Integumentary System Three Layers

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Integumentary SystemThree Layers

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Epidermis

• Stratum basale - single layer of columnar cells
  that undergo mitosis
• Stratum spinosum - 8-10 rows of cells

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• Stratum granulosum - 3-5 layers of flat cells
  containing keratohyaline and showing
  characteristics of cell death
• Stratum lucidum - a clear layer found only in
  thick skin on the palms and soles

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• Stratum corneum - 20-30 layers of flat dead cells
  containing keratin which waterproofs and toughens
  the skin

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• Appearance of the skin - important clinically -
• Pale skin - ?
• Red flushed skin - ?
• Rashes - ?

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• Besides preventing the entry of substances from
  the outside, the epidermis also prevents the loss
  of body constituents
• It can absorb any substance that can dissolve
  keratin and is lipid soluble i.e., salves to
  relieve aches and pains, cortisol creams, some
  toxins and pesticides

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• Dermis - made of dense irregular CT, blood and
  lymph vessels, glands and sensory receptors (is
  the leather of an animal skin)
• Papillary layer - upper fifth dermal
  papillae are reflected on the surface as friction
  ridges called fingerprints on the fingers
  contain Meissners corpuscles for touch

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• Reticular layer - lower four fifths contain
  arteriovenous (AV) anastomoses that allow blood
  to bypass capillaries and conserve heat also
  contain sweat and sebaceous glands and Pacinian
  corpuscles
• Subcutaneous layer - contains areolar C.T. and
  adipose tissue responsible for female body
  contours aka - superficial fascia or hypodermis
  attaches dermis to underlying organs -bones and
  muscles

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Epidermal Cells

• Keratinocyte - the predominant cell in the
  stratum basale, produces keratin
• Melanocyte - produces melanin, makes up 1/4 of
  the stratum basale

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• Langerhans cell - immune function
• Merkel cells - combines with disclike sensory
  nerve endings to make Merkels discs

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Just what does the skin do?
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Functions of the Skin

• Protection - physical (cells close), chemical
  (melanin) and biological (Langerhans cells)
  barrier
• Temperature regulation - sweating, arteriovenous
  anastomoses
• Absorption

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• Excretion - water, salt, urea
• Receive stimuli - touch, heat. etc.
• Start the production of vitamin D
• Immunity - lysozyme in sweat, Langerhans cells

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Skin Color

• Melanin - melanocytes have dendrite-like
  extensions that transfer pigments outward and
  then the keratinocytes take up the melanin by
  phagocytosis. UV radiation increases production
• Variations
• Albinism - inability to produce
  melanin in skin, eyes and hair

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• Freckles - patches of melanin
• Vitiligo - partial or complete loss of
  melanin in an area

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• Carotene - yellow orange pigment in dermis and
  epidermis
• Hemoglobin - in dermal capillaries reflect
  pinkish color in fair skin

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Accessory Skin Organs

• Hair - has a protective function
• 1. Shaft (superficial part) and root (below
  surface)

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• a. Inner medulla - contain air spaces
• b. Middle cortex - contains pigment, and air
  spaces in white hair. Graying is due to the
  inability to make melanin.

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• c. Outer cuticle - keratinized thin layer whose
  cells overlap like roof tiles it keeps hair from
  matting

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• 2. Hair follicle - surrounds the root
• a. External root sheath a continuation
  of the stratum spinosum and basale
• b. Internal root sheath - formed by
  the matrix

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• c. Bulb - base of the follicle
• d. Papilla - indentation in the bulb containing
  loose CT and blood vessels
• e. Matrix - germinal layer in bulb produces new
  hair derived from the stratum basale (Makes
  sense, doesnt it?)

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• Hair loss - normal in the scalp - 70-100 hairs
  per day. Hair goes thru growth and rest periods.
• 3. Arrector pili - muscle which when it
  contracts causes goose bumps

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• 4. Root hair plexus - around bulb is
  sensitive to touch
• 5. Color is mainly due to melanin blond
  and red hair contains iron and sulfur

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Nails

• 1. Free edge - projects beyond the distal end of
  the digit
• 2. Nail body - visible part
• 3. Nail root - hidden part

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• 4. Nail bed - epidermis beneath the nail. The
  proximal part of this bed is the nail matrix
  where new nail is produced. The lunula is part
  of the matrix that can be seen thru the nail
  body.

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Glands of the Skin

• Sweat (sudoriferous)
• Apocrine - begin to function at puberty
  contain organic substances which produce an odor
  when broken down open into hair follicles

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• Eccrine - numerous in palms and soles contains
  mainly salty water opens via a pore onto the
  surface
• Functions in maintaining body temperature,
  eliminating wastes, and immunity

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Oil (sebaceous)

• a. Secretes sebum containing fat, salt,
  cholesterol and protein
• b. Most are connected to hair follicles, some
  open directly onto the surface - lips, glans penis

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• c. Function - keeps hair from drying, forms
  a protective film to prevent excess water
  evaporation, inhibits bacterial growth
• Ceruminous (wax) - in external auditory meatus
  secretes cerumen (wax) which prevents the
  entrance of foreign bodies