5. Skin Histology

Question 1

1. Identify and describe the characteristic histological and cytological features of cells from skin (objective)

Answer 1

Answer later

Question 2

2. Describe the physiological roles of different cell types from the skin (objective)

Answer 2

Answer later

Question 3

Protective Function of Skin

Answer 3

• Physical barrier against thermal and mechanical insults and most potential pathogens
• Dark pigment melanin in epidermis protects cell nuclei from UV radiation
• Permeability barrier against excessive loss or uptake of water
• Selective permeability of some lipophillic drugs

Question 4

Sensory Function of Skin

Answer 4

• Sensory receptors allow skin to constantly monitor the environment
• Various skin mechanoreceptors help regular body’s interactions with physical objects

Question 5

Thermoregulatory Function of Skin

Answer 5

• Constant body temperature is normally easily maintained thanks to skin’s insulating components (ie fatty layer and hair on the head)
• Mechanisms for accelerating heat loss (sweat production and a dense superficial microvasculature), especially with fatty tissue

Question 6

Metabolic Function of Skin

Answer 6

• Cells of skin synthesize vitamin D3, needed in calcium metabolism and proper bone formation, through local action of UV light on the vitamin’s precursor
• Excess electrolytes can be removed in sweat, and the subcutaneous layer stores a significant amount of energy in the form of fat

Question 7

Other General Properties of Skin

Answer 7

• Elasticity

- Self-renewing throughout life (injured skin is repaired rapidly)

Question 8

General Layers of Skin

Answer 8

Epidermis, Dermis (papillary and reticular layer), Subcutaneous Layer

Question 9

Epidermis (general)

Answer 9

• Forms major distinction between thick skin (palms and soles, 400-1400um) and thin skin (75-150um)
• Lacks microvasculature but receives nutrients and oxygen by diffusion from dermis

Question 10

Epidermis is a stratified squamous keratinized epithelium

Answer 10

Cellular component:
-epithelial cells are called keratinocytes (squamous cells)
-pigment producing melanocytes
-antigen-presenting Langerhans cells
-Tactile Merkel cells
Layers:
-stratum basale, spinosum, granulosum, lucidum, corneum

Question 11

Stratum Basale

Answer 11

• Intense mitotic activity and contains (along with deepest part of next layer) all progenitor cells for all epidermal layers
• Single layer of basophilic cuboidal or columnar cells on the basement membrane at dermal-epidermal junction
• Hemidesmosomes in basal cell membranes join these cells to the basal lamina
• Desmosomes bind cells together in their lateral and upper surfaces
• During differentiation cells move upward

Question 12

Stratum Spinosum

Answer 12

• Just above basal layer
• Thickest layer, especially in epidermal ridges
• Consists of generally polyhedral cells with central nuclei
• Desmosomes holding cell layers together
• Thick skin subject to continuous friction and pressure (such as foot soles) has a thicker stratum spinosum
• Most basal layer can repair

Question 13

Stratum Granulosum

Answer 13

• 3-5 layers of flattened cells, undergoing terminal differentiation process of keratinization
• Cytoplasm is filled with intensely basophilic masses (called keratohyaline granules and lamellar granules)
• Lamellar granules undergo exocytosis, producing lipid-rich impermeable layer around the cells

Question 14

Stratum Lucidum

Answer 14

• Only in thick skin
• Consists of a thin, translucent layer of flattened eosinophilic keratinocytes held together by desmosomes
• Nuclei and organelles have been lost
• Cytoplasm consists almost exclusively of packed keratin filaments

Question 15

Stratum Corneum

Answer 15

• 15-20 layers of squamous, keratinized cells
• By end of keratinization, the cells only contain amorphous fibrillar proteins with plasma membranes surrounded by lipid-rich layer
• These fully keratinized or cornified cells called squames are continuously shed at epidermal surface as desmosomes and lipid-rich envelopes break down

Question 16

Squamous Cell Carcinoma

Answer 16

Stratum Spinosum (keratinocytes)

Question 17

Basal Cell Carcinoma

Answer 17

Stratum Basale (basal cells)

Question 18

Melanoma

Answer 18

Stratum Basale (melanocytes)

Question 19

Merkel Cell Carcinoma

Answer 19

Stratum Basale (Merkel Cells)

Question 20

Friction Blisters

Answer 20

Fluid build-up between epidermis and dermis

Question 21

Hypopigmentation (Albinism)

Answer 21

Congenital defect in melanin-producing pathway (defect in tyrosinase; tyrosine to dopa blocked)

Pathway ends in two pigments (pheomelanins and eumelanins)

Question 22

Skin Pigments

Answer 22

• Eumelanins are brown or black pigments produced by melanocyte
• Pheomelanin in red hair

Question 23

Depigmentation (Vitiligo)

Answer 23

Acquired condition with loss or decreased activity of melanocytes

Question 24

Dermis

Answer 24

Connective tissue that supports epidermis and binds subcutaneous tissue

Question 25

Dermis (cellular component)

Answer 25

- Fibroblasts - Macrophages - Mast cells - Other leukocytes

Question 26

Dermis (non-cellular component)

Answer 26

- Collagen (Type 1 and 3) | - Elastic fibers (elastin)

Question 27

Dermis (layers)

Answer 27

- Papillary layer (loose connective tissue) | - Reticular layer (dense irregular connective tissue)

Question 28

Dermatofibroma

Answer 28

Fibroblasts/dendritic cells | -Non-malignant version

Question 29

Dermatofibrosarcoma Proteburans

Answer 29

Fibroblasts | -Malignant version

Question 30

Hemangioma

Answer 30

``` Endothelial cells (vessels) -Non-malignant version ```

Question 31

Hemangiosarcoma

Answer 31

``` Endothelial cells (vessels) -Malignant version ```

Question 32

Wound Healing

Answer 32

Time depends on size, medical condition, need vitamin C, different responses depending how deep 1. Cut blood vessels bleed into the wound 2. Blood clot forms and leukocytes clean wound 3. Blood vessels regrow and granulation tissue forms 4. Epithelium regenerates and connective tissue fibrosis occurs (scar tissue)

Question 33

Skin Summary 1/3

Answer 33

Functional tissue is stratified squamous keratinized epithelium (epidermis) Composed of highly specialized squamous cells called keratinocytes -Tightly bound to other cells (tight and adherent junctions, desmosomes) and to basement membrane (hemidesmosomes) -Specialized functions: lamellar granules in stratum granulosum extrude lipid-rich material to form lipid barrier; stacks of flattened plates form protective acellular layer (stratum corneum)

Question 34

Skin Summary 2/3

Answer 34

Stroma of skin is composed of dermis (supports and nourishes epithelial layer) and hypodermis (loose connective tissue that attaches dermis to underlying tissues)

Question 35

Skin Summary 3/3

Answer 35

Skin epithelium also shows folds, analogous to GI epithelium of small bowel, but in this case the folds are at basal surface and are to increase adhesive area rather than absorptive area -Epidermal (rete) ridges and dermal papillae