Integumentary System

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Integumentary System

• Skin

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Integument

• Important organ represents 15 of total body
  weight.
• Functions
• a) protection (mechanical barrier)
• b) detective organ (receptors)
• c) antiseptic barrier (chemical barrier)
• d) thermoregulation
• e) secretion and absorption
• f) Vitamin D synthesis

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Integument

• Two Layers
• a) epidermis (ectodermal)
• b) dermis (mesodermal)
• Hypodermis - below dermis, attaches skin to body
  not part of the skin.

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Integument

• Boundary between epidermis and dermis marked by
  prominent papillations dermal papilla.
• These folds manifest themselves on the surface of
  the skin, especially in thick skin finger
  prints, etc. Palmar and Plantar surfaces

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Integument

• Epidermis most cells from superficial ectoderm
  (keratinocytes).
• Pigment cells in basal layer from neural ectoderm
  (melanocytes). Pigment cells form melanin.
• Skin color due to
• a) carotene - yellow pigment in all cells
• b) blood vessels in underlying dermis
• c) melanin pigment in melanocytes at basal
  layer of epidermis.

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Integument

• Epidermal cells undergo keratinization as they
  move from the basal surface to the free surface
  keratin or its intermediate protein replaces cell
  cytoplasm causing cell death.
• Cells become progressively flattened as they move
  to the surface.
• Langerhans Cell antigen presenting cell of
  epidermis, mainly in stratum spinosum.
• Merkel's Cell - disc - tactile receptor in
  epidermis.

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Thin Skin
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Epidermis

• Epidermis composed of five layers
• a) stratum corneum
• b) stratum lucidum
• c) stratum granulosum
• d) stratum spinosum
• e) stratum germinativum (basale)

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Epidermis

• Stratum Corneum - outermost layer of skin clear,
  dead, flat, scale-like cells fused together.
  Cytoplasm completely replaced by keratin. Cells
  constantly sloughed off.
• Stratum Lucidum - thin, clear, translucent layer.
  Cells flat and closely packed. Cytoplasm
  contains keratohyalin, a precursor product of
  keratin. Also contains eleiden, a refractile
  substance related to keratohyalin. Produces the
  clear nature of these cells.

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Skin Sensorial Receptors
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Epidermis

• Stratum Granulosum - thin, darkly pigmented layer
  of cells, 3-5 cell layers thick. Nuclei present
  in these cells tonofilaments present and
  keratohyalin (granules). Cells flatten and die
  in this layer.
• Stratum Spinosum - cells polyhedral (cuboidal)
  with spaces between each. Surfaces of cells with
  desmosomes. Many tonofibrils. Keratinization
  begins here. Sometimes included with str. germ.
  as Stratum Malpighii.

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Stratum Spinosum
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Epidermis

• Stratum Germinativum (basale) - single layer of
  cuboidal cells have attachment process on basal
  surface attaching epidermis (hemidesmosome) to
  basement membrane (outer dermis).
• Cells divide and move toward the surface. -
  melanocytes (derived from neural crest) are below
  and send cytoplasmic processes up between
  germinativum cells.

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Dermis

• Papillary Dermis - outer layer, reticular fibers
  on outer surface contribute to lamina anchoring
  the epidermis. Small fibers and more cells
  (fibroblasts and macrophages) present. Some fat
  may be present, pigment cells may occur in areola
  and anal ring.
• Reticular Dermis - inner layer strongly fibroid
  relatively acellular. Fibers long and orient in
  layers Langer's Lines. Thickest layer hair
  follicles, smooth muscle and some fat present.

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Integument

• Skin Products
• 1) Nails - formed by infolding of skin layers.
  Nail bed formed by deeper layers of epidermis (s.
  spinosum and s. basale). Outer epidermal layers,
  corneum and lucidum, have high sulfur content and
  form nail proper. Pink color due to underlying
  blood vessels. Corneum forms epinychium
  (cuticle) and hyponychium

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Integument

• 2) Hair - keratinized threads composed of free
  shaft and root. Occur over entire body except
  palmar and plantar surfaces, lips, external
  genitalia and anal apertures.
• Hair root embedded in a follicle of mostly
  epidermis and dermis.

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• Hair Shaft
• a) medulla - shrunken, cornified cuboidal cells
  with air spaces between absent in blond hair
  contains pigment and soft keratin.
• b) cortex - forms bulk of hair long cornified
  cells of hard keratin. Pigment between and
  within cells.
• c) hair cuticle - outer cornified cells with no
  nucleus.

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• Hair Follicle epidermal components
• internal epithelial sheath modified corneum
• 1) follicle cuticle - cornified outer layer of
  cells facing hair shaft cuticle.
• 2) Huxley's Layer - multiple layers of
  squamoid cells with tricohyalin.
• 3) Henle's Layer - 1 cell thick, clear cells
  (squamous) with hyalin.

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• b) external epith. sheath modified str.
  spinosumDermal components dermal papilla,
  provides blood vascular supply to hair follicle.
• Sebaceous Glands and smooth muscle attach to
  hair follicle. Muscle Arrector pilae, produces
  cutis anserina (goose flesh).
• 3) Sweat Glands - located deep in the dermis
  and/or hypodermis.

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Sebaceous Gland

• Acinar gland opens to short duct into upper hair
  follicle
• Differentiate from epithelial stem cells (arrow).
• Accumulate lipid droplets
• Droplets fuse, cell bursts (holocrine)
• Sebum- TGs, waxes, cholesterol, squalene
• Begin to function at puberty

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Sweat Glands

• Simple coiled tubular gland under Autonomic
  Control
• Secretory gland in dermis, duct through epidermis
  to surface
• Stratified cuboidal epith.
• Merocrine- hypoosmotic, NaCl, urea, ammonia
• Apocrine- axial, anal, areolar larger gland
  duct opens to hair follicle.
• Odor with bacterial degrad.