Histology: Skin

Question 1

Integumentary System

Answer 1

Skin

Epidermial Appendages

• Hair/Hair follicles
• Sweat glands
• Sebaceous glands
• Nails
• Mammary Glands

Question 2

Functions of Skin

Answer 2

• Barrier
• Immunologic: APCs to prevent from foregin
• Homeostasis: body temperature and water loss
• Sensation
• Endocrine: converts vitamin D to active form
• Excretion
• Absorption: lipid-soluble drugs

Question 3

Layers of Skin

Answer 3

Epidermis

• Ketarinized straftified squamous epithelium
• Avascular

Dermis

• Proviees mechanical support/strength
• Thickness of skin

Hypodermis

• Adipose tissue deep to dermis
• NOT part of skin

Question 4

Thick vs. Thin Skin

Answer 4

Thick Skin

• Palms of hands/soles of feet
• Hairless
• Thick epidermis

Thin Skin

• Thin epidermis
• Hair follicles

Question 5

Layers of Epidermis

Answer 5

• Stratum Basale (stratum germinativum)
• Stratum Spinosum
• Stratum Granulosum
• Stratum Lucidum (thick skin only)
• Stratum Corneum

Deep to superficial

Question 6

Stratum Basale

Answer 6

• Single layer of basophilic cells
• Cuboidal to low columnar
• Attached to basal lamina by hemidesmosomes
• Mitotically active stem cells
  
  • Gives rise to cells in upper layers

Question 7

Stratum Spinosum

Answer 7

• Several layers thick
• Cytoplasmis processes appear as tiny spines
  
  • Desmosomes
• Cells migrate upward through SS
  
  • Cells become more flat as they travel superiorly

Question 8

Stratum Granulosum

Answer 8

• Contains basophilic keratohyalin granules (contain filagren)
• Most superficial non-keratinized layer
• Squamous cells, 1-3 layers thick

Question 9

Stratum Lucidum

Answer 9

• Only in thick skin
• Translucent
• Highly keratinized obscures nucleus

Question 10

Stratum Corneum

Answer 10

• Varies the most in thickness
• Anucleated, squamous cells
• Filled with keratin filaments
  
  • Water barrier
• Surface cells shed via desquamation

Question 11

Keratinocytes

Answer 11

• Majority of cells
• Produce keratin
  
  • Form epidermal water barrier

Keratinization (2-6 hours):

• Begins in stratum granulosum
  
  • Keratohylain granules secretes fillegrin
  • Keratin filaments aggregate into tonofibrils
• Nucleus and organelles break down
• Plasma membrane thickens

Question 12

Epidermal Water Barrier

Answer 12

2 elements:

• Cell envelope (inside plasma membrane)
• Lipid envelope (intercellular spaces)
  
  • Lamellar bodies (filled with lipids)
    
    • Secreted in stratum granulosum

Question 13

Melanocytes

Answer 13

• Come from neural crest cells
• Located in stratum basale
• Produce melanin (pigment that protects skin from UV)
• Are dendritic cells: deposit melanin into keratinocytes via dendritic processes

Question 14

Melanin Synthesis

Answer 14

Synthesized from tyrosine –> DOPA –> Melanin

• Melanosomes are small, dark-staining granules that are transferred to keratinocytes via cytocrine secretion

Question 15

Albinism

Answer 15

• Results from defect in tyrosinase (converts tyrosine to DOPA)

Question 16

Malignant Melanoma

Answer 16

• Skin cancer that develops from melanocytes
• Caused by UV exposure
• ABCDE rule (asymmetry, border, color, diameter, evolving)

Question 17

Langerhans’ Cells

Answer 17

APC cells in skin

• Derived from monocytes
• Most abundant in stratum spinosum
• Do not show up with H&E stain

Question 18

Merkel/Tactile Cells

Answer 18

• Function as mechanoreceptors
• Located in statum basale
  
  • Closely associated with sensory nerve fibers
    
    • Merkel’s Corpuscles (light touch)
• Merkel Cell Carcinomas
  
  • Very aggressive

Question 19

Dermis

Answer 19

• Papillary Layer
  
  • ​Loose CT deep to epidermis
  • Type I and III collagen; Elastic Fibers
  • Dermal papilla
• Reticular Layer
  
  • Dense irregular CT
  • Type I collagen
  • Large blood vessels/nerves
  • Langer’s Lines: some arrangment of collagen (heals more easily)

Question 20

Nerve Supply

Answer 20

Free Nerve Endings

• Fine touch, heat, cold
• Surround hair follicles

Encapsulated Receptors

Question 21

Pcainian Corpuscles

Answer 21

• Deep pressure and vibration
• Located in dermis/hypodermis
• Myelinated nerve fiber surrounded by concentric lamellae

Question 22

Meissner’s Corpuscles

Answer 22

• Sensitive to light touch
• Abundant in thick/hairless skin
• In dermal papillae
  
  • Cylindrical shape

Question 23

Ruffini Corpuscles

Answer 23

• Stretch and twisting (torque)
• Deep in dermis
• Elongated fusiform shape

Question 24

Hair

Answer 24

• Keratinized epithelial cells, form within hair follicle
• Shaft (above surface of skin)
  
  • ​Medulla
  • Cortex (color and texture)
  • Cuticle
• Root (below skin)
• Bulb
  
  • ​Dermis projects to hair bulb (dermal papilla)
  • Hair matrix

Question 25

Hair Follicle

Answer 25

**Epithelial Root Sheath** * Continuous with epidermis * Two Layers: * **Internal Root Sheath** * **External Root Sheath** **Connective Tissue Root Sheath** * Continuous with dermis **Arrector Pili Muscles** * Smooth muscles

Question 26

Sebacous Gland

Answer 26

* Branched acinar glands * Basal layer of progenitor cells with inner **sebocytes** * Outgrowth of **external root sheath** * Produce **sebum** * **Holocrine Secretion** * Entire cell breaks down

Question 27

Sweat Glands

Answer 27

**Eccrine** **Apocrine** * Axilla, Areola, Genital * Associated with hair follicles

Question 28

Eccrine Sweat Glands

Answer 28

* Simple, coiled tubular glands * Downgrowth of epidermis * NOT associated with hair follicles * **Temperature Regulation** * Sympathetic Nervous System * **Cholinergic Transmitters** Secretory Portion: * Clear Cells: produce watery component of sweat * Dark Cells: glycoprotein production * Myoepithelial cells: contracticle cells Duct Segment: * Stratified cuboidal epithelium

Question 29

Apocrine Sweat Glands

Answer 29

* Coiled Tubular Glands * Develop from **hair follicles** * **Merocrine secretion** * Sympathetic nervous system * **Adrenergic transmitters**