Skin and its appendages
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| Keratinocytes | - most common cell type in the epidermis
- arise from deepest layer of epidermis
- present in all epidermal layers
- produce keratin: tough fibrous protein that gives the epidermis its protective properties
- dead at skin's surface
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| Layers of the epidermis (top to bottom) | - stratum corneum
- stratum lucidum (only in thick skin)
- stratum granulosum
- stratum spinosum
- stratum basale
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| Stratum basale | - deepest layer of the epidermis
- single row of stem cells that make up the youngest keratinocytes
- active cell division
- attached to underlying dermis
- rely on capillaries in dermis for nutrients
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| Tactile epithelial cells | - found in stratum basale
- associated with sensory nerve endings
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| Melanocytes | - make melanin and transport it to nearby keratocytes
- respond to UV radiation by increasing production of melanin and transporting to nearby keratocytes--> suntan
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| Melanin | - shields the cell nuclei from incoming UV radiation
- more melanin in each melanocyte --> darker skin
- most abundant skin pigment
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| Stratum spinosum | - several layers of keratinocytes connected by desmosomes
- mitosis occurs, but less than in stratum basale
- relies on capillaries in underlying dermis for nutrients
- thick bundles of intermediate filaments that contain tension resisting pre-keratin
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| Dendritic cells | - found in the stratum spinosum
- part of the immune system
- engulf foreign antigens that invade epidermis
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| Stratum granulosum | - 1-5 layers of flattened keratinocytes
- relies on capillaries in underlying dermis for nourishment
- contains intermediate filaments (pre-keratin)
- keratohyaline granules help form keratin
- lamellated granules contain a waterproofing glycolipid
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| Stratum lucidum (thick skin only) | - few rows of flat, dead keratinocytes
- cells are identical to those in stratum corneum
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| Stratum corneum | - thick layer of dead keratinocytes
- keratinocytes are flat sacs filled with keratin
- protects skin against abrasion and penetration
- intercellular glycolipid keeps layer waterproof
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| submaxillary plexus | - located just below the dermal papillae
- supplies superficial dermal tissue, dermal papillae, and epidermis
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| dermal plexus | - between the hypodermis and dermis
- nourishes the hypodermis and deep dermis
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| papillary layer | - made up of areolar CT proper
- contains dermal papillae
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| dermal papillae | - finger-like projections that interface with overlying epidermis and increase surface area for exchange
- on palms and soles, they lie atop dermal ridges that make epidermal ridges ==> finger prints
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| reticular layer | - 80% of thickness of the dermis
- dense irregular CT
- thick bundles of interlacing collagen and elastic fibers
- separations between collagen bundles form cleavage lines
- extreme stretching can tear the collagen, causing stretch marks
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| flexure lines | - arise from the deep part of the dermis
- result from the repeated folding of the skin
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| hypodermis | - deep to the skin
- also called superficial fascia
- contains areolar and adipose CT
- anchors skin to underlying structures
- helps insulate the body
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| types of skin pigments | - melanin
- carotene
- hemoglobin
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| parts of a nail | - distal free edge
- body
- root
- nail bed: bed of deep epidermis on which nail rests
- nail matrix: thickened proximal end where active nail growth occurs
- lunule
- nail folds
- eponychium
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| hair | - flexible strand of dead, keratinized cells
- root: embedded in the skin
- shaft: projects above skin surface
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| layers of hair | - medulla: central core which consists of large cells and air spaces
- cortex: surrounds the medulla and contains several layers of flattened cells
- cuticle: outermost layer with single layer of cells that overlap
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| Hair papilla | - connective tissue which is a nipple-like bit of the dermis that protrude into each hair bulb
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| hair matrix | - epithelial cells in hair bulb, just above papilla, which proliferate to form the hair shaft
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| Hair follicle | - extend from epidermis into dermis
- associated with arrector pili muscle, which causes hair to stand erect in response to fear, cold, etc.
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| hair cross-sections | round cross-section = straight hair
oval cross-section = wavy hair
flattened cross-section = kinky hair
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| Hair color | - hair pigment made by melanocytes at base of hair follicle; it's transferred into cells of the hair root
- different proportions of 2 types of melanin combine to make the common hair colors
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| hair types | - vellus hairs: fine and short body hairs of women and childen
- terminal hairs: longer and coarser hair of scalp, axillary, and pubic area in adults
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| Sebaceous glands | - occur over whole body except palms & soles
- secrete sebum (oily)
- simple alveolar glands
- holocrine secretion: entire cell breaks up to form secretion
- most associated with hair follicle
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| Sebum | - oily substance
- collects dirt
- softens & lubricates hair and skin
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| Eccrine glands (merocrine) | - most numerous sweat gland
- produce true sweat; present on palms, soles & forehead
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| Sweat | - 99% water with some salts
- contains traces of metabolic wastes
- a blood filtrate
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| Apocrine glands | - large sweat glands confined to axillary, anal, & genital areas
- ducts open into hair follicles
- musky odor
- gland activity increases with sexual foreplay
- signal information about a person's immune system
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| First degree burn | - burn where only the epidermis is damaged
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| second degree burn | - epidermis and upper part of dermis are damaged
- blisters appear with fluid accumulation between epidermal and dermal layers
- skin heals with little or no scarring
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| third degree burn | - damages entire thickness of skin
- burned area appears white, red, or blackened
- skin heals with permanent scarring
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| skin cancer | - basal cell carcinoma: least malignant and most common
- squamous cell carcinoma: arises from keratinocytes of stratum spinosum
- melanoma: cancer of melanocytes; most dangerous type
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| embryonic origins of skin | - epidermis: develops from ectoderm
- dermis and hypodermis: develop from mesoderm
- melanocytes: develop from neural crest cells which are ectoderm in origin
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