Integumentary system

• Integumentary system


  Consists of skin, hair, nails and various glands
• Integumentary system


  • Two major components: Cutaneous membrane (skin) and Accessory structures (hair, nails, exocrine glands)
  • Hypodermis (subcutaneous layer) - loose connective tissue under the dermis, often not considered part of the integumentary system

  
• Structure of the integumentary system


  1. Epidermis (superficial)

  2. Dermis (underlying connective tissue)

  3. Hypodermis (subcutaneous layer)

  
• Five general functions of the integument


  • Protection
  • Temperature maintenance
  • Synthesis and storage of nutrients
  • Sensory reception
  • Excretion and secretion
• Epidermis


  Stratified squamous epithelium
• Layers of the epidermis (thick skin)

  • Stratum basale
  • Stratum spinosum
  • Stratum granulosum
  • Stratum lucidum
  • Stratum corneum

  
• Layers of the epidermis (thin skin)


  • Stratum basale
  • Stratum spinosum
  • Stratum granulosum
  • Stratum corneum

  
• Stratum basale


  Also called stratum germinativum, attached to basement membrane by hemidesmosomes, forms epidermal ridges, contains basal or germinative cells

  
• Stratum basale

  • Contours of skin follow ridge patterns, ridge contours are genetically determined and unique to each person

  
• Stratum spinosum


  Result of stem cell division
• Stratum granulosum


  Cells make a lot of keratin, a protein that provides water resistance and the foundation for hair and nails
• Stratum lucidum


  Densely packed into a highly keratinized layer, only found in thick skin

  
• Stratum corneum


  Contains 15-30 layers of keratinized or cornified dead cells, cells are connected via desmosomes and shed in large groups
• Skin color


  Role of pigmentation: Carotene is orange-yellow, Melanin is brown/yellow-brown/black and protects deeper layers from UV radiation

  
• Variations in skin color are due to differences in melanin production, not number of cells

  
• Albinism

  Light colored skin or hair due to lack of melanin production in melanocytes

  
• Dermal circulation


  Oxygenated blood is bright red, vasoconstriction causes paling, cyanosis is bluish coloration from diminished oxygen
• Vitamin D3


  Derived from a cholesterol-related steroid in the epidermis when exposed to sunlight, modified by liver and kidneys into calcitriol essential for calcium and phosphorus absorption
• Detrimental effects of sunlight


  • Skin cancers: Basal cell carcinoma, Squamous cell carcinoma, Malignant melanoma

  
• Dermal papillary layer


  Contains capillaries and nerves supplying the epidermis
• Dermal reticular layer


  • Interwoven meshwork of dense, irregular connective tissue with elastic and collagen fibers, hair follicles and sweat glands derived from epidermis extend down into this layer, cutaneous plexus of blood vessels extends up into this layer

  
• Hypodermis


  Also called subcutaneous layer, deep to the dermis, made of areolar tissue with many adipose cells, stabilizes the skin to underlying tissues

  
• Hair and hair follicles


  • Accessory organs of the integumentary system, hairs are nonliving structures produced in hair follicles, epidermal layers invaginate into the dermis to form hair follicles, hair grows according to a hair growth cycle
• Areas where hair does not project above the skin surface


  • Soles of the feet
  • Palms of the hands
  • Sides of the fingers and toes
  • The lips
  • Portions of the external genitalia
• Hair follicles


  • Epidermal layers invaginate into the dermis to form them
  • Epithelium at the base caps over the hair papilla
  • Contain connective tissue with capillaries and nerves
  • Epithelial stem cells divide to form hair matrix surrounding the papilla
• Hair growth


  1. Hair matrix grows, making hair longer

  2. Cells become keratinized and die

  3. Halfway to skin surface it becomes the hair root

  4. Above the surface it is the hair shaft

  5. Shaft has three layers: cuticle, cortex, and medulla
• Hair growth cycle


  • Will grow for 2-5 years
  • Follicle may become inactive for another 2-5 years
  • When another cycle begins, the follicle starts producing new hair and the old hair is shed
  • Variations in length come from this
  • Size of follicles and shape of hair determine straight and curly
• Hair color


  • Differences due to type and amount of melanin from melanocytes
  • Aging results in less pigment production, causing gray or white hair
• Sebaceous glands


  • Secrete oily sebum into the hair follicle
  • Secreted when arrector pili muscles contract
  • Lubricates and inhibits growth of bacteria
  • Secrete sebum directly onto skin of face, back, chest, nipples, and external genitalia
  • Sensitive to hormonal changes, accelerating at puberty
  • Inflamed glands can result in acne
• Types of sweat glands


  • Apocrine
  • Merocrine
• Apocrine sweat glands


  • Become active at puberty
  • Secrete sticky, cloudy sweat into hair follicles in armpits, around nipples, and in the pubic region
  • Sweat is food source for bacteria on skin, increasing odor
• Merocrine (eccrine) sweat glands


  • Very numerous with high numbers on soles and palms
  • Coiled tubular structure secretes watery perspiration directly onto surface of skin
  • Sweat contains electrolytes, urea, and organic nutrients
  • Function is to cool body through evaporation and provide protection
• Modified sweat glands


  • Mammary glands
  • Ceruminous glands
• Nails


  • Protect tips of fingers and toes
  • Visible nail body made of dense, keratinized cells
  • Nail bed is the deeper level of epithelium covered by nail body
  • Nail root is where the nail is produced and is covered by the cuticle
  • Lunula is the pale crescent near the root
• Skin repair


  1. Scab formation

  2. Tissue granulation

  3. Scab removal

  4. Scar formation
• Scab formation


  • A blood clot that forms on the surface
  • Is a temporary "patch" that can help prevent additional microbes from invading the injury
• Granulation tissue


  • Formed from the combination of the fibrin blood clot, fibroblasts, and capillaries
  • Macrophages clean up debris
• Scar formation


  • Formed from remaining meshwork of collagen fibers
  • Degree of scar dependent on severity and location of injury and age of patient
  • Keloid scars are thicker, raised, smooth, and shiny
• Effects of aging on the integument


  • Skin injuries and infections are more common
  • Sensitivity of immune system is reduced
  • Muscles become weaker and bone strength decreases
  • Sensitivity to sun exposure increases
  • Skin becomes dryer and flakier
  • Hair thins and loses color
  • Sagging and wrinkling of the skin occurs
  • Ability to lose heat is reduced
  • Skin repairs more slowly