanin | group of reddish and orange melanins
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| Melanosomes | Packets of melanin released by melanocytes
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| Melanosomes are ingested by | surronding keratinocytes and form a cap over the nucleus (protect from UV rays)
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| Albinism | congenital absence of melanin
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| Age spots | Cumulative effects of UV ray exposure
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| Skin color | how much melanin you produce (more sun=more melanin (tan))
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| Beta-carotene | (makes vitamin A) group of yellowish pigments from food can also contribute to skin color
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| Hemoglobin | color changes occur as a result of changes in blood flow
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| Redder skin | blood flow increase to the skin (dilate blood vessels)
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| Cyanosis | Bluish color caused by darkening of hemoglobin when it loses oxygen and gains carbon dioxide
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| Bruising | can cause a rainbow of colors to the skin
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| Functions of the skin Protection | Physical barrier to microorganisms, barrier to chemical hazards, reduces potential for mechanical trauma, prevents dehydration, protects from excess UV ray exposure
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| Emulsified protective barrier | formed by mixing of residue and secretions of sweat and sebacaous glands with sloughed epithelial cells from skin surface
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| Desquamation | shedding of epithelial elements (removing layers)
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| Functions of surface film | Antibacterial, anti-fungal activity, lubrication, hydration of skin surface, buffer of caustic irritants, blockade of toxic agents
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| Chemical composition from epithelial elements | amino acids, sterols and complex phospholipids (cell membrane)
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| Chemical composition from sebum | Fatty acids, triglycerides, and waxes
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| Chemical composition from sweat | water, ammonia, urea, and lactic and uric acid (kill bacteria)
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| Sensation of the skin | Skin acts as a sophisticated sense organ. Somatic sensory receptors detect stimuli that detection of pressure, touch, temperature, pain, and other general senses
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| Flexibility of the skin | skin is supple and elastic, thus permitting change in body contours without injury
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| Immunity of skin | Phagocytic cells destroy bacteria. Epidermal dendritic cells trigger helpful immune reaction working with helper T cells
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| Homeostasis of body temperature | To maintain homeostasis of body temperature, heat production must equal heat loss; skin plays a critical role in this process
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| Heat production | by metabolism of foods in skeletal muscles and liver. (more physical energy used=more heat the body produces)
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| Skin excretion | Water, Urea/ammonia/uric acid
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| Vitamin D production | started in the skin(exposure to UV light), blood transports precursor to liver and kidneys
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| Heat loss | approximately 80% of heat loss occurs through the skin
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| Evaporation | to evaporate any fluid, heat energy must be expended, this method is important when temperatures are high and its the only method heat can be lost from skin (sweating)
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| Radiation | transfer of heat from one object to another without actual contact; important method of heat loss in cool environment (no contact)
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| Conduction | transfer of heat to any substance in contact with the body; accounts for relatively small amounts of heat loss (contact)
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| Convection | transfer of heat away from a surface by movement of air; usually accounts for a small amount of heat loss (air movement)
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| Heat loss by the skin is controlled by | Negative feedback loop
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| Monitor the body's internal temperature | Receptors in the hypothalamus
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| Development of hair | hair follicles and hair develop from epidermis; mitosis of cells of germinal matrix forms hairs
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| Lanugo | fine and soft hair present before birth
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| Terminal hair | coarse pubic and axillary hair that develops at puberty
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| Papilla | cluster of capillaries under germinal matrix
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| Root | part of hair embedded in follicle in dermis
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| Shaft | visible part of hair (dead)
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| Medulla | inner core of hair (meat)
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| cortex | outer portion
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| Color of hair | result of different amounts, distribution, types of melanin in cortex of hair
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| Growth | growth and rest periods alternate; hair on head averages 5 inches of growth per year
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| Sebum | Skin oil
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| Male pattern baldness (androgenic alopecia) | results from combination of genetic tendency and male sex hormones
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| Two types of sweat glands | eccrine and apocrine
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| Eccrine glands | most numerous, quite small, simple, coiled, tubular,function throughout life, secrete perspiration or sweat, eliminates wastes and help maintain a constant core temperature
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| Apocrine glands | deep, limited distribution (axilla, areola of breast, anus), large, simple, branched, tubular, function begins at puberty, secretion shows cyclic changes in female with menstrual cycle
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| Nails | consist of epidermal cells converted to hard keratin
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| Nail body | visible part of each nail
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| Root | part of nail in groove hidden by fold of skin, the cuticle
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| Lunula | moon-shaped white area nearest root
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| Nail bed | layer of epithelium under nail body, contains abundant blood vessels
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| Onycholysis | separation of a nail from the nail bed
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| Nail growth | nails grow by mitosis of cells in stratum basale beneath lunula
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| Sebaceous glands | secrete sebum, lipid components have anti-fungal activity, simple, branched, in dermis expect for soles and palms, secretion increases in adolescence (may lead to pimples)
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| Ceruminous glands | Modified apocrine sweat glands, simple, coiled, tubular, empty contents into external ear, protect area, excess can cause blockage of ear canal
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| Cerumen (wax) | mixed secretions of sebaceous and ceruminous glands
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| Epidermis | superficial, thinner layer (epithelial layer)
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| Dermis | the deep, thicker layer (dense and vascular connective tissue)
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| Friction ridges | form fingerprints or footprints, underlying dermal papillae are raised in curving parallel ridges
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| Keratinocytes | principal structure element of the outer skin (skin cells that become filled with keratin)
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| Strata | layer
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| Keratin | tough, fibrous protein
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| Corneocytes | after dead and fully keratinized, flattened keratinocytes
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| Melanocytes | contribute colored pigments to the skin and serve to decrease amount of UV light
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| Dendritic cells (DCs) (Langerhans cells) | branched cells that play a role in immunity
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