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Functions of the skin
  • Protection against injury, microbial invasion, and loss of body fluid
  • Regulation of body temp
  • Reception of sensory stimuli
  • Excretion from sweat glands
  • Secretion of sebum (sebaceous glands), cerumen (ceruminous glands), milk (mammary glands), tears (lacrimal glands)
  • Synthesis of vitamin D involving UV radiation
Cells of Epidermis (stratified squamous epithelium)
  • Keratinocytes
  • Melanocytes
  • Langerhans cells
  • Merkel cells
  • Make up bulk of cells (stratified squamous epi) (>90%)
  • formation of keratin, protection of skin
  • Derived from neural crest cells
  • Produce melanin pigment
Langerhans cells
  • Bone marrow derived dendritic
  • Function in Ag presentation
  • Can be found in the basal, spinous, and granular layers of epidermis
Merkel cells
  • Derived from neural crest cells
  • Function as sensory (mechanoreceptor) cells for light touch
Layers of the skin (base to surface)
  • Stratum basale (stratum germinativum)
  • Stratum spinosum (prickle cell layer)
  • Stratum granulosum
  • Stratum lucidum
  • Stratum corneum
Stratum basale (stratum germinativum)
  • Basal layer
  • Single layer of cuboidal to low columnar cells are actively mitotic
  • Contains scattered Merkel cells and melanocytes
  • Interdigitates with the dermis and is separated from it by a basement membrane
Stratum spinosum (prickle cell layer)
  • Thickest layer
  • Consists of keratinocytes referred to as prickle cells (mitotically active)
  • Mitotically active layers stratum basale and stratum spinosum can be referred to collectively as the stratum malpighi (malpighian layer)
Stratum granulosum
  • Found only in thick skin
  • Most superficial (in thick skin)
  • 3-5 cells thick
  • keratinocytes normally still retain their nuclei
Stratum lucidum
  • Found only in thick skin
  • Lightly stained
  • Thin layer of keratinocytes w/o nuclei and organelles
Stratum corneum
  • Numerous layers of flattened keratinized cells (squames) that eventually slough off from the surface
  • Derived from mesoderm
  • 2 layers
  • Papillary layer
  • Reticular layer
Papillary layer
  • Superficial layer of dermis
  • Interdigitates with the epidermis forming dermal ridges & epidermal rete ridges (rete apparatus)
  • Consists of loose tissue & contains capillary loops that extend to the dermis - epidermis interface
  • Some contain Meissner's corpuscles which are tactile mechanoreceptors and Krause end bulb (function unknown)
Reticular Layer
  • Deepest layer in dermis
  • Denser and less cellular
  • Characterized by thick irregular bundles of collagen and by coarse elastic fibers
  • Fibers form regular lines of tension in skin called Langer's lines
  • Found in deeper portion are pacinian corpuscles (vibration and pressure) and Raffini corpuscles (mechanoreceptors tensile forces)
  • Also contains sweat glands, hair follicles, and sebaceous glands
Sebaceous glands
  • Holocrine glands
  • Found over surface of body except on palms, soles, and dorsum of feet
  • Largest and most concentrated on face and scalp
Sweat (sudoriferous) glands
  • Eccrine glands
  • Found over surface of body with exception of lips, external ear canal, and labia minora
  • Most conc in thick skin of palms of hands, and soles of feet
  • Function principally in regulating body temperature
Apocrine sweat glands
  • Found only in the axilla, areolae, and anal region
  • Modified apocrine sweat glands include the ceruminous (wax) glands of the external auditory canal, the glands of moll in eyelids, and the mammary glands
Hair follicles
  • Complex structures involving both epidermis and dermis
  • Found over surface of body w/exception of soles of feet, palms of hand, glans penis, clitoris, labia minora, mucocutaneous junctions and portions of fingers and toes
  • Sebaceous glands often open into the hair follicle rather than onto the skin surface, entire unit called pilosebaceous unit
  • Caucasians=oblique
  • Blacks=parallel
  • Asians=vertical
  • 2 types: vellus and terminal
  • fetal hair = lanugo
Vellus hair
  • Soft, fine, short and pale
  • covering eyelids etc
Terminal hairs
  • hard, large, coarse, long and dark
  • scalp and eyebrows, etc
Represent keratinized epithelial cells arranged in plates of hard keratin
  • Deep to reticular layer
  • NOT a part of skin
  • Consists of adipose tissue (panniculus adiposis) variable thickness and panniculus carnosus (deepest)
Panniculus adiposis
  • More superficial layer
  • Contains: deep part of hair follicles, some pacinian corpuscles, and origin of smooth muscle fibers (arrector pili muscles) assc w/hair follicles
Panniculus carnosis
  • More deep than panniculus adiposis
  • largely vestigal in human
  • Can be found in skin of neck, face, and scalp as the platysma and muscles of facial expression
  • Also present in scrotum as the dartos muscle in subareolar nipple muscle and in the palmeris brevis of the hand
  • Circumscribed, flat area of discoloration
  • < 1 cm in diameter
  • elevated circumscribed solid area
  • < 1 cm in diam
  • elevated circumscribed solid area
  • > 1 cm in diam
  • elevated, flat circumscribed area
  • > 1 cm in diam
  • fluid filled raised area
  • < 0.5 cm in diameter
  • Fluid filled raised area
  • > 0.5 cm in diameter (lg vesicle)
Common term for vesicle or bulla
Discrete pus filled area
  • Dry, platelike (squamous) excrescence
  • Result of defect in keratinization
  • Thickened rough skin
  • Characterized by prominent skin markings, usually caused by chronic scratching
  • Traumatic lesion
  • Characterized by disruption of epidermis causing a raw linear area (deep scratch)
  • Boil
  • Localized pyogenic infection originating deep in the hair follicle
  • Large boil
  • Result of confluence of multiple faruncles
Thickening of stratum corneum
Keratinization characterized by retention of nuclei in the cells of the stratum corneum
Disorder of keratinization in which premature keratinization occurs in cells that have not reached the stratum corneum
Hyperplasia of the stratum spinosum
Loss of cellular cohesion, mainly involving the cells of the stratum spinosum
Inflammatory intercellular edema of the epidermis
Linear pattern of melanocyte proliferation w/in the epidermal basal layer
Discontinuity of the skin with partial loss of the epidermis
discontinuity of the skin w/complete loss of the epidermis and often portions of the dermis and hypodermis
Hyperplasia of the papillary dermis with elongation and/or widening of the dermal papillae
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