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48 Cards in this Set
- Front
- Back
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functions of skin
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- resistance to abrasion
- resistance to infections - prevention of dehydration - protection of underlying tissue from UV light - synthesis of Vitamin D - thermoregulation - excretion - sensation |
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thick skin
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- present only on the palms of the hands and soles of feet
- no hair - keratinized layer in stratum corneum |
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thin skin
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- present everywhere that thick skin is not present
- shows regional variation in amount of hair, number and size of glands, degree of pigmentation, etc. |
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major function of keratinocytes
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- to provide a strongly reinforced epithelium that resists mechanical abrasion
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keratinocytes
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- main component of stratified squamous epithelium of epidermis
- very high keratin content -rich in cysteine, lysine, and histidine --> involved in cross links |
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stratum basale (stratum germinativum)
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- youngest keratinocytes
- single layer of cuboidal or columnar cells lying on the basal lamina - cells are attached to each other by desmosomes and to the basal lamina by hemidesmosomes |
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pemphigus vulgaris
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autoimmune reaction against desmosomes in stratum basale
--> severe blistering |
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bullous pemphigoid
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- autoimmune reaction against hemidesmosomes in the stratum basale
--> severe blistering |
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stratum spinosum
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- cells from stratum basale migrate upward and differentiate into keratinocytes called prickle cells
- vitamin D is synthesized in plasma membranes of stratum spinosum keratinocytes in response to UV light |
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prickle cells
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- form large numbers of desmosomes with adjacent cells
- reinforced internally by prominent bundles of tonofibrils ---> made up of keratin filaments - post mortem shrinkage of cell cytoplasm gives rise to prickly appearance |
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stratum granulosum
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- one to a few cells thick
- keratohyalin granules - lamellar bodies |
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keratohyalin granules
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- flattened cells
- basophilic granules that contain filaggrin - granules content promotes cross link keratin filaments within the cytoplasm |
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filaggrin
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- protein rich in histidine and cysteine
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lamellar bodies
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- membrane-coating granules
- membrane bound vesicles - contain glycolipid, acylceramide - lipids are secreted into the space between granulosum and corneum --> forms waterproof barrier - only hydrophobic molecules can penetrate barrier |
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which cancers do keratinocytes give rise to?
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basal cell and squamous cell carcinoma
--> vulnerability to UV damage |
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stratum Malpighi
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stratum basale, stratum spinosum, stratm granulosum
-- living cell layers |
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stratum lucidum
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- not very visible
- usually seen in thick skin - cells die and lose nuclei |
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stratum corneum
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- layer of skin in contact with the air
- have lost all organelles - layer of dead cells containing cross-linked soft keratin - attached to each other by desmosomes |
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normal turnover of keratinocytes
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30 days
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melanocytes
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- source of skin pigment
- present in basale cell layer - synthesize melanin - originate in neural crest and migrate to the skin during development |
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melanin
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- synthesized in melanocytes
- exported to keratinocytes (cytocrine secretion) --> expresses melanin - shield dividing cells from damaging UV |
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albinism
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absence of melanin
- due to lack of or defeat in tyrosinase enzyme required to synthesize melanin |
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vitiligo
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condition in which patchy areas of depigmentation occur in other wise pigmented skin
- caused by localized death of melanocytes - autoimmunity |
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what cancer do melanocytes give rise to?
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melanoma
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How do melanocytes differ among races?
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Melanocytes differ in the amount of melanin they produce NOT the total number of melanocytes
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Langerhans cells
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- macrophages of stratified squamous epithelium
- derivatives of monocyte-macrophage lineage - involved in processing and presenting of antigens entering through the skin to lymphocytes |
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merkel cells
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- present mainly in thick skin of palms and soles of feet
- contain keratin filaments - bound to keratinocytes by desmosomes - associated with free nerve endings in epidermis - role in mechanoreception - dense in fingertips (fine touch, sensitivity) |
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function of dermis
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- layer of CT that underlies the epidermis, supports it mechanically, and supplies it with blood vessels, lymphatic vessels, and nerves
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composition of dermis
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- collagen and elastic fibers
- resident CT cells including fibroblasts, mast cells, and macrophages - small blood vessels and lymphatic capillaries - nerve supply - sensory structures |
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papillary layer
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- lies directly underneath the epidermis
- function is to provide mechanical, immunological, and metabolic support to epithelium (analogous to lamina propria) - forms dermal papillae - rete ridges - signaling molecules in dermis produce signaling that determine the phenotype of overlying epidermis and of epidermal derivatives |
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reticular layer
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- lies deep to papillary layer
- much thicker and coarser collagen bundles |
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subpapillary plexus
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between papillary layer and reticular layer of dermis
- shunting of blood to plexus allow for release of excess heat - accounts for redness and heat of skin when blood is in superficial layers |
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cutaneous plexus
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between the reticular layer of dermis and hypodermis
- shunting blood to plexus allows for conservation of heat |
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nail bed
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plate of hard keratin that lies on a stratified squamous epithelium
- supports the nail - does not contribute to its growth |
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nail matrix
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- gives rise to nail plate epithelium
- located at proximal end of the nail - dividing cells give rise to hard keratin |
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eponychium or cuticle
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- formed by a fold of stratum corneum of epidermis covering the proximal end of nail
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lunula
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crescent visible at proximal end of nail plate
- visible part of matrix |
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anagen
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period of hair growth
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catagen
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period of hair regression
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telogen
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period of rest
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turnover of scalp follicles
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3-4 years
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sebaceous glands
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- situated in the dermis
- generally associated with hair follicles - alongside hair shaft - made up of layer of rapidly dividing basal cells which lie on basal lamina - secrete sebum - responsive to sex hormones --> become more active after puberty |
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sebum
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secretion from sebaceous glands
- consists mainly of lipid, but also remnants of dead cells - serves as natural emollient - help reduce water loss from skin |
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eccrine sweat glands
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- found deep in dermis or hypodermis
- secretory portion consists of a coiled tubule composed of myoepithelial cells and secretory cells - fluid produced is isotonic plasma but is made hypotonic by reabsorption of some of the electrolyte content by duct cells - sweat contains mainly water, NaCl, urea, ammonia, and uric acid - essential for thermoregulation - sweat glands in thick skin respond to stress - sweat glands in thin skin respond to heat stress |
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apocrine sweat glands
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- similar in structure to eccrine sweat glands
- derived from epidermis - secretory cells produce and secrete a proteinaceous material - do not begin to secret until puberty - found in axilla, areola, and circumanal region |
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free nerve endings
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- enter epidermis from dermis
- respond to temperature and pain - associated with merkel cells |
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pacinian corpuscles
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- look like an onion in section
- located deep in dermis - respond to pressure stimuli |
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meissner's corpuscles
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- located in dermal papillae
- most numerous in fingertips, soles of feet, lips, and genitalic area - oval in shape - composed of nerve endings surrounded by modified schwann cells - touch receptor |
