Anatomy of Integ System

• integumentary system is composed of:

  • epidermis
  • dermis
  • dermal-epidermal junction (basement membrane)
  • subcutaneous tissue
• epidermis:

  • stratified epithelium ranges from 0.06-0.6 mm in thickness
  • cellular + avascular
  • ~90% keratinocytes
  • undergoes continual renewal with shedding from outer layer + renewal from within
  • depends on dermis for nutrition
• keratinocytes:

  • create keratin
  • keratin: fibrous proteins which are resistant to enzymatic digestion
• functions of epidermis:

  • fluid retention
  • protection from irritants + friction
  • synthesis of vitamin D
  • pigmentation
  • provides light touch sensation
• 5 layers of epidermis:

  • stratum corneum
  • stratum lucidum
  • stratum granulosum
  • stratum spinosum
  • stratum basal
• stratum corneum (outermost layer of epidermis):

  • dead kertinized cells
  • continually shed
  • replaced by next lower level
  • thickest layer + accounts for up to 3/4 epidermal thickness
• stratum lucidum:

  • layer of dead keratinocytes that replace stratum corneum
  • found only on soles, palms, + fingertips
• stratum granulosum:

  • granular layer
  • 3-5 cellular layers thick
• stratum spinosum:

  • wide, multisided cells that flatten as they migrage out to stratum corneum
  • contains Langerhans cells for immunity
• stratum basal:

  • active layer of keratinocytes that divide + differentiate
  • melanocytes regenerate
  • rete ridges protrude downward
• cellular migration from basal layer to corneum takes 14-21 days
• epidermal key cells:

  • keratinocytes
  • melanocytes
  • merkel cells
  • langerhans cells
• merkel cells: light touch receptors (basal layer)
• langerhans cells: derived from bone marrow + provide immunity
• epidermal appendages:

  • hair: insulates the body; each follicle has a sebaceous gland
  • sebaceous glands: secret sebum for lubrication
  • sudoriferous glands: produce sweat + are present everywhere but lips + ears
  • nails: hard keratin
• basement membrane (basement membrane zone):

  • separates epidermis from dermis
  • contains rete ridges
  • reach down from epidermis into papillary layer of dermis
  • ridge height decreases with age
  • important for skin integrity (partial reason for skin tears with age)
• dermis:

  • thickest layer of skin at 2-4 mm thick
  • consists of 2 dermal layers
  • vascular + innervated
  • contains collagen + elastin
• collagen:

  • type 1 proteins
  • 77-85% of collagen protein in dermis
  • provides strength
• elastin:

  • elastic recoil of skin
  • does not regenerate (scar tissue)
• papillary dermis:

  • just below BMZ
  • has dermal papillae that join with rete ridges
  • capillaries provide oxygen + nutrients to epidermis
  • blisters occur at junction of papillary dermis + epidermis
  • has pain receptors
  • contains collagen
• reticular dermis:

  • base of dermis that makes up 80% of thickness
  • contains dense collagen + cutaneous blood vessels
• cellular contacts:

  • desmosomes: attach cells to each other
  • hemidesmosomes: attach cells to basement membrane

  
• dermal key cells:

  • fibroblasts: produce collagen + elastin
  • mast cells: histamines
  • macrophages: derived from monocytes
  • lymphoctes: immune response
• dermal functions:

  • nutritional support of epidermis through vascularization
  • help restore skin integrity after damage to epidermis
  • cells fight infection by phagocytosis
  • vessels help with thermoregulation
  • neural supply for sensation
• subcutaneous tissue:

  • hypodermis
  • fascia, connective tissue, + fat cells that attach skin to underlying structures
  • large blood supply
  • insulates + protects underlying structures
  • contains vitamins A, D, E + K stored in adipose tissue
  • contains deep lymphatic vessels
• skin changes with age include decreased:

  • dermal thickness
  • recoil of elastin fibers
  • height of rete ridges
  • activity of sweat glands
  • metabolic rate
  • circulation
  • epidermal regeneration