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Chapter 6

Skin and its Appendages

The body's largest organ Skin (Integument)
Integumentary system describes what Skin and its appendages: hair, nails, and skin glands
What is skin classified as? Cutaneous (dry) membrane
Two primary layers of skin. Epidermis and dermis
What joins the two layers of skin? Dermoepidermal junction
Hypodermis Lies beneath dermis (insulation, rich in fat and loose connective tissue
Two types of skin Thick and thin skin
Keratinocytes Consitute more than 90% of cells present; principal structure of the outer skin, sometimes called corneocystes after they are fully hardened (epithethal cells)
Melanocytes Pigment producing cells (5% of total; contribute to skin color and filter ultraviolet light
Epidermal dendritic cells Branched antigen-presenting cells, play a role in immune response; also called Langerhans cells (recognize foreign antigen)
Tactile epithelial cells (Merkel cells) Attach to sensory nerve endings to form "light touch" receptors
Dermal papillae Form ridges
Tactile touch
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
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)
Stratum germinativum Another name for stratum basale or stratum spinosum and stratum basale together
Stratum granulosum (granular layer) Cells arranged in two to four layers and filles with keratohyalin granules; contains high levels of lysosomal enzymes
Stratum lucidum (clear layer) Cells filled with keratin precursor called eleidin; absent in thin skin
Stratum corneum (horny layer) Most superficial layer, dead cells filled with keratin (barrier area)
35 days Turnover or regeneration time referred to time required for epidermal cells to form in stratum basale and migrate to the skin surface
Epidermal growth factor Regulates epidermal growth and repair
Callus formation Shortened turnover time will increase the thickness of the stratum corneum
Amount of stratum basale cells to enter mitosis daily 10 to 12%
Epidermal proliferating unit Each group of 8 to 10 basal cells in mitosis with their vertical columns of migrating keratinocytes
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
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
Structures in dermis Arrector pili muscles and hair follicles, sensory receptors, sweat and sebaceous (oil) glands, blood vessels
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
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
Layers of dermis Papillary layer Reticular layer
The dermis does not continually shed and regenerate itself as does the epidermis
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
Cleavage lines patterns formed by the collagenous fibers of the reticular layer of dermis; aka Langer's lines (incision lines)
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
Melanin (in epidermis)basic determinant is quantity, type, and distribution of melanin (color/pigment of the skin)
Types of melanin Eumelanin and Pheomelanin
Eumelanin group of dark brown, almost black, melanins
Pheomelanin group of reddish and orange melanins
Melanosomes Packets of melanin released by melanocytes
Melanosomes are ingested by surronding keratinocytes and form a cap over the nucleus (protect from UV rays)
Albinism congenital absence of melanin
Age spots Cumulative effects of UV ray exposure
Skin color how much melanin you produce (more sun=more melanin (tan))
Beta-carotene (makes vitamin A) group of yellowish pigments from food can also contribute to skin color
Hemoglobin color changes occur as a result of changes in blood flow
Redder skin blood flow increase to the skin (dilate blood vessels)
Cyanosis Bluish color caused by darkening of hemoglobin when it loses oxygen and gains carbon dioxide
Bruising can cause a rainbow of colors to the skin
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
Emulsified protective barrier formed by mixing of residue and secretions of sweat and sebacaous glands with sloughed epithelial cells from skin surface
Desquamation shedding of epithelial elements (removing layers)
Functions of surface film Antibacterial, anti-fungal activity, lubrication, hydration of skin surface, buffer of caustic irritants, blockade of toxic agents
Chemical composition from epithelial elements amino acids, sterols and complex phospholipids (cell membrane)
Chemical composition from sebum Fatty acids, triglycerides, and waxes
Chemical composition from sweat water, ammonia, urea, and lactic and uric acid (kill bacteria)
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
Flexibility of the skin skin is supple and elastic, thus permitting change in body contours without injury
Immunity of skin Phagocytic cells destroy bacteria. Epidermal dendritic cells trigger helpful immune reaction working with helper T cells
Homeostasis of body temperature To maintain homeostasis of body temperature, heat production must equal heat loss; skin plays a critical role in this process
Heat production by metabolism of foods in skeletal muscles and liver. (more physical energy used=more heat the body produces)
Skin excretion Water, Urea/ammonia/uric acid
Vitamin D production started in the skin(exposure to UV light), blood transports precursor to liver and kidneys
Heat loss approximately 80% of heat loss occurs through the skin
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)
Radiation transfer of heat from one object to another without actual contact; important method of heat loss in cool environment (no contact)
Conduction transfer of heat to any substance in contact with the body; accounts for relatively small amounts of heat loss (contact)
Convection transfer of heat away from a surface by movement of air; usually accounts for a small amount of heat loss (air movement)
Heat loss by the skin is controlled by Negative feedback loop
Monitor the body's internal temperature Receptors in the hypothalamus
Development of hair hair follicles and hair develop from epidermis; mitosis of cells of germinal matrix forms hairs
Lanugo fine and soft hair present before birth
Terminal hair coarse pubic and axillary hair that develops at puberty
Papilla cluster of capillaries under germinal matrix
Root part of hair embedded in follicle in dermis
Shaft visible part of hair (dead)
Medulla inner core of hair (meat)
cortex outer portion
Color of hair result of different amounts, distribution, types of melanin in cortex of hair
Growth growth and rest periods alternate; hair on head averages 5 inches of growth per year
Sebum Skin oil
Male pattern baldness (androgenic alopecia) results from combination of genetic tendency and male sex hormones
Two types of sweat glands eccrine and apocrine
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
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
Nails consist of epidermal cells converted to hard keratin
Nail body visible part of each nail
Root part of nail in groove hidden by fold of skin, the cuticle
Lunula moon-shaped white area nearest root
Nail bed layer of epithelium under nail body, contains abundant blood vessels
Onycholysis separation of a nail from the nail bed
Nail growth nails grow by mitosis of cells in stratum basale beneath lunula
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)
Ceruminous glands Modified apocrine sweat glands, simple, coiled, tubular, empty contents into external ear, protect area, excess can cause blockage of ear canal
Cerumen (wax) mixed secretions of sebaceous and ceruminous glands
Epidermis superficial, thinner layer (epithelial layer)
Dermis the deep, thicker layer (dense and vascular connective tissue)
Friction ridges form fingerprints or footprints, underlying dermal papillae are raised in curving parallel ridges
Keratinocytes principal structure element of the outer skin (skin cells that become filled with keratin)
Strata layer
Keratin tough, fibrous protein
Corneocytes after dead and fully keratinized, flattened keratinocytes
Melanocytes contribute colored pigments to the skin and serve to decrease amount of UV light
Dendritic cells (DCs) (Langerhans cells) branched cells that play a role in immunity
Created by: 500302924
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