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• Integumentary system


  • Helps maintain a constant body temperature
  • Protects the body
  • Provides sensory information about the surrounding environment
• The skin is the most easily inspected and exposed organ of the body

  
• The skin's protective features ward off damage from trauma, sunlight, microbes, and pollutants in the environment
• Skin reflects our emotions and some aspects of normal physiology

  
• Changes in skin color may indicate homeostatic imbalances in the body
• Abnormal skin eruptions or rashes may reveal systemic infections or diseases of internal organs

  
• Conditions like warts, age spots, or pimples may involve the skin alone
• The skin is important to self-image and many people spend time and money to restore it to a more normal or youthful appearance
• Integumentary system


  Composed of the skin, hair, oil and sweat glands, nails, and sensory receptors
• Dermatology


  The medical specialty that deals with the structure, function, and disorders of the integumentary system
• Skin


  Also known as the cutaneous membrane, covers the external surface of the body and is the largest organ of the body in weight

  
• The skin ranges in thickness from 0.5 mm on the eyelids to 4.0 mm on the heels, and is 1-2 mm thick over most of the body

  
• Epidermis


  The superficial, thinner portion of the skin, composed of epithelial tissue

  
• Dermis


  The deeper, thicker connective tissue portion of the skin

  
• Subcutaneous (subQ) layer


  Also called the hypodermis, consists of areolar and adipose tissues and attaches the skin to underlying fascia

  
• Functions of the Integumentary System

  • Regulates body temperature
  • Stores blood
  • Protects body from external environment
  • Detects cutaneous sensations
  • Excretes and absorbs substances
  • Synthesizes vitamin D
• Epidermis


  • Composed of keratinized stratified squamous epithelium
  • Contains four principal cell types: keratinocytes, melanocytes, intraepidermal macrophages, and tactile epithelial cells
• Keratinocytes


  The most abundant epidermal cells, produce the protein keratin
• Melanocytes


  Produce the pigment melanin, which contributes to skin color and absorbs ultraviolet light
• Intraepidermal macrophages (Langerhans cells)

  Participate in immune responses against microbes that invade the skin
• Tactile epithelial cells (Merkel cells)


  Detect touch sensations
• Layers of the epidermis

  • Stratum basale
  • Stratum spinosum
  • Stratum granulosum
  • Stratum lucidum (in thick skin)
  • Stratum corneum
• Stratum basale


  The deepest layer of the epidermis, contains stem cells that continually produce new keratinocytes
• Stratum spinosum


  Contains keratinocytes with keratin intermediate filaments that insert into desmosomes, providing strength and flexibility
• Stratum granulosum


  Contains keratinocytes undergoing apoptosis, with keratohyalin granules that assemble keratin, and lamellar granules that release a lipid-rich sealant
• Stratum lucidum


  Present only in thick skin, contains flattened clear dead keratinocytes with large amounts of keratin and thickened plasma membranes
• Stratum corneum


  The outermost layer of the epidermis, contains 25-30 layers of extremely thin, flat, dead keratinocytes filled with keratin
• Stratum Corneum


  • Consists of 25 to 30 layers of flattened dead keratinocytes
  • Cells are extremely thin, flat, plasma membrane-enclosed packages of keratin that no longer contain a nucleus or any internal organelles
  • Cells within each layer overlap one another like the scales on the skin of a snake
  • Neighboring layers of cells form strong connections with one another
  • Plasma membranes of adjacent cells are arranged in complex, wavy folds that fit together like pieces of a jigsaw puzzle to hold the layers together
  • Cells are continuously shed and replaced by cells from the deeper strata
  • Multiple layers of dead cells help protect deeper layers from injury and microbial invasion
  • Constant exposure of skin to friction stimulates increased cell production and keratin production that results in the formation of a callus
• Stratum Spinosum


  • Consists of numerous keratinocytes arranged in 8-10 layers
  • Cells in the more superficial layers become somewhat flattened
  • Keratinocytes produce coarser bundles of keratin in intermediate filaments than those of the basal layer
  • Cells appear to be covered with thornlike spines where the membranes join at desmosomes
• Keratinization


  The process by which cells accumulate more and more keratin as they move from one epidermal layer to the next
• Growth of the Epidermis

  1. Cells form in the stratum basale

  2. Cells rise to the surface

  3. Cells become keratinized

  4. Keratinized cells slough off and are replaced by underlying cells
• The whole process by which cells form in the stratum basale, rise to the surface, become keratinized, and slough off takes about four to six weeks in an average epidermis of 0.1 mm thickness
• Nutrients and oxygen diffuse to the avascular epidermis from blood vessels in the dermis
• The epidermal cells of the stratum basale are closest to these blood vessels and receive most of the nutrients and oxygen
• The rate of cell division in the stratum basale increases when the outer layers of the epidermis are stripped away, as occurs in abrasions and burns
• Hormonelike proteins such as epidermal growth factor (EGF) play a role in regulating the remarkable growth of the epidermis
• An excessive amount of keratinized cells shed from the skin of the scalp is called dandruff
• Papillary Region of the Dermis

  • Contains thin collagen and fine elastic fibers
  • Surface area is greatly increased by dermal papillae, small nipple-shaped structures that project into the undersurface of the epidermis
  • All dermal papillae contain capillary loops
  • Some dermal papillae contain tactile receptors called corpuscles of touch or Meissner corpuscles
  • Some dermal papillae contain free nerve endings that initiate signals for sensations of warmth, coolness, pain, tickling, and itching

  
• Reticular Region of the Dermis

  • Contains bundles of thick collagen fibers, scattered fibroblasts, and various wandering cells
  • Some adipose cells can be present in the deepest part of the layer, along with some coarse elastic fibers
  • Collagen fibers are arranged in a netlike manner and have a more regular arrangement than those in the papillary region
  • The more regular orientation of the large collagen fibers helps the skin resist stretching
  • Blood vessels, nerves, hair follicles, sebaceous glands, and sudoriferous glands occupy the spaces between fibers

  
• Melanin


  A pigment that imparts a wide variety of colors to skin, ranging from pale yellow to reddish-brown to black