Integumentary system

• FUNCTIONS of the INTEGUMENTARY SYSTEM:

  • Mechanical Damage (bumps) - Physical barrier contains keratin, which toughens cells; fat cells to cushion blows; and both pressure and pain receptors, which alert the nervous system to possible damage.
• FUNCTIONS of the INTEGUMENTARY SYSTEM: Protects deeper tissues from:

  • Chemical damage (acid bases) - Physical barrier contains keratin, which toughens cells; fat cells to cushion blows; and both pressure and pain receptors, which alert the nervous system to possible damage.
• FUNCTIONS of the INTEGUMENTARY SYSTEM: Protects deeper tissues from:

  • Microbe damage - Has an unbroken surface and "acid mantle" (skin secretions are acidic and thus inhibit microbes, such as bacteria). Phagocytes ingest foreign substances and pathogens, preventing them from penetrating into deeper body tissues.
• FUNCTIONS of the INTEGUMENTARY SYSTEM: Protects deeper tissues from:

  • Ultraviolet (UV) radiation - Melanin produced by melanocytes offers protection from UV damage
• FUNCTIONS of the INTEGUMENTARY SYSTEM: Protects deeper tissues from:

  • Thermal (heat or cold) damage - contains heat/cold/pain receptors
• FUNCTIONS of the INTEGUMENTARY SYSTEM: Protects deeper tissues from:

  • Desiccation (drying out) - contains a water-resistant glycolipid from keratin
• FUNCTIONS of the INTEGUMENTARY SYSTEM:

  aids in body heat loss or heat retention

  • heat loss: by activating sweat glands and allowing blood to flush into skin capillary beds so that heat can radiate from the skin surface
  • Heat retention: by not allowing blood to flush into skin capillary beds
• FUNCTIONS of the INTEGUMENTARY SYSTEM:

  Aids in excretion of urea and uric acid - contained in perspiration produced by sweat glands.
• FUNCTIONS of the INTEGUMENTARY SYSTEM:

  synthesizes in vitamin D: modified cholesterol molecules in skin converted to vitamin d in the presence of sunlight
• Types of Skin

  • Thick skin
  • Covers palms and soles
  • Dermal papillae are longer
  • Contains numerous sweat glands
• Types of Skin

  • Thin skin
  • Covers the whole body except palms and soles
  • Stratum basale similar to thick skin but thinner corneum layer and s. spinosum
  • Stratum granulosum and lucidum are not present
• Layers of the skin

  • Epidermis - consists mainly of stratified squamous keratinized epithelium
  • Dermis - A connective tissue that supports the epidermis and it binds it to the subcutaneous tissue
  • Hypodermis - A loose connective tissue that attaches the skin to the underlying tissue
• Epidermis - consists mainly of stratified squamous keratinized epithelium.

  forms the major distinction between thick and thin skin

  • keratinocytes - Composed of Cells (parenchyma)
  • composed of stratified squamous epithelium that is capable of keratinizing or becoming hard and tough.
• 3 epidermal cell types present:

  • Melanocytes - pigment producing; found in the basal layer
  • Langherhans cells - antigen presenting cells found in the stratum spinosum layer
  • Merkel cells - tactile epithelial cells mostly found in thick skin located in the granular basal epidermal cells
• Keratinocytes

  • produce keratin – waterproofing protein
  • Originate in deeper layers & get pushed to surface – becomes keratin filled & dies
  • Connected to each other by desmosomes & tight junctions
  • Cell production & keratinization are accelerated in areas of friction
  • Callus – thickened skin
• Melanocytes

  • Produce melanin which accumulates on superficial side of nucleus
  • Prevents DNA mutation from the UV radiation
  • UV increases melanin production
  • Same number in everyone, but different amount of pigment produced
• Melanocytes

  • Melanosomes- membrane bound granules where melanin is produced
  • Accumulation of melanin results in freckles and moles
  • Comprise 7-10% of the cells present in the skin
  • Bound to basal lamina by hemidesmosome
• Epidermis – Skin Color

  Types of pigment present

  • Melanin – brown, black pigment
  • Carotene
  • Orange-yellow pigment from some vegetables
  • Vitamin A precursor – vitamin A forms retinal which is needed for sight
  • Accumulates in adipose and stratum corneum cells
  • Hemoglobin
  • Red, oxygen-carrying pigment in erythrocytes
  • More obviously detected in fair skin
• Langerhans Cells

  • Antigen-presenting cells
  • Present also in other stratified squamous epithelia ( oral cavity, esophagus and vagina)
  • Comprise 3-8% of the cell population present in the epidermis
  • Contain Birbeck or vermiform granules
• Merkel Cells

  • Most numerous in palms and soles
  • Bound to keratinocytes by desmosomes
  • Disc-shaped cells with short cytoplasmic processes
  • Merkel disc- Merkel cell + axon termination
  • sensory receptor that responds to pressure or touch
• SKIN: EPIDERMIS - The epidermis is composed of up to five(5) layers or strata:

  • Stratum Basale
  • Spinosum
  • granulosum
  • lucidum - found only in thick skin
  • corneum
• Like all other epithelial tissues, the epidermis is avascular - it has no blood supply of its own.
• 5 strata of the Epidermis From DEEP to SUPERFICIAL

  Stratum basale (germinativum) -

  • highly mitotic (produces new skin layer)
  • ~ 25% melanocytes
  • deepest layer of the epidermis (closest to the dermis).
  • found close to the dermal blood supply
• 5 strata of the Epidermis From DEEP to SUPERFICIAL

  Stratum basale (germinativum) -

  • consists of a single layer of columnar or cuboidal cells
  • which rest on the basement membrane.
  • Basal cells are stem cells of the epidermis
  • Their mitotic activity replenishes the cells in more superficial layers as these are eventually shed from the epidermis
• 5 strata of the Epidermis From: DEEP to SUPERFICIAL

  Stratum spinosum -

  • Slightly mitotic
  • Contains Langerhan’s macrophages
  • Several layers of many sided cells (looks spiny)
• 5 strata of the Epidermis From: DEEP to SUPERFICIAL

  Stratum granulosum -

  • Also contains Langerhans cell
  • Made up of 3-5 layers of flattened keratinocytes
  • contains keratohyaline granules (helps form keratin)
  • Contains lamellar granules
• 5 strata of the Epidermis From: DEEP to SUPERFICIAL

  Stratum lucidum -

  • ONLY found in thicker epidermis – palms, soles, callus
  • Completely keratinized (and dead!)
  • contains 4-6 layers of closely packed, clear cells that contain gel-like substance eleiden
• 5 strata of the Epidermis From: DEEP to SUPERFICIAL

  Stratum corneum -

  • Outermost layer
  • Also completely keratinized
  • 15-20 rows of flat Dead cells
  • Tough, waterproofing protection
• Individual cells are difficult to observe because

  (1) nuclei can no longer be identified,

  (2) the cells are very flat and

  (3) the space between the cells has been filled with lipids, which cement the cells together into a continuous membrane.
• SKIN: Epidermis

  • Stratum basale/germinativum.
  • The deepest cell layer of the epidermis
  • lies closest to the dermis and is connected to it along a wavy a borderline that resembles corrugated cardboard
• SKIN: Epidermis

  • Stratum spinosum - As the epidermal cells move away from the dermis and become part of the more superficial layers
• SKIN: Epidermis

  • Stratum granulosum - Upon reaching the stratum granulosum, the layers become flatter and increasingly full of keratin.
• SKIN: Epidermis

  • Stratum lucidum - Finally, they die, forming the clear stratum lucidum; this latter epidermal layer is not present in all skin regions
• SKIN: Epidermis

  • Stratum corneum. The outermost layer, the stratum corneum, is 15 to 20 cells layers thick.
  • Cornified cells. The shingle like dead cell remnants, completely filled with keratin, are referred to as cornified or horny cells.
• SKIN: Dermis - The underlying dermis is mostly made up of dense connective tissue.

  • Major regions. The dense (fibrous) connective tissue making up the dermis consists of two major regions -
  • papillary region
  • reticular region
• Dermis/Corium

  • Deeper layer of skin
  • Contains hair follicles, glands, nerves, vessels
  • All four tissue types present
  • Mainly strong, flexible CT - Two layers
• Dermis: Papillary layer

  • Contains Areolar CT
  • Dermal papillae
  • Meissner’s Corpuscles – nerve (touch) receptors
  • Indent into epidermis
  • forms fingerprints
  • Important for grip
  • Contains blood vessels
• Dermis: Reticular layer

  • Dense irregular CT
  • contains blood vessels, nerves, glands, adipose
  • Collagen – prevents overstretching and tearing of skin
  • Elastin – allows skin to stretch
  • stretch marks – dermal tears
• SKIN: DERMIS

  • Collagen - are responsible for the toughness of the dermis
  • Elastic fibers - give the skin its elasticity
  • Blood vessels - The dermis is abundantly supplied with blood vessels that play a role in maintaining body temperature homeostasis
  • Nerve supply - The dermis also has a rich nerve supply; many of the nerve endings have specialized receptor end-organs
• SKIN: DERMIS

  • Constitute the major part of the dermal papillae
  • composed of loose CT, with fibroblast and other CT cells
  • Mast cells and macrophage
  • Composed of irregular dense connective tissue and has more fibers than cells
  • elastic fibers is present providing elasticity to the skin