Day 7: Skin Flashcards
keratinocytes (+ functions)
- arise from embryonic ectoderm
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functions:__
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epidermal structural integrity + strength
- migrating outward from stratum basale, keratinocytes gradually fill with keratin + nucleus degenerates
- in SG: keratin filaments bundle into tonofilaments (with help of filaggrin, constituent of keratohyalin granules)
- tonofilaments attach to desmosomes, strengthen cytoskeleton
- involucrin, loricrin, etc?
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protecting against abrasion/shearing
- keratinocytes are joined together by desmosomes
- joined to the basal lamina by hemidesmosomes
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pemphigus: body makes antibodies against desmoglein (protein in desmosomes)
- blisters and skin sloughing
- keratinocytes are joined together by desmosomes
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protecting against dehydration
- produce lipids and lipoproteins (lamellar bodies)
- released as cells die and fill intercellular spaces
- insoluble structural proteins like involucrin and loricrin contribute to the waterproof barrier
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protecting against pathogens
- physical barrier
- produce antimicrobial peptides and proteins
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synthesis of vitamin D
- plasmalemma contains precursor of Vitamin D
- UV radiation transforms/activates
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epidermal structural integrity + strength
fetal development of skin
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6 weeks into pregnancy
- 2 layers; periderm & basal layer
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2nd trimester
- periderm sloughs off, 4 layers of epidermis develop
- stratum basal contains stem cells, but only one cell in ~10 in the basal layer produce daughter stem cells, other cells in this pack can divide, but differentiate into keratinocytes (proliferative unit)
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when stem cells divde:
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metaphase plate perpendicular to basement membrane:
- division results in 2 cells that remain in stratum basale
- other cell may leave to become keratinocyte–> delamination
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metaphase plate parallel to basement membrane:
- one daughter cell remains in the stratum basale
- other commits to becoming a keratinocyte in the stratum spinosum
- during early embryonic develpment, most divisions occurs perpendicular, so daughter cells remain in stratum basale to increase surface are of skin
- during maturation + skin thickening, more stem cells divide parallel to increase production of cells that differentiate into keratinocytes
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metaphase plate perpendicular to basement membrane:
adult homeostasis
stem cell division in the epidermis
- maintenance of layers
- division parallel and perpendicular to BM
- renewal of the epidermis every 28-40 days
Langerhans cells
- occur among keratinocytes in all layers, but are most common in the stratum spinosum
- arise from common myeloid progenitors in BM
- component of mononuclear phagocytic system
- antigen-presenting cells: phagocytose antigens, migrate to lymph nodes, and present the antigen to T-helper lymphocytes
- may also play a role in immune tolerance
- originate from yolk sac/fetal liver
melanocytes
- arise from the neural crest of the developing embryo
- protect the integument and underlying tissues against UV radiation
- large cells, cytoplasm appears empty and unpigmented
- their intracellular immature melanosomes (where pigment melanin is stored) do not become dark until they mature and transfer to keratinocytes
- cytocrine secretion: transfer pigment through tips of their melanosome-containing dendrites that fuse with neighboring keratinocytes
- melanin granules concentrate near the nucleus, which helps protect the dividing cells from UV damage
- differences in skin color are not due to differences in melanocytes but in the amount of melanin the melanocytes produce.
- dark skinned individuals: more melanin, more melanosomes are larger, and there is an increase in the transfer of melanin from melanocytes to keratinocytes
synthesis of melanin
- synthesized from the amino acid tyrosine, which requires the activity of the catalytic enzyme tyrosinase
eccrine sweat glands
- simple coiled tubular glands in the dermis
- primary function: regulation of body temperature
means of regulating temperature - skin
- sweat glands
- balanced vasodilation and vasoconstriction of networks of small blood vessels in the dermis also regulate body temperature
- skin in the extremities contains arterio-venous anastomoses that modulate the flow of blood to and from the surface of the body and thus the amount of heat exhange
merkel cells
- cells specialized in the sense of (gentle) touch
- located in the stratum basale of the epidermis
- innervated by myelinated sensory nerve fibers that become unmyelinated as they cross the basement membrane and form expanded endings that contact the surface
Meissner’s corpuscles
- spiraled unmyelinated axon surrounded by modified Schwann cells that are flattened and arranged as encircling horizontal lamellae
- most abundant in the dermal papillae in the fingertips, palms, soles of the feet, lips, face
- areas that are sensitive to light touch
Pacinian corpuscles
- central sensory axon located in a fluid-filled cavity surrounded by 20 to 60 concentric lamellae of thin, flat, modified Schwann cells
- detect deep pressure and high frequency vibration
- less frequent in the skin than Merkel cells or Meissner’s corpuscles
free nerve endings
- unencapsulated sensory axons that penetrate the epidermis and end in the stratum granulosum
- detect polymodal receptors and are thought to detect hot/cold, pain, pressure, and itch
proliferative unit
- a stem cell surrounded by about 10 committed cells in the stratum basale
hair growth occurs in 3 phases
Anagen: phase of active growth; this usually lasts 2 to 6 years for scalp hair (length of hair is dependent upon the duration of this cycle (90% of scalp hair)
Catagen: brief phase of reduced hair growth in which the length of the hair follcle shortens (3 weeks) (about 1% of scalp hairs)
Telogen: resting phase that lasts 2 to 4 months. At the end, hair is shed from the follicle, cycle begins anew (10-15% of scalp hair)
components of hair follicle
- bulge
- location of stem cells
- re-populate hair bulb after telogen phase
- SC can migrate to epidermis
- matrix
- dividing epithelial cells responsible for hair growth