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VET 411: Skin > Skin Development & Microanatomy > Flashcards

Skin Development & Microanatomy Flashcards

1
Q

what germ layers is skin derived from

A

ectoderm
mesoderm

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2
Q

what structures are derived from ectoderm

A

epidermis
hair follicles
sweat glands
sebaceous glands
modified glands

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3
Q

what structures are derived from mesoderm

A

dermis + subcutis
- dermal matrix (collagen, elastin, proteoglycans)
- vessels/lymphatics
- nerves
- arrector pili muscle
- subcutaneous fat

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4
Q

what does skin thickness depend on

A

thickness of the DERMIS

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5
Q

what are 3 general causes of increased skin thickness

A
  1. increased cellularity from inflammation
  2. neoplastic infiltrate
  3. matrix deposition/fluid in the dermis
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6
Q

what cell types are present in the epidermis

A
  1. keratinocytes
  2. melanocytes
  3. langerhans cells
  4. merkel cells
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7
Q

function of keratinocytes

A

create a barrier to the outside

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8
Q

structure of keratinocytes

A

stratified (4-5 cell layers)

  • stratum basale
  • stratum spinosum
  • stratum granulosum
  • stratum corneum
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9
Q

basal layers (stratum basale)

A

innermost layer

contains germinal cells that undergo mitosis to form undifferentiated keratinocytes

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10
Q

spinous layer (stratum spinosum)

A

middle 1-2 layers of cells that differentiate into keratinocytes

begin to flatten

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11
Q

granular layer (stratum granulosum)

A

cells that begin producing components of the lipid envelope for the cornified layer

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12
Q

cornified layer (stratum corneum)

A

outermost layer of dead keratinocytes

acts as a barrier to and communicates with the environment

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13
Q

types of cornified layers

A

compact
basket weave

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14
Q

compact cornified layer

A

seen in glabrous (hairless) skin and regions under constant pressure/friction

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15
Q

basket-weave cornified layer

A

seen in normal haired skin

high lipid content causes loose arrangement of keratin lamellae

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16
Q

lipid envelope

A

connects dead keratinocytes together in the cornified layer

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17
Q

what connective structures are used to connect keratinocytes

A

desmosomes
tight junctions
E-cadherins

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18
Q

desmosomes

A

connect keratinocytes to each other
- should NOT be visible in health

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19
Q

spongiosis

A

intercellular edema causing keratinocytes to separate

desmosomes become visible

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20
Q

tight junctions

A

prevent passage of molecules through intercellular spaces to require them to pass within the cells via diffusion/active transport
- maintains health of keratinocytes without needing blood supply

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21
Q

E-cadherins

A

connects keratinocytes to each other, to melanocytes, and to langerhans cells

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22
Q
A
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23
Q

what determines the thickness of the epidermis

A

the thickness of the SPINOUS layer

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24
Q

epidermal thickness vs hair coat

A

glabrous (hairless) = thick epidermis

haired = thin epidermis

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25
Q

is epidermal atrophy common

A

no, rare

caused by hyperadrenocorticism

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26
Q

what is epidermal turnover

A

the time it takes for basal cells to reach the cornified layer

takes 3 weeks

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27
Q

immunologic properties of keratinocytes

A
  • normal flora/microbiome
  • antimicrobial peptides
  • lipids
  • cytokines/chemokines
  • express MHC II to act as APCs to T cells in the epidermis
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28
Q

epidermal hyperplasia

A

acanthosis

increased thickness of the epidermis caused by chronic irritation (to the cells or the envelope)

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29
Q

steps of acanthosis

A
  1. injury/irritation causes rapid basal cell division
  2. spinous layer thickens
  3. increased turnover rate
  4. decreased transit time between layers
  5. decreased differentiation
  6. changes in granular and keratin layer
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30
Q

subacute acanthosis lesions

A
  • hypogranulosis: lack of granular layer (dec. differentiation)
  • parakeratosis: retention of nuclei in keratin layer
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31
Q

chronic acanthosis lesions

A
  • hypergranulosis: adaptation to high turnover
  • compact hyperkeratosis: compaction of the cornified layer despite haired skin
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32
Q

melanocytes

A

provide pigmentation to the skin and hair coat

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33
Q

location of melanocytes

A

between basal keratinocytes

extend dendritic processes that carry melanosomes to surrounding keratinocytes

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34
Q

melanosomes

A

synthesize and store melanin pigments

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35
Q

hyperpigmentation

A

excess melanin stimulating hormone (MSH) caused by chronic irritation or solar exposure

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36
Q

depigmentation

A

loss of skin or hair pigment caused by injury to the dermis-epidermis junction and basal cells OR matricidal cells of the hair bulbs leading to melanocyte damage

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37
Q

leukoderma

A

depigmentation of the epidermis

38
Q

leukotrichia

A

depigmentation of the hair coat

39
Q

merkel cells

A

oval receptor cells located in the epidermis

synapse with somatosensory afferent nerve fibers to sense light touch, shape, and textures

also have a neuroendocrine function

40
Q

what are other sensory cells in the skin

A
  • merkel cells
  • tylotrich pads
  • vibrissae
41
Q

langerhans cells

A

epidermal dendritic APCs

used for immune surveillance

42
Q

where are langerhans cells located

A

in the epidermis and hair follicle epithelium

43
Q

function of langerhans cells

A

sample antigens from the environment on the skin surface –> detach from the adjacent keratinocyte –> migrate to draining lymph node –> present to lymphocytes to initiate an immune response

44
Q

what type of immune response do langerhans cells initiate

A

adaptive immune response

45
Q

what is the function of collagen

A

provide tensile strength

46
Q

what is the function of elastin

A

provide elasticity

47
Q

what is the function of proteoglycans

A

provide pliability

48
Q

dermal dendritic APCs

A

provide immunosurveillance in the dermis

sample antigens from dermis –> migrate to draining lymph node –> initiate response

49
Q

what type of immune response to dermal dendritic APCs initiate

A

adaptive immune response

50
Q

basement membrane zone

A

complex structure of proteins and glycoproteins that connects the epidermis and dermis

NOT visible on H&E

51
Q

dermo-epidermal separation

A

defects in the basement membrane zone that lead to separation of the dermis from the epidermis

52
Q

panniculus vs subcutis

A

panniculus - around the panniculus muscle

subcutis - underneath the panniculus muscle

53
Q

panniculus muscle

A

thin muscle layer attached to the skin underneath the dermis

54
Q

panniculus fat

A

fat located directly below the dermis (above the panniculus muscle)

55
Q

subcutaneous fat

A

fat located directly below the panniculus muscle (in the subcutis)

develops independently of panniculus fat

56
Q

panniculitis

A

inflammation in the fatty tissue under the dermis (panniculus or subcutis)

57
Q

cellulitis

A

inflammation of the subcutaneous fat due to infection

58
Q

hair follicles

A

extensions of the epidermis

develops from germinal cells in the epidermis that grow downwards along with keratinocytes

59
Q

infundibulum

A

superficial portion of the hair follicle that opens into the orifice of the follicle

60
Q

what is the epithelium of the infundibulum

A

epidermis

61
Q

where are the majority of the immune cells in hair follicles located

A

infundibulum (CD4 and CD8 T cells, langerhans cells)

62
Q

isthmus

A

middle portion of the hair follicle that includes the bulge

63
Q

bulge

A

location of the follicular stem cells and melanocyte stem cells

present throughout life

forms new anlagen phase and pigmentation of hair shaft

64
Q

supra-bulbar and bulb regions

A

deepest portions of the hair follicle

65
Q

compound hair follicles

A

one primary hair follicle + several secondary hair follicles grouped together

all hair exits through one follicular opening

dogs, cats, rabbits, sheep, goats

66
Q

primary follicles

A

produce guard hairs

67
Q

secondary follicles

A

produce undercoat/wool

NO sweat glands or arrector pili muscle

more secondary follicles = higher quality wool

68
Q

simple hair follicles

A

one primary hair shaft exits from the follicular opening

horse, cattle, pigs, sheep, goats

69
Q

what does hair growth cyclicity depend on

A

breed: continuously growing vs prolonged telogen
seasonal synchronized shedding: daylight and temp
body location: mane and tail vs body

70
Q

what controls cyclic growth

A

growth factors
hormones (T4, cortisol)

71
Q

effect of thyroid hormone on hair growth

A

maintains hair growth and anagen phase

hypothyroid –> shuts down hair follicles

72
Q

effect of cortisol on hair growth

A

initiates anagen phase

73
Q

anagen phase

A

growing phase

  • follicles extend down to subcutis
  • fully developed dermal papilla
  • hair shaft fully formed/growing
74
Q

do anagen follicles have immune activity

A

NO - follicular keratinocytes release anti-inflammatory cytokines to counteract IFN-y by preventing follicles from expressing MHC I

75
Q

catagen phase

A

transition phase

  • involution of epithelium to initiate detachment of hair bulb
76
Q

telogen phase

A

resting phase

  • hair detaches from bulb
  • shaft is only connected to epithelium by keratin plug (club)
77
Q

exogen phase

A

old hair is pushed out when new anagen phase begins

78
Q

what controls sweat glands

A
  • hypothalamus
  • sympathetic NS
79
Q

do rodents have sweat glands

A

no

80
Q

epitrichial glands

A

apocrine glands
ducts open into hair follicles
- barrier
- pheromone release
- lipid excretion
- thermoregulation

generalized: dogs, cats, horses, ruminants

axillary/inguinal: humans

81
Q

atrichial glands

A

eccrine glands
ducts open directly onto the skin surface
- temperature control
- “seal” epidermis
- secrete electrolytes

paw pads/lip/nose: dogs, cats, ruminants

generalized: humans

82
Q

modified sweat glands

A

naslabial glands
ceruminous glands (otitis externa)
mammary glands
anal sac glands
mammalian scent glands

83
Q

sebaceous glands

A

holocrine gland - balls of cells without a lumen; cells in the center undergo cell death

located in the mid-dermis and open into the isthmus area of the hair follicle

  • secrete protective lipids for hair coat/skin
  • innate immune function
  • removal of follicular keratin
  • guide hair shaft through canal
  • pheromones
84
Q

sebum

A

contains lipids and dead sebocytes

85
Q

what stimulates sebaceous gland hyperplasia

A

androgens

86
Q

what stimulates sebaceous gland involution

A

estrogens
glucocorticoids

87
Q

dermal vasculature

A

3 main plexi:
1. superficial plexus
2. mid-dermal plexus
3. deep plexus

88
Q

superficial plexus

A

located directly under the epidermis

89
Q

mid-dermal plexus

A

surrounds the hair follicles at the level of the sebaceous glands

90
Q

deep plexus

A

located in deep dermis/subcutis

91
Q

vasculitis

A

acute vascular wall damage leading to infarction/necrosis of the skin

92
Q

chronic vasculitis

A

chronic, low grade damage leading to ischemia and atrophy of the follicles causing ischemic collagen change

VET 411: Skin (16 decks)

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