Integument

Question 1

Layers of Skin

Answer 1

• Epidermis
  
  • Outer epithelial layer of skin, consisting of keratinized stratified squamous epithelium
  • Contains keratinocytes, melanocytes, Langerhans cells, Merkel cells
  • Functions in protection from wear/tear, dessication, water uptake, pathogens, UV
• Dermis
  
  • Connective tissue layer that underlies and supports epidermis
  • Divided into two layers:
    
    • Papillary layer contains loose CT
    • Reticular layer contains dense CT
• Hypodermis (Subcutaneous layer)
  
  • Consists of adipose tissue separated by paritions of loose CT, hair follicle bases, sweat glands, arrector pili, etc.
  • Connects dermis to underlying tissues and structures
  • Functions in energy storage and insulation against heat loss

Question 2

Stratum germinativum

Answer 2

• Deepest layer of cells, one-cell layer thick
• All cells in contact with basement membrane
  
  • Attached via hemidesmosomes
  • Anchoring filaments extend into basal lamina
• Contains stem cell population capable of dividing to produce new skin cells

Question 3

Stratum spinosum

Answer 3

• Layer of epidermis between stratum germinativum and stratum granulosum
• Consists of several layers of large, polyhedral keratinocytes
• Shrinkage during tissue preparation creates “spines”
  
  • Mark location of desmosome attachment to other keratinocytes

Question 4

Stratum granulosum

Answer 4

• Layer of epidermis superficial to stratum spinosum
• Consists of one to several layers of flattened keratinocytes that are beginning to synthesize keratin
  
  • Contain basophilic keratohyaline granules

Question 5

Stratum lucidum

Answer 5

• Layer of flat, refractile cells that often appears as bright (clear to pink) or unstained line
• Found only in thick skin
• Contain partially keratinized cells that may lack nuclei

Question 6

Stratum corneum

Answer 6

• Multiple layers of very flat, anucleated cells filled with keratin
• Deep cells coated with glycolipid to create water proof barrier

Question 7

Papillary Layer

Answer 7

• Thinner, superficial layer of dermis (encompasses dermal papilla and ridges)
• Dermal papilla increase surface area to strengthen attachment to epidermis and facilitate diffusion of nutrients/wastes between the two layers
• Consists of loose CT:
  
  • Thin fibers of collagen type I and III
  • Elastic fibers
  • Anchoring fibrils
• Contains blood vessels, nerves, and higher cell density

Question 8

Reticular Layer

Answer 8

• Thicker, deeper layer of dermis consisting of dense irregular CT:
  
  • Bundles of type I collagen fibers
  • Elastic fibers
• Contain lower density of cells and may contain smooth MM in certain locations (e.g. areolae of breast, penis, scrotum, perineum)

Question 9

Keratinocyte

Answer 9

• Principal cell type of epidermis derived from stem cells of stratum germinativum
• Produce soft keratin
  
  • Keratin filaments crosslinked by intermediate-filament associated proteins (filaggrin and trichohyalin) released from keratohyalin granules
• Produce glycolipids
  
  • Secreted into extracellular space between stratum granulosum and corneum to form lipid envelop that acts as water barrier (prevents water uptake and dessication)
• Form squames
  
  • Flat, anucleate cells with thickened plasma membranes filled with keratin
  • Slough off from skin surface

Question 10

Melanocyte

Answer 10

• Non-epithelial, dendritic, pigment-producing cells of skin, derived from neural crest cells
• Located in stratum germinativum of epidermis; processes extend into stratum spinosum
• Produce melanin pigment
  
  • Keratinocytes phagocytose tips of melanocyte processes containing melanin-filled vescicles (melanosomes)
  • Melanin granules retained as keratinocytes differentiate and migrate to skin surface

Question 11

Langerhans Cell

Answer 11

• Non-epithelial, dendritic cell located in stratum spinosum of epidermis (Not differentiable with H&E)
• Functions as part of body-wide mononuclear phagocytic system
  
  • Phagocytose/process antigens and present to T cells to initiate contact hypersensitivity reactions
• Origin: embryonic mesenchyme; derived from stem cells in bone marrow

Question 12

Merkel Cell

Answer 12

• Modified epidermal cell located in stratum basale, attached to keratinocytes by desmosomes
• Associated with terminal bulb of afferent nerve fiber to function as touch receptor (Merkel’s corpuscle)
  
  • Concentrated in acute sensory perception sites (e.g. fingertips)

Question 13

Free Nerve Endings

Answer 13

• Most numerous type of nerve ending
• Terminate in stratum granulosum of epidermis in associatio with hair follicles
  
  • Act as mechanoreceptors

Question 14

Pacinian Corpuscle

Answer 14

• Encapsulated nerve ending that acts as a pressure receptor
• Located in dermis, hypodermis, internal organs, etc.
• Large, ovoid shaped structure (onion-like appearance in c.s.) consisting of:
  
  • Unmyelinated nerve fiber ending
  • Inner core of Schwann cells
  • Outer core of concentric lamellae

Question 15

Meissner’s Corpuscle

Answer 15

• Touch receptor located in dermal papillae of dermis of skin
• Consists of 1-2 unmyelinated nerve fiber endings in capsule of Schwann cells

Question 16

Arrector Pili

Answer 16

• Band of smooth MM anchored in upper layer of dermis and attached to CT sheath of hair follicle
• Contraction pulls on follicle, causing hair to become erect
  
  • Modulate insulation by varying thickness of hair layer (animals)
  • “Goose bumps” (humans)