Integumentary System

• Layers of the skin

  • Epidermis
  • Dermis
  • Hypodermis
• Epidermis


  • Composed of stratified squamous cells
  • Superficial most layer
• Dermis


  • Deep to the epidermis
  • Mostly dense irregular connective tissue: areolar connective tissue found in the papillae
  • Houses most structures of skin
• Hypodermis


  • Deep to the dermis
  • Made up of adipose tissue
  • Helps insulate and store energy
• Epidermis


  Composed keratinized stratified squamous epithelium
• Keratin


  • A fibrous protein that provides strength and rigidity
  • Also resistant to acids and bases to prevent infection
• Layers of the epidermis

  • Stratum basale
  • Stratum spinosum
  • Stratum ganulosum
  • Stratum lucidum
  • Stratum corneum
• Stratum basale


  • Deepest layer
  • A single row of stem cells
  • Actively mitotic
  • Produces two daughter cells
• Stratum spinosum


  • Several layers thick
  • Cells joined together by desmosomes
  • Produce pre-keratin filaments (a keratin precursor)
  • Abundant with dendritic cells
• Stratum granulosum


  • Thin stratum
  • Dendritic cells found here
  • Cells become flat
  • Keratinization begins
• Stratum Lucidum


  • Only found in thick skin (palms and feet)
  • Adds extra protection
  • Thin translucent band superficial to the stratum granulosum
• Stratum Corneum


  • 20-30 rows of dead, flat, anucleated, keratinized cells
  • Can make up three quarters of the epidermis thickness
  • Protect deeper cells from water loss
  • Protect from abrasion
  • Barrier against biological, chemical and physical assault
• Dermis


  • A layer composed of strong, flexible connective tissue
  • Houses hair follicles, oil glands and sweat glands
  • Provides a matrix for nerves, blood vessels and lymphatic vessels to run through
• Layers of the Dermis

  • Papillary layer
  • Reticular layer
• Papillary Layer


  • Areolar connective tissue with collagen and elastic fibers
  • Vascularized
  • Relatively loose tissue
  • Contains dermal papillae
• Reticular Layer


  • Makes up 80% of dermal thickness
  • Mostly made up of dense irregular connective tissue
  • Contains elastic fibers to provide stretch and recoil
  • Contains collagen fibers
• Factors contributing to normal skin color

  • Melanin
  • Carotene
  • Hemoglobin
• Melanin


  • Pigment made by the skin
  • Important in protecting the skin against UV rays
  • Created by melanocytes and packaged in melanosomes
• Carotene


  • Important for vitamin A production
  • Yellow/orange
  • Accumulates in corneum and hypodermis
• Hemoglobin


  • Due to blood vessels of the skin
  • Pinkish in hue due to oxygenated blood
• Clinical skin conditions

  • Cyanosis
  • Erythema
  • Pallor
  • Jaundice
  • Bruising
• Cyanosis


  Blue skin due to low oxygenation of hemoglobin
• Erythema


  Reddish skin due to increased blood flow to the skin surface
• Pallor


  Pale in color
• Jaundice


  Skin yellow in color
• Bruising


  Clotted blood beneath the skin
• Hair


  • Referred to as pilus
  • Made up of keratinized cells
• Three kinds of hair

  • Lanugo – fetal hair; almost completely gone at birth
  • Vellus – Short fine hair found all over the body; more prominent on the arms and legs
  • Terminal hair – Hair of the scalp, eyebrows, facial hair and armpits
• Major parts of hair

  • Hair bulb – composed of living epithelial cells being added to hair
  • Root – section of hair going from bulb to surface; made of dead epithelial cells
  • Shaft – the section that extends off of the skin; composed of dead epithelial cells
• Sudoriferous Glands


  • Found in all skin except certain parts of genitalia
  • ~ 3 million per person
  • Controlled by nervous system
  • Contain myoepithelial cells
• Myoepithelial cells


  • Epithelial cells that possess actin and myosin
  • Contract upon nervous system stimulation to force sweat into ducts
• Two main types of sudoriferous glands

  • Eccrine (merocrine) sweat gland
  • Apocrine sweat gland
• Eccrine (merocrine) sweat gland


  • Most numerous
  • A merocrine gland: if the secretions of that cell are excreted via exocytosis from secretory cells into an epithelial-walled duct or ducts and then onto a bodily surface or into the lumen
  • Lumen typically smaller than apocrine
  • Abundant on palms, soles, and forehead
  • Function throughout life
  • Ducts secrete sweat through pores of the skin
  • Function in thermoregulation
  • Regulated by the sympathetic nervous system
  • Secrete sweat (99% water, salts, Vitamin C, antibodies, Dermcidin, metabolic wastes)
• Apocrine sweat gland


  • Mostly confined to axillary and genital areas, except for modified forms
  • Secretes a sweat-fat-protein liquid (viscous, milk or yellowish, eaten by commensal bacteria which creates an odor)
  • Lumen larger than eccrine
  • Ducts empty into hair follicles
  • Start functioning after puberty
  • Function not completely understood; may act as a sexual scent gland
• Modified apocrine glands


  • Ceruminous glands – secrete earwax in ear
  • Mammary glands – secrete milk
• Sebaceous (oil) gland


  • Found in all parts of skin except the palms of hands and soles of feet
  • Mostly secrete oil into hair follicles
  • Relatively inactive until puberty (stimulated by hormones)
  • Secretes sebum (oily holocrine secretion, acts as a bactericide, softens skin and hair)
• Functions of the Integumentary System

  • Protection (chemical, physical, biological barriers)
  • Body temperature regulation
  • Cutaneous sensations
  • Metabolic function
  • Blood reservoir
  • Excretion
• Metabolic function

  1. Occurs in the keratinocytes of the epidermis

  2. Using energy from UV-B light, it converts cholesterol into Vitamin D3

  3. Vitamin D3 is secreted into the blood stream and carried to the liver and converted to calcidiol

  4. Then carried to the kidneys where it is converted to calcitriol (active Vitamin D)

  5. Vitamin D (calcitriol) – a hormone that stimulates the absorption of calcium and phosphate in the GI tract
• If the body is hot

  Blood capillaries will vasodilate, bringing more blood to the surface. The heat of the blood passed to the media of the external environment
• If body is cold

  Blood capillaries will vasoconstrict, bringing less blood to the surface and keeping the blood near the core of the body