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LOCO 2 > Introduction to Skin > Flashcards

Introduction to Skin Flashcards

1
Q

The skin is the largest organ in the body. What % of total body weight does it make up?

A

12-15%

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2
Q

How many cells are in the skin?

A

1.6 trillion

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3
Q

How often to people visit the GP due to skin problems?

A

Most common reason for visiting a GP (42%)

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4
Q

Give some examples of skin diseases. (4)

A 
Malignant melanoma (cancer)
Psoriasis (inflammation)
Diabetic ulcer (trauma)
Epidermolysis bullosa (genetic)
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5
Q

What is the function of the skin? (4)

A

Protection
Insulation
Provides sensory information
Vitamin D synthesis

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6
Q

What does the skin protect from? (5)

A 
Physical trauma
Infection
Penetration of drugs and chemicals
UV radiation
Water loss
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7
Q

What are the layers of the skin?

A

Epidermis
Dermis
(May classify adipose tissue as a third layer = hypodermis)

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8
Q

What type of epithelium is the epidermis?

A

Stratified squamous

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9
Q

What is the major cell type of the epidermis?

A

Keratinocyte

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10
Q

What are the four main layers of the epidermis?

A 
Stratum basale (basal layer)
Stratum spinosum (spinous layer)
Stratum granulosum (granular layer)
Stratum corneum (cornified layer)
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11
Q

What does the epidermis also include?

A

Hair and sebaceous gland

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12
Q

Describe the appearance of the basal cells of the epidermis.

A

Basal cells are compact and have dark nuclei

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13
Q

Describe the appearance of the stratum spinosum cells of the epidermis.

A

Spiny processes. Separate keratinocytes. Larger cells.

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14
Q

Describe the appearance of the granular layer cells of the epidermis.

A

Contains purple keratinohyaline granules. Start to lose nuclei.

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15
Q

Describe the appearance of the stratum corneum cells of the epidermis.

A

The cells are flattened and have no nuclei.

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16
Q

What cell type are keratinocytes? What do they produce?

A

Epithelial cell

Keratins (to make dense network of cytoskeleton to provide strength and integrity)

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17
Q

Keratins are _______ filaments. They are the most abundant proteins in _______, ____ and _____.

A

Intermediate

Stratum corneum, hair and nails

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18
Q

How many subtypes of keratins are there?

A

54

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19
Q

What are the two main types of keratins? What defines the difference in the two?

A

Soft (alpha type) and hard (beta type)
The difference is defined by the secondary structure and S-S bonding – soft keratins are formed from alpha helix/coils and hard keratins are formed from beta sheets.

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20
Q

What is the molecular weight of keratins?

A

40-50,0000 kD

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21
Q

Keratins always expressed as a pair – what are these pairs?

A

Acidic and basic pairs (to maintain neutral charge)

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22
Q

What is the expression pattern of keratins specific to?

A

Epidermal layer

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23
Q

Where does proliferation occur?

A

In basal layer
The cells once committed to differentiate, being upward migration and terminal differentiation. They are moved up and eventually shed from the surface.

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24
Q

What maintains the epidermis? Describe these.

A

Population of adult stem cells

Long lived, slow cycling, capable of self-renewal and terminal differentiation

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25
Q

What do basal cells adhere to?

A

ECM rich basement membrane

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26
Q

What does the basement membrane consist of?

A

Laminin 332, Collagen IV, and Collagen VII

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27
Q

What do hemidesmosomes do?

A

They are integrin receptors that link keratin cytoskeleton to the basement membrane

28
Q

What is the role of the basement membrane? (3)

A

Essential for cell polarity, regulating basal cell function, and anchoring epidermis to dermis

29
Q

Describe the stratum spinosum.

A 
3-4 cell layers thick
Numerous desmosomes (structures holding cell together) give cells a spiny appearance
30
Q

Describe the stratum granulosum.

A

2-3 cell layers

Characterised by large granules of keratohyalin

31
Q

Give three examples of keratohyalin proteins.

A

Filaggrin, involucrin, loricrin

32
Q

Describe the stratum corneum.

A

A thick cornified envelope, cross-linked by enzymes, that acts as the main protective barrier of the skin. These cells are dead and contain large amounts of intracellular lipids (ceramides) to maintain moisture/prevent dehydration.

33
Q

Name four types of cell-cell adhesions present in skin.

A

Adherens junctions, desmosomes, tight junctions, gap junctions

34
Q

What is an adherens junction? How does this differ from a desmosome?

A

Cadherin receptor linked to actin cytoskeleton. It links cells to one another and is linked with cytoskeleton to provide mechanical integrity and strength.
A desmosome links to KERATIN cytoskeleton, rather than actin.

35
Q

What are tight junctions?

A

Claudin and occludin seal intercellular space (space between cells) so nothing can pass between them

36
Q

What are gap junctions?

A

Intercellular pores (within the cell membrane) made up of connexins. They link cells to each other so they can communicate.

37
Q

What are the three layers of the dermis?

A

Papillary, reticular, adipose

38
Q

What is the dermis made up of? What is its role?

A

Complex mix of macromolecules (mainly ECM), with a few cells interspersed. It is vascularised and innervated.
Provides strength and elasticity to skin

39
Q

What is the main cell type in the dermis?

A

Fibroblast

40
Q

What is the developmental origin of fibroblasts? What do they do?

A

Mesenchymal origin

Synthesise collagen, elastin and proteoglycans (i.e. they produce ECM)

41
Q

Where is the papillary layer?

A

Directly beneath epidermis and basement membrane

42
Q

What does the papillary layer contain?

A

Many blood capillaries

Fine, randomly oriented collagen (type III), and elastin – this makes it elastic and deformable

43
Q

Describe the reticular layer.

A

It has large and densely packed collagen fibres, so has more strength and rigidity.
It provides much of the mechanical strength of the skin.

44
Q

Name skin glands and appendages. (3)

A

Pilosebaceous unit (hair follicle, sebaceous gland)
Eccrine sweat gland
Apocrine gland

45
Q

Where are hair follicles found? What are they part of?

A

Over entire body. They are part of the epidermis.

46
Q

What are the two types of hair follicle?

A

Vellus (body hair)

Terminal (scalp and secondary sexual hair)

47
Q

What cells produce hair?

What cells control hair growth?

A

Matrix keratinocytes

Dermal papilla fibroblasts

48
Q

Where are hair follicle stem cells localised to? What do they express?

A

Bulge region

Keratin 15

49
Q

What do HF stem cells do?

A

They are slow cycling cells that give rise to hair cells (under normal conditions). They contribute to SG and epidermis upon wounding.

50
Q

Hair growth is cyclical. What are the three main phases?

A

Anagen (active), catagen (regressive), and telogen (resting)

51
Q

What type of gland are sebaceous glands? What do they respond to, and so when do they enlarge?

A

Exocrine

Androgen-sensitive, enlarge at puberty

52
Q

What do mature sebocytes contain? How is it released?

A

Sebum – the cell ruptures and sebum is release into sebaceous duct and onto skin

53
Q

What does infection of sebaceous glands cause?

A

Acne

54
Q

What are eccrine sweat glands for? What are the two main components?

A

Thermoregulation

Excretory duct and secretory coil

55
Q

What is a apocrine gland? What do they release?

A

Sweat gland associated with hair follicles e.g. in axilla and pubic region
Their secretion is odourless. It is broken down on skin by bacteria. Release volatile fatty acids.

56
Q

What type of cells are melanocytes (and also Langerhan cells)? Where do they sit?

A

Dendritic cells

Sits in epidermis on basement membrane and hair matrix.

57
Q

What do melanocytes produce?

A

Melanin in melanosomes (eumelanin and pheomelanin). Melanosomes are injected into keratinocytes to give skin pigmentation and protect against UV radiation.

58
Q

Where are Langerhan cells found? What do they do?

A

Basal and spinous layers

Antigen presenting cell/first line of defence – detects antigens and presents them to T lymphocytes

59
Q

Where are Merkel cells found? What are they for?

A 
Stratum basale
Sensory perception (light touch)
60
Q

Where are Mast cells found? What do they do?

A

Dermis

Secretes histamine in response to allergen

61
Q

What are the three types of wounds?

A

Superficial – epidermis
Partial thickness – epidermis and dermis
Full thickness – epidermis, dermis, hypodermis

62
Q

What are the three phases of wound healing?

A

Inflammation
Proliferation
Maturation

63
Q

Describe the inflammation phase of wound healing.

A
  • A fibrin blood clot forms and immune cells arrive.
  • It can last from minutes to a few days.
  • Action of platelets, endothelial cells and immune components. Attach pathogens and seal off the wound. -Regulated by wide range of growth factors and cytokines e.g. IL-1.
64
Q

Describe the proliferation phase of wound healing.

A
  • Proliferation of keratinocytes (migrate over the wound to restore barrier function)
  • Infiltration of fibroblasts to produce ECM
  • Done in haphazard way
  • Endothelial cells help repair damaged blood vessels
  • Regulated by wide range of growth factors and cytokines AND anabolic growth factors (e.g. TGF-beta)
65
Q

Describe the maturation phase of wound healing.

A
  • Quickly deposited tissue is broken down and remodelled into normal skin structure
  • Regulated by some of the same growth factors and cytokines as the other phases
66
Q

Name three potential complications of wounds/healing.

A
  1. Infection
  2. Chronic wounds (not healed >6 wks) - e.g. venous, pressure, diabetic ulcer
  3. Scarring (e.g. keloid scar)

LOCO 2 (28 decks)

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