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Chapter 6
Skin and its Appendages
| Question/Term | Answer |
|---|---|
| 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 |
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