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BLOCK F > Histology of Skin and Dermis > Flashcards

Histology of Skin and Dermis Flashcards

1
Q

What is the importance of the skin microbiome (bacteria living on your skin)?

A

It acts as a protective barrier against pathogens by competing against them.

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2
Q

Epithelium of the skin

A

Stratified squamous epithelium (keratinized i.e. top layer is dead)

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3
Q

Skin epidermis is derived from which embryologic germ layer?

A

Ectoderm

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4
Q

3 basic layers of the integument

A

Epidermis
Dermis
Hypodermis (fatty)

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5
Q

Integument definition

A

Entire body covering, including the skin, hypodermis and appendages (hair, nails, oil and sweat glands).

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6
Q

Layers of the skin (2)

A

Epidermis (epithelium) and dermis

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7
Q

What are skin appendages (nails, hair) made of?

A

Keratinized epithelium

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8
Q

5 layers of the epidermis (top to bottom)

A
  1. stratum corneum
  2. stratum lucidum
  3. stratum granulosum
  4. stratum spinosum
  5. stratum basale or germinativum
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9
Q

Name of skin cells

A

keratinocytes

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10
Q

Specialized junctions between basement membrane and basal cells of the epidermis (cell-matrix adhesion)

A

Hemidesmosomes (using integrins)

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11
Q

Specialized junction between cells of the epidermis (cell-cell adhesion)

A

Desmosomes (using cadherins)

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12
Q

What is the name of intermediate filaments in the epidermis

A

Tonofilaments (made of keratin proteins).
These keratin filaments are found in the spiny processes of cells and insert into desmosomes.

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13
Q

What genes does the epidermis express?

A

The epidermis expresses 14 keratin genes (K1-K14) called cytokeratins.

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14
Q

Describe the cells of the stratum basale

A
  • Cuboidal cells
  • Undergo mitoses (mostly at night)
  • Replace skin epithelium within 1 month
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15
Q

Describe the appearance of stratum spinosum cells

A

Polyhedral, spiny cells (due to desmosomal connections between cells)

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16
Q

Cells of the stratum spinosum layers secrete…

A

lamellated granules (glycolipids) which prevent water loss and form a waterproof barrier in the skin

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17
Q

What type of granules are found in the keratinocytes of the stratum granulosum?
What do these granules contain?

A

Keratinocytes in this layer contain keratohyalin granules, which contain filaggrin.

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18
Q

What is the function of keratohyalin granules in the stratum granulosum?

A

The contain a protein, filaggrin, that promotes keratin filament (tonofilament) aggregation and cross-linking. Therefore, they contribute to keratinization.

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19
Q

What enzyme mediates tonofilament cross-linking in the stratum granulosum?

A

Transglutaminase

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20
Q

Is the stratum lucidum always present in the skin?

A

No, the stratum lucidum is found in thick skin only (palms, soles). It is a thin and variable layer.

Appears unstained because of its clear, featureless nature.

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21
Q

Describe the keratinocytes in the stratum lucidum (3)

A
  • The cells are dead
  • The cells have no nucleus nor organelles
  • They are densely packed with keratin tonofibrils
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22
Q

Describe the stratum corneum

A

It consists of dead, flattened keratinized cells filled with cross-linked keratin fibrils.

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23
Q

In the stratum corneum, protein deposits under the membrane create a cell envelope that forms a protective barrier. Two of these proteins are…

A

involucrin
loricrin

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24
Q

What allows the cells in the stratum corneum to detach from one another and desquamate?

A

Breakdown of desmosomal attachments

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25
In the stratum corneum, the intercellular space is filled with...
glycolipids (waterproof barrier)
26
Epidermolysis bullosa
Genetic disorders that cause fragile skin, leading to blistering and erosion in response to minor friction, trauma or pressure.
27
What is the underlying cause of epidermolysis bullosa?
Defects in the structural proteins (keratins, integrins, collagens, laminins)
28
Epidermolysis bullosa puts patients at very high risk of...
infections (loss of protective barrier)!!
29
Ichthyosis
Group of genetic disorders causing abnormal keratinization that results in dry, thickened, scaly skin (desmosomes do not break down).
30
Why is ichthyosis not a desirable disease? How does it cause infection if the skin gets thicker?
It creates pathogenic pockets where bacteria get trapped and can irritate the skin.
31
Mutations in what 2 proteins cause ichthyosis?
Filaggrin (in keratohyalin granules) Transglutaminase *AKA 2 proteins involved in keratinization*
32
Basal cell carcinoma
Skin cancer: Uncontrolled proliferation of basal keratinocytes in the epidermis. Locally invasive but rarely metastatic.
33
Squamous cell carcinoma
Skin cancer: Uncontrolled proliferation of keratinocytes in the stratum spinosum. Can breach BM and become metastatic.
34
How can the skin heal after minor burns?
Thanks to the basal cells in the hair follicles that are spared because these follicles invaginate as deep as the hypodermis. The more hair follicles a person has, the faster their skin will heal!
35
Psoriasis
Autoimmune disease causing hyper-proliferation of keratinocytes (7x) with T-cell driven inflammation. Creates thick, itchy plaques.
36
Warts
Benign viral infection of the epidermis (papilloma virus)
37
Blisters
Friction can cause mechanical separation of desmosomes, creating spaces between cell layers. Edema causes fluid buildup between those layers.
38
Name 3 non-keratinocyte epithelial cells in the epidermis
Melanocytes Langerhans cells Merkel cells
39
Describe the location and role of melanocytes.
Melanocytes sit on the basement membrane, next to basal cells. They have long processes that extend into the stratum spinosum and release granules containing melanin, which are absorbed into the cells of the stratum spinosum.
40
What is the role of melanin?
Melanin granules get absorbed into the cells of the stratum spinosum. The granules form an "umbrella" over the nucleus of these cells to protect the DNA from UV damage.
41
Mutations in tyrosinase gene causes...
albinism
42
True or false: Melanocytes have desmosomal connections to keratinocytes
FALSE: no desmosomal connections
43
Describe the process of maturation from pre-melanosomes to melanosomes
Pre-melanosomes contain tyrosine (an amino acid). They fuse with granules containing tyrosinase (an enzyme) to form melanosomes. When tyrosinase is activated by UV light, it converts tyrosine to melanin (a pigment that protects from UV damage). Melanin-filled melanosomes get absorbed by keratinocytes in the stratum spinosum.
44
2 types of melanin
Eumelanin: dark brown Pheomelanin: red, yellow
45
True or false: Albino people do not have melanocytes
False! They have melanocytes but they have gene mutations in their tyrosinase gene, so they are at increased risk of skin cancer.
46
What are Langerhans cells?
They are dendritic cells (APCs) that bind foreign antigens and migrate to lymph nodes. They are a type of immune cell.
47
What are Merkel cells?
They are mechanoreceptor cells, responsible for light touch sensation. They are connected to sensory nerve endings. Abundant in fingertips.
48
What cell contributes to the formation of connective tissue (ECM) that makes up the dermis ?
Fibroblasts
49
Where are the lymphatics and blood vessels of the skin?
In the dermis (i.e. connective issue layer of the skin: cells + ECM)
50
What is the function of the dermis?
To supply nutrients and oxygen to the avascular epidermis! It also houses immune cells and is the site of initial immune responses.
51
6 major cell types of the dermis (hint: 3 are immune cells)
1. Fibroblasts 2. Mesenchymal cells 3. Adipocytes 4. Macrophages 5. Mast cells 6. Plasma cells
52
Most abundant protein in the body
collagen
53
Collagen structure
triple helix of 3 alpha chains
54
How long does it take to make a collagen fibril?
60 min
55
Order the following in terms of diameter (small to big): microfibrils, fibres, fibrils, fascicles
Smallest to largest diameter: 1. Microfibril 2. Fibril 3. Fibre 4. Fascicle
56
What co-factor does collagen require to form its triple-helix structure?
vitamin C (ascorbic acid)
57
Vitamin C deficiency causes...
scurvy
58
Ehlers-Danlos syndrome
Caused by mutations in collagen I, III and V. Results in hyperextensive skin, hyper joint mobility and dislocation.
59
Role of lysyl oxidase
Cross-linking of collagen and elastin fibres (in dermis)
60
Marfan's syndrome
Fibrillin-1 gene mutations causing defects in elastic tissue: * aortic aneurysms * lax joints & dislocations * lens dislocation
61
Cutis laxa
Elastin and fibulin 5 mutations. Skin becomes loose, saggy and wrinkly.

BLOCK F (27 decks)

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