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21 fall: histology > Lecture 11 skin > Flashcards

Lecture 11 skin Flashcards

1
Q

Skin functions

A

maintains body temperature

vitamin D synthesis (hormone, not a vitamin)

barrier

  • loss of body fluid
  • mechanical injury
  • noxious agents
  • immunological barriers against pathogen
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2
Q

layers of skin

A

epidermis

dermis

hypodermis (sub Q)

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3
Q

Development of skin

A

epidermis and its appendages are derived from ectoderm

dermis, hypodermis and vascular elements of these tissues are derived from mesoderm

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4
Q

5 layers of epidermis

A
  1. stratum corneum
  2. stratum lucidum
  3. stratum granulosum/ granular layer
  4. stratum spinosum/spinous layer
  5. stratum basale/basal layer
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5
Q

the main parenchymal cell type of the epidermis

A

epidermal keratinocytes

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6
Q

Keratinocytes are characterized by expression of ___

A

cytokeratin genes

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7
Q

keratins proteins encoded by a large ___

A

gene family (54 in humans)

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8
Q

epidermal keratinocytes are considered prototypical ___

A

intermediate filaments

  • larger than actin filaments and microtubules but smaller than myosin
  • play a basic structural role/ provide mechanical strength
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9
Q

type 1 (acid) and type 2 (basic) cytokeratins always form ___

A

heterodimers

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10
Q

basal layer of epidermis expresses Keratin ___

A

5 and 14

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11
Q

granular layer of epidermis expresses keratin ___

A

1 and 10

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12
Q

cytokeratin filaments are anchored by ___

A

desmosomes

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13
Q

DIFC

A

desmosome-intermediate filament complexes

Desmocollin and desmoglein

bind to plakophilin and plakoglobin

which bind to desmoplakin

which bind to intermediate filaments

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14
Q

main categories of skin

A

thick or thin

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15
Q

layers of thin skin

A

stratum basale

stratum spinosum

stratum granulosum

stratum corneum

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16
Q

layers of thick skin

A

stratum basale

stratum spinosum

stratum granulosum

stratum lucidum (extra layer)

stratum corneum

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17
Q

differences between thin and thick skin

A

thick:

5 layers (stratum lucidum)

lack most appendages (hair follicles, sebacous glands, smooth muscle) but does have eccrine sweat glands

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18
Q

Basal Layer

A

germinativum

deepest layer of epidermis

single layer of columnar or cuboidal cells directely attached to the basement membrane by hemidesmosomes

basal cells (basal keratinocytes) are the stem cells of the epidermis

mitosis occurs in vertical manner, one daughter cell ramins basal while the other moves into the stratum spinosum asymmetric division

mitotic activity replenished the cells in the intermediate layers while the most superficial cells (stratum corneum) are shed (homeostasis)

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19
Q

stratum basale are attached to basement membrane by ___

A

hemidesmosomes

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20
Q

what are the stem cells of the epidermis

A

basal cells (basal keratinocytes)

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21
Q

mitosis occurs in a vertical manner in stratum basale, one daughter cell remains basal the other moved into the stratum spinosum. This is called ___

A

asymmetric division

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22
Q

Stratum spinosum

A

“Spiny layer”

irregular, heterogenous

can see “bridges(desmosomes)” between cells

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23
Q

why can you see the desmosomes of stratum spinosum

A

artifact from making the slide

cells retract from each other but stuck at “bridges”

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24
Q

stratum granulosum

A

in thick skin: several layers of flattened cells

in thin skin: can be one layer of cells

keratohyalin granules

-also contain membrane coating lipid granules, secreted by exocytosis onto the surface of the cells, providing a hydrophobic barrier to water

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25
Q

keratohyalin granules

A

found in stratum granulosum

contain filaggrin, which associates the cross links keratin filaments

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26
Q

Stratum lucidum

A

only present in thick skin

  • several layer of flattened dead cells
  • nuclei begin to degenerate, only faint nuclear outlines present here
  • cells are constantly shedding from most superficial layer
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27
Q

in statrum lucidum, ___ begin to degenerate

A

nuclei

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28
Q

stratum corneum

A

outermost layer of epidermis

cells are completely filled by keratin filaments

no longer have nuclei

very flat

space between cells filled with lipids, giving the appearance of continuous sheet of keratin

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29
Q

JEB

A

junctional epidermolysis bullosa

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30
Q

junctional epidermolysis bullosa

A

-defect in the formation of effective hemidesmosomes

severe and often lethal genetic disease

  • very fragile skin, blisters, sloughing, prone to infection
  • monogenic disease caused by mutations in any:

laminin

collagen XVII

integrin a6B4

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31
Q

mutations in what genes leads to junctional epidermolysis bullosa

A

laminin

collagen XVII

Integrin alpha6Beta4 (what hemidesmosomes are made out of)

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32
Q

loss of function mutation in LAMB3 caused

A

blistering and infection (staph) and loss of 60% of skin

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33
Q

junctional epidermolysis bullosa was treated by

A

making skin graphs that had the LAMB3 gene corrected

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34
Q

melanocytes

A

neural-crest derived cells

produce the dark brown pigment melanin from tyrosine

Melanin is synthesized in melanosomes, which then transit along the cytoplasmic extension and are transferred into keratinocytes

lie on basal membrane, attached by hemidesmosomes

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35
Q

melanin is synthesized in

A

melanosomes

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36
Q

melanosomes transit along the cytoplasmic extensions and are transferred into ___

A

keratinocytes

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37
Q

melanocytes lie upon the basement membrane between the ___ of the stratum basale

A

keratinocytes

38
Q

melanocytes send fine processes between other cells and transfer melanin to ___, mainly to the basal cells

A

keratinocytes

39
Q

the fine processes of melanocytes invade the ___ and bud off part of the melanocyte cytoplasm, including the ___

A

keratinocytes

melanosomes

40
Q

melanin protects the chromosomes of the mitotically active basal cells against ___

A

UV-induced damge

41
Q

__ produced by the pituitary and the adrenal glands affect pigmentation

A

hormones

42
Q

langerhans cells

A

morphologically similar to melanocytes, but are actually immune cells

Dendritic cells

fine processes form a network between cells where they can eat antigens which enter the epidermis

after langerhans cells eat antigen, they will migrate to lymph nodes to “present” antigen to T cells which will initiate an immune response

43
Q

Merkel Cells

A

neuroendocrine cells

derived from epithelial proto-basal cells

scattered throughout the stratum basale, mostly found in thick skin

“touch cells”- transmit sensory information via direct innervation

44
Q

merkel cells are found mostly in ___

A

thich skin

45
Q

Merkel cells act as ___

A

touch sensors- transmit sensory information via direct innervation

46
Q

it is hard to see merkel cells using ___, easier to see using ___

A

light microscope

electron microscopy - dense core granules

by their immunocytochemical staining profile (express keratin 8)

47
Q

Dermis

A

thick layer of connective tissue to which the epidermis is attached

48
Q

dermis is akin to ___ in mucosal tissue

A

lamina propria

49
Q

two sublayers of dermis

A

papillary layer

reticular layer

50
Q

Papillary layer of dermis

A

wavy surface

loose-cell rich connective tissue which fills the gaps (dermal papillae) at the deep surface of the epidermis

contains nerve endings, fibroblast, macrophages ect.

frequent capillaries

fine, not very dense collagen fibers

51
Q

ridges of papillary layer of dermis

A

dermal papillae

52
Q

reticular layer of dermis

A

deeper layer of dermis

dense and fewer cells

thick type 1 collagen fibers, often aggregate into bundles

interlacing collagen network, mostly parallel to the epidermis

53
Q

deeper layer of dermis

A

recticular layer

54
Q

reticular layer of dermis has ___ which form into bundles

A

Type 1 collagen fibers

55
Q

hypodermis

A

layer of connective tissue that anchors the dermis to the underlying bone and muscle

loose arrangment of collagen and elastin matrix

lots of adipose tissue (adipocytes) in the form of small clusters of large masses that make up a cushion of fat

56
Q

hypodermis has lots of ___ tissue that form a “cushion”

A

adipose

57
Q

loose arrangement of collagen and elastin matrix

A

hypodermis

58
Q

___ anchors the dermis to the underlying bone and muscle

A

hypodermis

59
Q

Hair follicles

A

in mammals- covers the entire body except foot pads, penis and nipples

  • flexible and keratinized structure
  • root of the hair is anchored in a tubular invagination of the epidermis, hair follicle
60
Q

the root of each hair is anchored in a tubular invagination of the epidermis called the ___

A

hair follicle

61
Q

what are some appendages of the epidermis

A

hair follicle

sebaceous gland

sweat gland

arrector pilli muscle

62
Q

label the hair follicle

A
63
Q

Hair growth stages

A

anagen (active growth)

catagen (regression)

telogen (silent/quiescence)

exogen(hair shedding)

64
Q

anagen

A

active hair growth

in mice: lasts around 3 weeks

humans: scalp hair: last several years

eyelashases/eyebrows 1-4 months

65
Q

catagen

A

regression hair growth

66
Q

telogen

A

3rd stage of hair growth

quiescence/silent

67
Q

exogen

A

4th stage of hair growth

shedding of hair

68
Q

hair growth is controlled by ___ and ___ factors

A

hormonal and hereditary

69
Q

in anagen phase of hair growth

A

stem cells get activated that move deeper into skin and trigger proliferating progenitor cells which make hair

70
Q

the bulge of the hair follicle contains the ___

A

follicular epithelial stem cells

71
Q

the bulge of the hair follicle resides in the ___ and is the deepest and most protected place within the epithelial compartment

A

base of the permanent portion of the follicle

72
Q

induction of a new anagen phase occurs when the dermal papilla recruits one or more ___

A

bulge cells

73
Q

in humans hair growth occurs in a ___ pattern

A

mosaic

each individual hair develops independently of its neighbor

74
Q

In species other than humans, hair growth occurs in a ___

A

wave pattern (mice)

cycles of growth and rest, starting at the head and move towards the tail

75
Q

__ can initiate hair growth

A

plucking- leads to apoptosis-a bunch of stuff- wave of hair growth

quorum sensing

76
Q

sinus hair follicles

A

whiskers (vibrissae)

large hairs modified to act as mechanosensors

thicker and stiffer then normal hairs

hair follicle - surrounded by blood sinus

77
Q

what am I

A
78
Q

___ amplifies the movement and allows the mechanoreceptors at the base of the vibrissa to detect extremely small deflections

A

blood

(sinus hair follicle)

(whiskers)

79
Q

___ offer an advantage to animals when use of non tactile senses is limited

A

vibrissae

(whiskers)

80
Q

Two types of sweat glands

A

eccrine (merocrine) sweat glands

apocrine sweat glands

81
Q

sebaceous glands

A

holocrine gland

empty their secretory product into the upper part of the hair follicle

found in thin skin hair follicles and lips and genitalia

alveoli

82
Q

type of gland that the secretory product is essentially the dead cells of the gland itself

an example is ___

A

holocrine

sebaceous glands

83
Q

hair follicle and its associated sebaceous gland form the ___

A

pilosebaceous unit

84
Q

What am I

A

sebaceous gland

85
Q

explain how sebaceous glands work

A

live in alveoli

basal cells are flattened and mitotically active

daughter cells accumulate lipids and grow until they break and release their contents (holocrine secretion)

86
Q

Sweat glands

A

Eccrine (merocrine) sweat glands

  • empty onto surface of epidermis
  • found in footpads of dogs and cats, nasolabial region of ruminants
  • found all over in human
  • watery secretion

-Apocrine Sweat Glands

  • non actually aprocine- misnomer
  • milk and odorless secretion
  • empties into the upper part of the hair follicle (pilosebaceous unit)
87
Q

What is this

A

eccrine sweat gland

88
Q

where are eccrine sweat glands found

A

footpads of dogs and cats, the nasolabial region of ruminants

all over in humans

89
Q

Eccrine sweat glands is a ___ duct

A

excretory - empty directly onto the surface of the skin

90
Q

A layer of ___ cells is found between the secreotory cells of the epithelium and the basement membrane in eccrine sweat glands

A

myoepithelial

91
Q

Apocrine sweat glands

A

non actually apocrine- misnomer

milk and odorless secretion

empties into the upper part of the hair follicle (pilosebaceous unit)

21 fall: histology (36 decks)

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