GENBIO - Integumentary System

• The 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
• Layers of the skin

  • Epidermis
  • Dermis
  • Hypodermis (Subcutaneous tissue)

  
• 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
  • The keratinocytes of the epidermis are constantly lost at its surface but are also constantly replaced by other cells moving from deeper layers
  • New keratinocytes are produced when keratinocyte stem cells in stratum basale undergo mitosis
  • As new cells form, they push older cells to the surface, where they slough off
  • As they move from the deeper epidermal layers to the surface, the keratinocytes change shape and chemical composition, through the process called keratinization where the cells accumulate keratin
  • 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 the 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
  • Melanoblast converts tyrosine into DOPA (dihydroxyphenylalanin) by oxidation with the presence of enzyme tyrosinase. DOPA is further converted to DOPA-Quinone - a series of reaction result to production of melanoprotein (melanin) giving a brown color to the skin
  • The size and distribution of melanosomes determine skin color. Melanin production is determined genetically but can be influenced by ultraviolet light (tanning) and hormones
• 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
  • Cells of the dermis: Fibroblast, Macrophages, Mast cells, Lymphocytes

  
• Layers of the dermis

  • Papillary Layer
  • Reticular Layer

  
• 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
  • Brings blood vessels close to the epidermis

  
• 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
  • Glands
  • Nails

  
• Hair


  • The hair on the head acts as a heat insulator and protects against ultraviolet light and abrasion
  • The eyebrows keep sweat out of the eyes, the 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. The root and shaft of a hair are composed of dead keratinized epithelial cells. The hair bulb produces the hair in cycles, with a growth stage and a resting stage
  • 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"
• Skin glands


  • Sebaceous glands
  • Sweat glands
  • Ceruminous glands
  • Mammary glands
• Sebaceous glands


  Secretes 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
  • Sweat can be activated by emotional stress—used in polygraph lie detector tests
  • 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