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MM Test 2 > B6.025 Skin Development > Flashcards

B6.025 Skin Development Flashcards

1
Q

functions of the skin

A 
part of integumentary system
protects inner body from the environment
involved in thermoregulation via blood vessels and glands
storage center for lipids and water
sensation
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2
Q

size of the skin

A

largest organ in the body

0.5mm-4mm thickness

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3
Q

excretion functions of skin

A

sweat removes water, small amounts of salt, uric acid, and ammonia

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4
Q

blood reservoir of skin

A

dermal blood vessels carry 8-10% of total blood flow in resting adult

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5
Q

function of skin in the synthesis of vitamin D

A

requires UV rays

later converts to calcitriol (in liver and kidney) that aids in absorption of calcium

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6
Q

origin of epidermis

A

non neural ectoderm

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7
Q

examples of epidermal appendages

A

hair follicles
apocrine & eccrine sweat glands
mammary glands
nails

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8
Q

neural ectoderm (neural crest cell) derivatives

A

melanocytes
nerves and sensory receptors
cranial mesenchyme/CT

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9
Q

ectodermal germ layer derivatives in skin

A

epidermis
epidermal appendages
neural ectoderm derivatives

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10
Q

mesodermal germ layer derivatives in skin

A 
dermis
hypodermis
blood and lymph vessels
Langerhans cells, fibrocytes, adipocytes
muscles
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11
Q

type of muscle in mesodermal germ layer of skin

A

erector pilli in hair follicles

smooth muscle within glands is an ectodermal derivative

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12
Q

how is skin connected to underlying fascia

A

retinacular system

-retinacular “ligaments”, blood vessels, nerves, and lymphatics

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13
Q

function of retinacular system

A

connection of skin to fascia
limitation of skin movements
-tether skin to fascia so 2 tissue planes glide on each other

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14
Q

what are skin wrinkles

A

visible signs of aging of retinacular components

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15
Q

skin formation at 5 weeks

A

2 germ layers + neural crest cells

  • non neural ectoderm
  • neural ectoderm
  • mesodermal mesenchyme
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16
Q

formation of the epidermis in the 2-4 month of development

A

ectoderm divides to form an overlying layer of flattened cells (periderm) in week 5
basal layer cells proliferate to form intermediate layer

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17
Q

describe the periderm

A

flat cells that are cast off in development in amniotic fluid

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18
Q

5 layers of epidermis

A

from top to bottom:

  • stratum corneum
  • stratum lucidum (only in thick skin)
  • stratum granulosum
  • stratum spinosum
  • stratum basale
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19
Q

how do the 5 layers of epidermis form?

A

keratinocytes form and differentiate as they move to higher layers
eventually these die and form stratum corneum

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20
Q

stratum corneum

A

closely packed dead cells containing keratin

-protects and waterproofs

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21
Q

stratum lucidum

A

extra layer of dead cells in thick skin such as soles/palms

-provides extra protection

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22
Q

stratum granulosum

A

cells containing kerato-hyaline granules

-keratin precursors

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23
Q

stratum spinosum

A

polyhedral cells with tonofibrils (intracellular filaments)
-converge on desmosomes
Langerhans cells prominent
-phagocytose

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24
Q

stratum basale

A

produces new cells that move into upper layers
forms ridges/hollows reflected in fingerprints
contains melanocytes

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25
Q

function of melanocytes

A

makes pigment/melanin in melanosomes

transported to keratinocytes and hair bulb

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26
Q

cell types found in the epidermis

A

keratinocytes
melanocytes
Merkel cells
Langerhans cells

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27
Q

role of keratinocytes in skin

A
  • make up 90% of epidermis (formed in basal layer and push way up to surface)
  • function to form barrier against environmental damage via keratinization (keratin protein production and terminal differentiation and shedding)
  • protect against pathogens, fungi, parasites, viruses, heat, UV radiation, water loss
  • produce pro-inflammatory mediators to attract leukocytes to site of pathogen invasion
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28
Q

what is Harlequin Ichthyosis

A

excessive keratinization of the skin
keratin layers crack to form fissures
hereditary disorder: either autosomal or X linked recessive

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29
Q

symptoms of Harlequin Ichthyosis

A

difficult to control water loss, regulate body temp, and fight infections due to disruption of barrier
some infants survive to childhood and adolescence

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30
Q

how does the neural tube give rise to melanocytes

A

neural tube comprised of neural ectoderms
a subset undergoes epithelial to mesenchymal transformation (EMT)
neural crest cells leave tube and migrate to form new structures (including melanocytes)

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31
Q

function of melanocytes

A

located in stratum basale
branch to form dendrites
produce melanin that accumulates in melanosomes
also present in hair follices

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32
Q

movement/function of melanin in the skin

A

dermal melanin transported along dendrites to keratinocytes
accumulates on superficial aspect of keratinocytes
shields keratinocytes from harmful UV light

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33
Q

albinism

A

globally reduced or absent pigmentation (skin, hair eyes)

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34
Q

vitiligo

A

loss of melanocytes in patches of skin, hair, and oral mucosa due to an autoimmune disorder

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35
Q

piebaldism

A

patchy absence of hair pigment

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36
Q

waardenburg syndrome

A

patches of white skin and hair
irises of different colors
deafness

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37
Q

description of merkel cells

A

originate from epidermis
found in stratum basale
attached to keratinocytes via desmosomes

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38
Q

function of merkel cells

A

make contact with sensory nerve fibers (Merkel nerve endings)
mechanoreceptors
react to low vibrations and pressures over long periods

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39
Q

where are merkel cells present in the body

A

high density on fingertips and lips/face

40
Q

description of Langerhans cells

A

star shaped dendritic cells arising from BM (mesodermal) that migrate to epidermis
found throughout epidermis, but prominent in stratum spinosum

41
Q

function of Langerhans cells in skin

A

antigen presenting immune cells
phagocytic
easily damaged by UV light

42
Q

dermis formation

A

formed from corium during 3rd and 4th months of development

43
Q

what is the origin of the dermis

A

mesenchyme of 3 sources
lateral plate mesoderm (parietal)
paraxial mesoderm
neural crest cells (neural ectoderm)

44
Q

lateral plate mesoderm dermis derivatives

A

dermis of limbs and body wall

45
Q

paraxial mesoderm dermis derivatives

A

dermis of back

46
Q

neural crest cell dermis derivatives

A

dermis of face and neck

47
Q

components of dermis

A 
connective tissue
fibroblasts
blood vessels
sensory nerve endings
oil and sweat glands
hair follicles
48
Q

what is the papillary layer of dermis

A

forms irregular dermal papillae which project upward into the epidermis

49
Q

retinacular layer of dermis

A

inner dermis

50
Q

function of papillary layer

A

supports overlying epidermis
ridges increase surface area for exchange of oxygen, nutrients, and waste
increased surface area also prevents separation of dermal and epidermal layers
dermal papillae play role in hair formation, growth, and cycling

51
Q

composition of reticular layer

A

composed of dense irregular connective tissue

densely packed collagen, elastic, and reticular fibers

52
Q

orientation of collagen fibers in reticular layer

A

creates lines of tension, Langer’s lines

relevant to wound healing/surgical procedures: incisions made parallel may heal better and produce less scarring

53
Q

properties of reticular layer

A

strength, extensibility, elasticity

contains roots of hair and hair bulbs (bases of hair follicles)

54
Q

describe the skin at birth

A

Vernix Caseosa

whitish paste formed by secretions from sebaceous glands, degenerated epidermal cells, and degenerated lanugo hair

55
Q

function of vernix caseosa

A

covers skin

protects against macerating action of amniotic fluid

56
Q

what are epidermal appendages

A

derivatives of epidermis
develop as downgrowths of epidermis into dermis
dermis provides signals that lead to differentiated structures

57
Q

examples of epidermal appendages

A 
hair follicles
sweat glands
sebaceous glands
mammary glands
nails
58
Q

functions of hair follicles

A

involved in thermoregulation

provide protection from sun/elements

59
Q

initial development of hair follicles

A

first in cranial region (9th week)

by 5th month, most are formed (5 mil)

60
Q

hair follicle development

A
  1. solid epidermal proliferations from stratum basale project and penetrate underlying dermis
  2. terminal end (hair bud) invaginates to form hair papilla
  3. hair papilla fills with mesoderm in which vessels and nerve endings develop
  4. cells in hair bud center become spindle shaped and keratinized to form the hair shaft
  5. cells in periphery become cuboidal and form the epithelial hair sheath
  6. surrounding mesenchyme forms the dermal root sheath and a small smooth muscle attachment (erector pili)
61
Q

how does hair grow

A

via continuous proliferation of epithelial cells at the follicle base/ hair bulb that pushes hair up the shaft

62
Q

what is the erector pili

A

small smooth muscle (mesoderm derivative) attached to the dermal root sheath

63
Q

function of erector pili

A

contracts in response to cold, emotional state (adrenaline)
creates shallow depression on the skin surface; thus protrusion of surrounding area (goose bump)
contraction causes hair to stand up
role in insulation/warmth

64
Q

first hair on a fetus

A

lanugo
appears on eyebrow and upper lip
shed at time of birth

65
Q

hair development in newborn

A

coarser hair arises from new hair follicles after birth

melanin is transferred to hair forming cells several weeks before birth to give hair color

66
Q

process of sebum production

A
  1. small bud grows from epithelial wall of hair follicle and penetrates mesoderm
  2. sebaceous glands are formed from cells in bud
  3. cells in center of gland degenerate, forming sebum that is secreted into hair follicle and reaches skin
67
Q

hypertrichosis

A

excessive hairiness
overabundance of hair follicles
can be focal or over entire body

68
Q

atrichia

A

congenital absence of hair

can be associated with other defects in ectodermal derivatives (teeth, nails)

69
Q

2 types of sweat glands

A

eccrine (do not lose cytoplasm in their secretions)

apocrine (release some of their cytoplasm into their secretions)

70
Q

eccrine gland description

A

form in skin over most of body, high density in palms and soles
form from buds in stratum basale of epidermis that grow down into dermis
end portion coils to form secretory part
epidermal buds also give rise to smooth muscle cells associated with glands

71
Q

function of eccrine glands

A 
function by merocrine mechanisms (exocytosis)
function in temperature control soon after birth
72
Q

apocrine gland description

A

develop from down growths of stratum basale
form where body hair is found (axilla, pubic region)
form from same epidermal buds that give rise to hair follicles
form during puberty
open onto hair follicle (not skin)

73
Q

function of apocrine glands

A

produce sweat
odor due to bacteria that break down products in sweat
portion of secretory cells is shed ins secretion

74
Q

components of sweat

A

lipids
proteins
pheremones

75
Q

sebaceous gland development

A

develop as buds from hair follicle epidermal wall (week 5)

76
Q

function of sebaceous glands

A 
secrete vernix/sebum (oily)
function to lubricate skin and hair
77
Q

what are mammary glands

A

modified apocrine sweat glands

78
Q

development of mammary glands

A

first appear as epidermal mammary lines/ridges in BOTH sexes
at 7 weeks: lines extend bilaterally from base of forelimb to hindlimb region
16-24 epithelial buds of mammary ridge penetrates underlying mesenchyme and form secondary buds
near term: sprouts canalize to form lactiferous ducts

79
Q

mammary line formation

A

most disappears shortly after it forms

small portion persists in thoracic region, penetrating underlying mesenchyme

80
Q

development of lactiferous ducts

A

prenatally: ducts open into epithelial pit
after birth: pit is transformed into a nipple by proliferation of underlying mesenchyme and epithelial pit everts
at birth duct lacks alveoli and secretory structures
at puberty: increased hormones in females stimulate gland enlargement, ductal development, and breast enlargement

81
Q

polythelia

A

accessory nipples due to persistence of mammary line

82
Q

polymastia

A

remnant of mammary line develops into complete breast

83
Q

inverted nipples

A

lactiferous ducts open into epithelial pit that failed to evert

84
Q

gynecomastia

A

excessive development of male mammary gland
can occur transiently in newborns due to maternal sex hormones OR when there is decreased ratio of testosterone to estradiol (Klinefelter XXY)

85
Q

nail development

A
  1. epidermal thickenings appear at tips of digits and form nail fields at 10 weeks
  2. fields migrate to dorsal side of each digit
  3. fields grow proximally, forming a nail root
  4. proliferation of tissue surrounding each field creates a depression for each nail
  5. from nail root, epidermis differentiates into finger and toe nails
  6. nails extend to tips of digits in 9th month of development
86
Q

what is the hypodermis

A

superficial fascia layer under skin

87
Q

function of hypodermis

A

attaches skin to underlying bones, muscles, and deep fascia
attaches to overlying dermis via collagen and elastin fibers
provides blood and nerve supply to underlying bones, muscles

88
Q

what is the hypodermis made of

A 
loose CT
fibroblasts
adipose cells
macrophages
derived from mesoderm but NOT dermatome
89
Q

cutis aplasia

A

congenital absence of the skin, generally isolated lesions on the scalp

90
Q

cutis laxia

A

skin is inelastic and hangs loosely in folds due to decrease or absence of elastin
may be caused by genetic mutation in elastin of fibulins

91
Q

Ehlers Danlos

A

fragile, bruisable skin that heals with peculiar scars

caused by mutation in collagen and altered collagen synthesis

92
Q

epidermolysis bullosa simplex

A

autosomal dominant disease of keratin (filaments aggregate)

skin is fragile, thus non scarring blisters result from little or no trauma

93
Q

wound healing characteristics of embryonic skin

A

rapid
efficient
decreased platelet aggregation/degranulation events
decreased immune response
altered ECM (more type 3 collagen and hyaluronic acid)
scarless

94
Q

discuss the rapid nature of embryonic wound healing

A

gap in embryonic epidermis closed by contraction of a rapidly assembles actin “purse string”

95
Q

discuss the efficient nature of embryonic wound healing

A

standard fibroblasts exert tractional forces to bring wound margins close together

96
Q

adult wound healing

A

slower and less efficient
epidermal cells migrate over exposed substratum to close a gap
specialized myofibroblasts aid in CT contraction

MM Test 2 (23 decks)

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