Integument Flashcards
Skin percentage body mass
15-20%
Skin functions
. Protection against mechanical assaults
. Barrier to biological and chemical and physical agents including UV radiation
. Moisture control
. Thermoregulation
. Sensory reception
. Metabolism (synthesis of vit. D3, removal of excess of electrolytes in sweat)
Epidermis
. Continuously proliferating stratified squamous keratinized epithelium
. Keratinocyte is principal cell
. Includes melanocytes, langerhans cells, Merkel cells
. Thick/thin skin based on thickness of epidermis only (thick on sole of foot and palm of hand, thin everywhere else)
Dermis
. CT, blood vessels, nerves, sensory receptors, and skin appendages
. Epidermis and dermis bound by specialized basement membrane
. Rete ridges: epidermal down growths that extend into superficial dermis and result in formation of dermal upward projections (dermal papillae)
Hypodermis
. SubQ
. Often not soldiered part of skin
Where is the thickest skin?
Upper portion of back
Keratinocytes
. Arise from deepest layer of epidermis
. Move toward free surface as they differentiate
. Contain keratin
. During differentiation they lose mitotic abilities but continue to produce keratin
. Keratin represents about half of total protein in superficial cell layer
Basal layer of epidermis (stratum basale)
. Single layer cuboidal cells separated from dermis by basement membrane
. Hemidesmosomes bind cell to basal lamina
. Desmosomes bind cells to each other
. Keratinocytes frequently under mitosis
Human epidermis renewed every ____
15-30 days
Spinous layer of epidermis (stratum spinosum)
. Prickle cell layer
. Thickest layer
. Keratinocytes produce cytoplasmic intermediate filaments (cytokeratins)
. Cytokeratins form bundles (tonofilaments)
. Aggregates of tonofilaments (tonofibrils)
. Tonofibrils bind to desmosomes btw adjacent keratinocytes
Granular layer of epidermis (stratum granulosum)
. 3-5 layers of flattened cells undergoing keratinization
. Cytoplasm contains basophilic keratohyalin granules and filaggrin protein w/in granules and lamellar granules (golgi-derived w/ lipids)
Stratum lucidum
. Only in thick skin
. Thin layer flattened keratinocytes w/ lost nuclei and organelles and packed keratin filaments
Stratum corneum layer in epidermis
. 15-20 layers of keratinized cells filled w/ keratin filaments
Melanocytes
. Derived from neural crest
. Synthesize melanin that absorbs UV radiation
. Located in stratum basale w/ long processes into stratum spinosum
. Functionally related to 4-10 keratinocytes forming epidermal-melanin unit
. Sends melanosomes to keratinocyte cytoplasm
Carotene
Yellow pigment in skin and adipose that affects skin color
Langerhans cells
. Antigen-presenting cells derived from bone marrow
. 2-8% epidermal cells mostly in stratum spinosum
Merkel cells
. Mechanoreceptor cell that detect light touch
. Located in stratum basale
. Joined by desmosomes to keratinocytes
Papillary dermis
. Dermis immediately adjacent to epidermis
. Has fine collagen fibers and small blood vessels, sensory nerve endings and structures
Reticular dermis
. Deeper, dense irregular CT rich in collagen and elastic fibers
Dermis functions
. Responsible for tone and texture of skin
. When aging the collagen and elastin in upper dermis degenerate and skin loses texture and wrinkles
Nerve endings found in dermis
. meissner’s corpuscles: touch receptors found in papillary dermis
. Pacinian corpuscles: deep pressure receptors in deep dermis and hypodermis
. Ruffini corpuscles: stretch and tension receptors in deep dermis
. Krause end bulbs: mechanoreceptors found in lining of oropharynx and conjunctiva of the eye
Hypodermis
. Loose CT and adipose
. Binds skin loosely to subadjacent organs
. Compartmentilized by fibrous septa running from deep reticular dermis to fascial tissue that underlies hypodermis
. Larger vessels that supply and drain dermal blood vasculature
Sebaceous glands
. Produce sebum (skin lubricant w/ slight antibiotic effect)
. Assoc. w/ hair follicles usually, but can be unrelated (eye like, oral cavity)
. Cluster of 3-5 alveoli
. Secretory cells get larger as they accumulate lipid droplets
. Entire secretory cell is released as product (holocrine)
Sweat glands
. Found everywhere but lip margins and parts of genitalia
. Most abundant on palm of hand and sole of foot
. Eccrine sweat glands
. Simple coiled tubular glands formed by secretory portion (w/in deep reticular dermis) and excretory eccrine duct
. Becomes straight as it ascends vertically through dermis towards skin surface
. Secretory cells are clear, larger cells that secrete bulk of watery sweat and smaller cells that secrete glycoprotein
. Attenuated outer layer of myoepithelial cells that form discontinuous layer btw secretory cells and basement membrane
Apocrine sweat glands
. Limited distribution
. Found in axilla and groin
. Secretory portion in deep reticular dermis or hypodermis
. Secretory portion located in deep reticular dermis or hypodermis and is coiled tubule w/ diliated lumen
. Secretory product discharged via ducts into upper parts of the hair follicle above sebaceous gland
. Not functional until puberty
Where is hair not present?
. Skin of palms and soles
. Lip
. Parts of genitalia
Components of hair
. Shaft: protrudes above the surface of the epidermis
. Root: embedded in skin
Where does hair form?
. W/in epidermal invaginations in hair follicles
. In assoc. w/ sebaceous glands and smooth muscle bundle (arrector pili)
Hair bulb
. Terminal dilation in hair follicle
Dermal papilla
. Contains blood capillaries
. Inserts into base of hair bulb
Keratinocytes continuous w/ ___ layer of epidermis to cover dermal papilla
.basal layer
What occurs during active hair growth?
. Epithelial cells proliferate to form layers of hair follicle
. Undergo keratinization, melanin accumulation and maturation
Medulla in regards to hair
. Center of hair root
Cortex in regards to hair
. Heavily keratinized cels around medulla
Hair cuticle
. Thin layer of keratinized cells covering cortex
Root sheath
. Continuous w/ outermost cells of hair bulb
. Internal root sheath: surrounds initial part of hair root but degenerates over sebaceous gland level
. External root sheath: covers internal sheath and extends to epidermis and is continous w/ strata basale and spinosum
Nails
. Hard players of keratin on dorsal surface of each distal phalanx
. Nail root covered by fold of skin and has cuticle/eponychium (extension of stratum corneum)
. Bound to nail bed (bed of epidermis w/ stratum basale and spinosum)
How is nail root formed?
From nail matrix
. Cells divide, move distally and become keratinized
Hyponychium
. Epidermal fold where distal end of nail plate becomes free of nail bed
