Integumentary

• Integumentary system


  Consists of the skin and accessory structures, such as hair, glands, and nails
• Integumentary system


  • Forms the boundary between the body and the external environment, thereby separating us from the external environment while allowing us to interact with it
• Major functions of the integumentary system

  • Protection
  • Excretion
  • Sensation
  • Temperature regulation
  • Vitamin D production
• Protection


  • Protects underlying structures from mechanical damage or abrasion
  • Reduces the negative and harmful effects of ultraviolet light
  • Keeps microorganisms and toxic substances from entering the body
  • Reduces water loss from the body, preventing dehydration
• Excretion


  Small amounts of waste products, such as urea, uric acid, and ammonia, are excreted through the skin and glands
• Sensation


  Acts as sense organ; has sensory receptors that can detect heat, cold, touch, pressure, and pain
• Temperature regulation


  • The modulation in the amount of blood flow through the skin and the activity of sweat glands contribute to temperature regulation
  • Blood vessels dilate when it is hot and constrict when it is cold
  • Sweat glands produce sweat when it is hot and stop sweat production when it is cold
• Vitamin D production


  When exposed to ultraviolet light, the skin produces a molecule (7 dehydrocholesterol) that can be transformed into vitamin D, an important regulator of calcium homeostasis
• Epidermis


  • The uppermost layer of the skin; approximately 0.04 to 1.5 mm thick
  • Made of stratified squamous epithelium divided into five strata
  • No blood vessels: receive nutrients and excrete waste products by diffusion
  • Composed of several types of cells (keratinocytes, melanocytes, Langerhans cell and Merkel cells)
• Keratinocytes


  Predominant cells in the epidermis; contain keratin filaments in their cytoplasm
• Keratinization


  1. As new cells form, they push older cells to the surface, where they slough off

  2. During keratinization, the cells eventually die and produce an outer layer of dead, hard cells that resists abrasion and forms a permeability barrier
• Layers of epidermis


  • Stratum Germinativum (Basale)
  • Stratum Spinosum
  • Stratum Granulosum
  • Stratum Lucidum
  • Stratum Corneum
• Stratum Germinativum (Basale)


  • Deepest stratum of the epidermis; single layer of cuboidal or columnar cells
  • Produces cells of the most superficial strata; melanocytes produce and contribute melanin, which protects against ultraviolet light
• Stratum Spinosum


  • Spine-like appearance cells; 8–10 layers of many-sided cells
  • Produces keratin fibers; lamellar bodies form inside keratinocytes
• Stratum Granulosum


  • Two to five layers of flattened, diamond-shaped
  • Produces keratohyalin granules; lamellar bodies release lipids from cells
  • Cells die - loss of nuclei and cellular contents except keratin filament and matrix materials
• Stratum Lucidum


  • Three to five layers of dead cells; appears transparent
  • Present in thick skin (skin on palms and soles), absent in most thin skin
• Stratum Corneum


  • Most superficial stratum of the epidermis; 25 or more layers of dead squamous cells
  • Loss of cell nuclei and all cellular contents except keratin filaments and matrix materials of granular cell
  • Provides structural strength due to keratin within cells; prevents water loss due to lipids surrounding cells; sloughing off of most superficial cells resists abrasion
• Melanin


  • Skin color is primarily due to the pigment called melanin
  • Melanin absorbs harmful UV radiation
  • Melanin is produced in melanocytes; melanin is packaged in melanosomes
  • Melanosomes enter skin cells and release melanin
• Melanin production


  1. Melanoblast converts tyrosine into DOPA (dihydroxyphenylalanin) by oxidation with the presence of enzyme tyrosinase

  2. DOPA is further converted to DOPA-Quinone - a series of reaction result to production of melanoprotein (melanin) giving a brown color to the skin
• Dermis


  • Deep part of skin; connective tissue composed of two layers - papillary layer and reticular layer
  • Composed mainly of dense collagenous fibers—responsible for its elasticity and durability
  • With blood vessels; contains fats, nerves, smooth muscles, hair follicles, and glands
• Papillary layer


  • Loose connective tissue; brings blood vessels close to the epidermis
  • Contains dermal papillae - projections that extend to the epidermis and form curving ridges into fingerprints and footprints; increase friction and improve grip
• Reticular layer


  • Mat of collagen and elastic fibers; dense irregular connective tissue
  • Main fibrous layer of the dermis; strong in many directions; forms cleavage lines
  • Contains glands and hair follicle
• Hypodermis / Subcutaneous layer


  • Not part of the skin; loose connective tissue with abundant deposits of adipose tissue
  • Attaches skin to the underlying structure (bones and muscles)
  • Adipose tissue provides energy storage, insulation, and padding; blood vessels and nerves from the subcutaneous tissue supply the dermis
• Accessory skin structures


  • Hair
  • Sebaceous gland
  • Sweat gland
  • Nails
• Hair


  • The hair on the head acts as a heat insulator and protects against ultraviolet light and abrasion
  • Eyebrows keep sweat out of the eyes, eyelashes protect the eyes from foreign objects, and hair in the nose and ears prevents dust and other materials from entering
  • Axillary and pubic hair are a sign of sexual maturity and protect against abrasion
  • A hair has three parts: shaft, root, and hair bulb
  • Hair color is determined by the amount and kind of melanin present
  • Contraction of the arrector pili muscles, which are smooth muscles, causes hair to "stand on end" and produces "goose bumps"
• Sebaceous glands


  Secrete an oily substance called sebum that is made of fat (lipids) and the debris of dead fat-producing cells, for lubricating hair and prevents skin drying
• Sweat glands


  • Eccrine sweat gland – present everywhere but numerous in palms and soles; secretes mostly water and salts; for temperature regulation
  • Apocrine sweat gland – located in armpits and genitalia; secretes organic substances that are broken down by bacteria to produce body odor; signal sexual maturity
• Nails


  • A thin plate of dead, keratinized stratum corneum cells
  • They grow continuously and serves as a protective plate and enhances sensation of the fingertip
  • The nail root is covered by skin, and the nail body is the visible part of the nail
• Partial-thickness burns damage only the epidermis (first-degree burn) or the epidermis and the dermis (second-degree burn)
• Full-thickness burns (third-degree burns) destroy the epidermis, the dermis, and usually underlying tissues
• As the body ages, blood flow to the skin declines, the skin becomes thinner, and elasticity is lost
• Sebaceous and sweat glands become less active, and the number of melanocytes decreases