Lecture 3- Histology of the Skin

Question 1

Skin Functions

Answer 1

1. Protection against physical/chemical/biological attacks
2. Water barrier
3. Thermoregulation (conservation/dissipation of heat)
4. Defense barrier to microbes
5. Excretion of salt
6. Vitamin D synthesis
7. Sensory organ

Question 2

General Organization of Skin: the 3 layers

Answer 2

3 layers firmly attached to each other

1. Epidermis: outermost, from ectoderm
2. Dermis: deeper, from mesoderm
3. Hypodermis/Subcutaneous layer

Question 3

General Organization of Skin

Answer 3

Surface of palms/soles have narrow epidermal ridges separated by furrows

• each epidermal ridge corresponds to dermal papilla, are permanent/unique, create finger prints
• Dermal-epidermal junction has primary epidermal ridge, interlocks w primary dermal ridge, subdivides it into 2 secondary dermal ridges
• Some dermal papillae project upward and interlock w downward projections from epidermis (Hairless, thick skin)
• Thin skin has less and smaller dermal papillae

Question 4

Stratum Basale

Answer 4

• aka stratum germinativum
• deepest layer, single layer of cuboidal to low columnar cells on basement membrane
• Have nucleus and keep dividing to replace superficial cells

Question 5

Stratum Spinosum

Answer 5

• 2nd deepest, made of many layers of polyhedral cells that have desmosomal bridges w other cells
• contain Langherhans (combat foreign organisms) cells and processes Melanocytes (pigment producing)

Question 6

Stratum Malpighi

Answer 6

-Name for layers 1 and 2, responsible for cell renewal

Question 7

Stratum Granulosum

Answer 7

• Flat cells that contain Keratohyaline granules

* absent in thin skin`

Question 8

Stratum Lucidum

Answer 8

• Thin, transparent layer whose cells have eleidin (a transformation product of keratohyalin
• Cells lack nuclei bc are filled w keratin
• absent in thin skin

Question 9

Stratum Corneum

Answer 9

-Made of squames that are densely packed w keratin

Question 10

Keratinocytes

Answer 10

• Most predominant cell type
• All 5 layers
• produce keratin (IF protein)

Question 11

Melanocytes

Answer 11

• Melanin production
• Deplete w age, skin gets lighter, more prone to skin cancer
• neural crest

Question 12

Langerhans Cells

Answer 12

-Antigen trapping cells, interact w T cells

Question 13

Merkel Cells

Answer 13

• tactile sensations

- neural crest

Question 14

Keratin

Answer 14

-IF protein in all epithelium
-a helical, rod shaped
K5 and K14 in basal keratinocytes
K1 and K10 in stratum spinosum

Question 15

Dermis

Answer 15

• CT deep to epidermis w vessels, hair follicles, sweat glands and sensory receptors
  1. Papillary layer: superfical layer of irregular CT - Dermal ridges -Dermal papillae, capillary loops, Meissners corpuscles -Free nerve endings
  2. Reticular layer: deeper layer of denser irregular CT
• Thicker layer -Pacinian corpuscles -Ruffinis corpuscles

Question 16

Blood Supply to Skin

Answer 16

• Role in nutrient supply and thermoregulation
  1. Cutaneous Plexus: arteries and veins found at dermo-hypodermal junction
  2. Sub-papillary plexus: located in papillary layer of dermis, capillary loops extend into papila and result in convective heat loss/epidermis nutrient supply
  3. AV shunts: between 1 and 2. Supplied by sympathetic nerves, restrict flow through superficial plexus to reduce heat loss in extreme cod

Question 17

Epidermis vs Dermis

Answer 17

Epidermis: -highly cellular -little ECM -avascular
Dermis: -predominantly ECM
-low proportion of cells
-highly vascularized

Question 18

Sensory Receptors

Answer 18

Meissner Corpuscles: Dermal papila, tactile receptor
Merkel Cell: Basal layer of epidermis, tactile receptor
Free nerve endings: no myelin or schwann cells, pain and temp
Ruffini end organs: in skin and joint capsule, stretching
Pacinian corpuscle: hypodermis and deep fascia,, pressure
Peritrichial nerve ending: base of hair follicle, hair movement

Question 19

Hair

Answer 19

• Composed of shaft of cornified cells and a root contained w in hair follicle
• associated w sebaceous gland, called pilosebaceous unit
• Arrector pili muscle attaches to hair follicle

Question 20

Hair growth

Answer 20

Anagen: Growth period, 80% of hair in anagen phase
Catagen: brief period of follicle regression or involution, 3 weeks
Telogen: inactive phase, 14%

Question 21

Sweat Glands

Answer 21

• Simple, coiled, tubular glands
• produce sweat delivered to surface via long ducts
• secretory portions surrounded by myoepithelial cells

Question 22

Sebaceous Gland

Answer 22

• Branched, acinar, holocrine glands
• produce oily secretion (sebum)
• secretion delivered into lumen of hair follicle

Question 23

Epidermolyis Bullosa Simplex

Answer 23

• Mutated K5 & K14 (affacts basal keratinocytes)
• weak keratin filaments
• blisters in area of trauma
• mild

Question 24

Epidermolytic Hyperkeratosis

Answer 24

• Mutated K10
• keratinocytes in spinosum/granulosum lyse in response to trauma
• thick,scaly skin, blisters

Question 25

Psoriasis

Answer 25

- Increase in proliferating cells - decreased mitotic cycle time (7days instead of 20-30) - causes epidermal thickness = thick scaly skin

Question 26

Ichthyoses

Answer 26

-hereditary -thickening of corneum Due to: 1. increased cohesiveness of corneum 2. defective keratinization from keratin gene mutations 3. increased mitotic activity in basal keratinocytes

Question 27

Malignant Melanoma

Answer 27

-Skin cancer that stems from melanocytes (in basal layer of epidermis) Mole: benign cluster of melanocytes, can become malignant and are then melanoma -most virulent skin cancer

Question 28

Squamous Cell Carcinoma

Answer 28

- Dermal invasion by abnormal cells of epidermis - pleomorphism (different cells at different stages) of tumor cells - kerartinization w/in cells = pink cytoplasm

Question 29

Bullous Pemphigoid

Answer 29

- Blister formation | - auto-immune response against proteins associated w desmosomes/ hemi-desmosomes

Question 30

Junctional Epidermolysis Bullosa

Answer 30

- Blisters at epidermal basal lamina - mild to severe, fatal by 2 - due to gene mutations for structural proteins

Question 31

Acne Vulgaris

Answer 31

- inflammatory disorder of pilosebaceous unit - excessive keratinization w/in the unit causes excessive sebum production = blockage of ducts in follicle - anaerobic bacteria grow in accumulated sebum = localized inflammation/neutrophil infiltration