Chapter 6: Integumentary System Layers: Epidermis and Dermis; Lines of Cleavage

What is the integumentary system?

• skin

• covers body and accessary tissues (nails, hair, sweat glands, sebaceous glands)

• cutaneous membrane, barrier to the outside world (first line of defense)

• visual indicator of our physiology and health

What are the layers of the integument?

• epidermis: stratified squamous epithelium

• dermis: deeper (reticular) layer; primarily dense irregular connective tissue

• subcutaneous layer (hypodermis): deep to dermis, layer of alveolar and CT, not part of integumentary system

What is the epidermis?

• epithelium of the integument

• keratinized

• stratified squamous epithelium

• First three layers composed of living keratinocytes

• consists of stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, stratum corneum

What are the layers of the epidmeris?

• deep to superficial

  • stratum basale

  • stratum spinosum

  • stratum granulosum

  • stratum lucidum

  • stratum corneum

What is the stratum basale of the epidermis?

• deepest epidermal layer,

• single layer of cuboidal to low columnar cells

• three types of cells

  • keratinocytes

  • melanocytes

  • tactile

What are the keratinocytes of the stratum basale layer?

• Found in all layers

• those in stratum basale are large stem cells

  • divide to regenerate new cells

• synthesize keratin

  • a protein that strengthens epidermis

What are the melanocytes of the stratum basale layer?

• produce and store pigment (melanin) in response to ultraviolet light,

• transfer pigment granules (melanosomes) into keratinocytes,

• shield nuclear DNA from UV radiation

• Scattered among keratinocytes in stratum basale

What are the tactile cells of the stratum basale?

• Merkel cells, few in number

• sensitive to touch, when compressed,

• release chemicals, stimulate sensory nerve endings

What is the stratum spinosum?

• Several layers of polygonal keratinocytes

• new cells from stratum basale pushed into this layer

• nondividing keratinocytes attached by desmosomes

• epidermal dendritic cells (Langerhans cells)

What is the stratum granulosum?

• 3 to 5 layers of keratinocytes that begin to fill with keratin

• nucleus and organelles to disintegrate

• cells are dead

What are epidermal dendritic cells?

• initiate immune response

• found un spinosum and granulosum

What is the stratum lucidum?

• translucent layer

• 2 to 3 cell layers thick

• found only on thick skin on palms and soles

What is the stratum corneum?

• superficial stratum composed of 20 to 30 layers of dead interlocking, anucleate (lacking a nucleus), keratinized cells, dry,

• thickened surface is protective against abrasion and infection

What is the dermis?

• Deep to epidermis

• composed of CT proper

• other structures present: blood vessels, sweat glands, sebaceous glands, hair follicles, nail roots, sensory nerve endings, arrector pili, motile dendritic cells

What are the layers of the dermis?

• papillary

• reticular

What is the papillary layer of the dermis?

• superficial region of dermis (named for projections of dermis; dermal papillae)

• deep to epidermis

• areolar connective tissue

• interlock with epidermal ridges to increase area of contact between layers

What is the reticular layer of the dermis?

• deeper

• major portion of dermis

• dense irregular connective tissue

What is the subcutaneous layer?

• hypodermis, superficial fascia

• Not part of integument, areolar and adipose CT

• protection, energy storage, and insulation, common drug injection site, extensive vascular network promotes rapid absorption, thickness/distribution influenced by sex hormones

What are lines of cleavage?

• collagen and elastic fibers oriented in parallel bundles at specific locations

• Bundles function to resist stress during routine movement

What is the orientation indicated by lines of cleavage?

• incisions parallel to cleavage lines more likely to heal quickly

• incisions perpendicular to cleavage lines are more likely to open due to cut elastic fibers

What causes stretch marks?

• skin is stretched beyond its capabilities, results in striae

• some collagen fibers torn