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CFoM > Day 7: Skin > Flashcards

Day 7: Skin Flashcards

1
Q

keratinocytes (+ functions)

A
  • arise from embryonic ectoderm
  • functions:__​​​​
    • 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?
    • protecting against abrasion/shearing
      • keratinocytes are joined together by desmosomes
        • joined to the basal lamina by hemidesmosomes
      • pemphigus: body makes antibodies against desmoglein (protein in desmosomes)
        • blisters and skin sloughing
    • 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
    • protecting against pathogens
      • ​physical barrier
      • produce antimicrobial peptides and proteins
    • synthesis of vitamin D
      • ​plasmalemma contains precursor of Vitamin D
      • UV radiation transforms/activates
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2
Q

fetal development of skin

A
  • 6 weeks into pregnancy
    • 2 layers; periderm & basal layer
  • 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)
  • ​when stem cells divde:
    • ​metaphase plate perpendicular to basement membrane:
      • ​division results in 2 cells that remain in stratum basale
      • other cell may leave to become keratinocyte–> delamination
    • 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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3
Q

adult homeostasis

stem cell division in the epidermis

A
  • maintenance of layers
  • division parallel and perpendicular to BM
  • renewal of the epidermis every 28-40 days
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4
Q

Langerhans cells

A
  • 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
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5
Q

melanocytes

A
  • 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
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6
Q

synthesis of melanin

A
  • synthesized from the amino acid tyrosine, which requires the activity of the catalytic enzyme tyrosinase
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7
Q

eccrine sweat glands

A
  • simple coiled tubular glands in the dermis
  • primary function: regulation of body temperature
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8
Q

means of regulating temperature - skin

A
  • 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
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9
Q

merkel cells

A
  • 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
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10
Q

Meissner’s corpuscles

A
  • 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
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11
Q

Pacinian corpuscles

A
  • 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
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12
Q

free nerve endings

A
  • 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
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13
Q

proliferative unit

A
  • a stem cell surrounded by about 10 committed cells in the stratum basale
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14
Q

hair growth occurs in 3 phases

A

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)

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15
Q

components of hair follicle

A
  • 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
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16
Q

transport in epidermis

A
  • modes of transport:
    • intercellular
    • transcellular
    • intracellular
  • favorable transport:
    • low MW
    • moderately lipophilic
17
Q

differentiation of keratinocytes through skin layers

18
Q

keratinocytes & production of vitamin D

A
  • keratinocyte
    • 7-dehydrocholesterol –> UV exposure–>
      • pre-vitamin D3
        • VD3 (in blood vessel)
          • 25-OH VD (liver)
            • 1,25 (OH)2D3 (calcitriol) (kidney)
              • stimulates:
                • calcium absorption by GI tract
                • calcium re-absorption by kidney
                • bone resorption by osteoclasts
  • associated with Vitamin D defiency:
    • osteomalacia
    • rickets
    • others
19
Q

three major steps involved in tanning

A
  1. photo-oxidation of melanin
  2. re-distribution of melanin granules to upper layers
  3. increased number of melanin granules
20
Q

ruffini endings

A

skin stretch and joint deformation

21
Q

pemphigus vulgaris

A
  • chronic autoimmune blistering skin disease with the formation of antibodies against desmosomes
22
Q

Stevens Johnson syndrome

A
  • a type of severe skin and mucous membrane reaction characterized by blisters and peeling
23
Q

first-degree burn

A

involves the epidermis only, appears red and dry without blisters

24
Q

superficial second-degree burn

A
  • extends into the papillary layer/upper dermis, appears red and blistered
25
Q

deep second-degree burn

A
  • extends into the reticular / deep dermis, appears yellow or white, may be blistered
26
Q

third-degree burn

A
  • extends through entire dermis, can involve the hypodermis, appear white/brown may be blistered
27
Q

fourth-degree burn

A
  • extends beyond hypodermis into underlying tissue, appears black, dry, and charred
28
Q

melanoma in-situ

A
  • cancer of pigment-containing cells (melanocytes) limited to the epidermis
29
Q

Breslow depth

A
  • refers to the thickness of an invasive melanoma measured from the top of the epidermis to the deepest invasive cells
30
Q

Clark’s level

A
  • a melanoma staining system that describes the level of anatomical invasion based on the layers of the skin
31
Q

squamous cell carcinoma

A
  • skin cancer that forms from the squamouse cells of the epidermis (the uppermost epidermal cells)
32
Q

basal cell carcinoma

A
  • skin cancer that forms from the basal cells of the epidermis
    • (the lowermost epidermal cells)
33
Q

epidermis

A
  • stratified squamous keratinized epithelium
34
Q

dermis

A

dense irregular connective tissue

  • papillary layer
    • knob-like papillae (projections) of connective tissue protrude into the epidermis to assist in binding these two tissues together
      • downward projections of the epidermis are known as interpapillary pegs
    • composed of tightly woven mesh of thin collagen and elastic fibers with some reticular fibers
    • network of capillaries beneath the epidermis
  • reticular layer
    • coarse, densely interwoven collagen, parallel to skin
    • hair follicles, sebaceous and sweat glands, Pacinian corpuscles, and smooth muscle (arrector pili muscle) are located in this layer
35
Q

stratum basale

A

somwhat columnar cells attached to the basement membrane, with added binding strength of hemidesmosomes

36
Q

stratum corneum

A
  • thick layer of tightly packed, flattened, highly modified keratinocytes
  • keratinocyte nucleus is absent and a homogenous filamentous substance, keratin, is deposited on the inside of the plasma membrane, forming a cornified cell envelope
37
Q

stratum lucidum

A
  • layer 3 to 5 cells thick; keratinocytes are flattened and stain feebly, they have lost their nuclei and cytoplasmic organelles
38
Q

stratum granulosum

A
  • keratinocytes are flattened, cytoplasm contains irregularly-shaped keratohyalin granules associated with tonofilaments
  • Lamellar bodies (pale, intracellular) increase in number, and lamellar product is released into the extracellular space when the cells die
39
Q

stratum spinosum

A
  • keratinocytes are “prickle cells”
    • unique spiny intercellular bridges / projections
      • cytoplasmic extensions containing tonofilaments (keratin bundles) attached to an intercellular desmosome
    • ​keratinocytes develop lamellar bodies in this layer

CFoM (7 decks)

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