Skin

• Describe the macroscopic structure of human skin?

  Epidermis, Dermis, Hypodermis
• What is the Pilosebaceous Unit?

  • Arrector Pili muscle
  • Sebaceous gland
  • Hair follicle
• What is the structure of the Hypodermis?

  • Mostly white adipose tissue with some neuromuscular bundles, lymphatics & lymph nodes
  • Some loose connective tissue - fibroblasts, macrophages & fibres
• What is the function of the Hypodermis?

  • Provide energy store - generate heat
  • Insulate underlying muscle
  • Shock absorber
  • Connects skin to underlying muscle & bone
  • Makes hormones e.g. leptin
• How does hypodermis thickness change?

  • Males - hypodermis is thickest in abdomen & shoulders
  • Females - thickest in the hips, thighs, buttocks
  • Relatively thick on palms of hands and soles of feet in both sexes
• What is the structure of the dermis?

  • Three layers:
  • Papilllary - upper
  • Reticular - lower
  • Dermal papillae - interdigitating
  • Variable thickness - 0.6mm on eyelid; 3mm on hands/feet
• What are the functions of the Dermis?

  • Contain hair and sweat glands - thermoregulation
  • Contain sensory structures - sense e.g. touch
  • Gives structure to skin & hence gives body shape
• Where is the dermis located?

  • Between epidermis & hypodermis
  • AKA corium and with epidermis - cutis
• What causes skin wrinkling?

  • Thinning of the dermis
  • less collagen & elastic fibres
• What is the structure of Epidermis?

  • 4 layers in thin skin:
  • Stratum Corneum
  • Stratum Graunlosum
  • Stratum Spinosum
  • Stratum basale
  • 5 layers in thick skin:
  • Stratum Lucidum
  • Held together by adherents junctions & desmosomes
  • Has some terminal nerve endings
  • No blood vessels
• What type of tissue is epidermis?

  Keratinised Stratified Squamous Epithelium
• What are the functions of the epidermis?

  • Prevent water loss
  • Prevents entry to bacteria & parasites
  • Special cells that present pathogens to immune cells
  • Special cells that give skin its colour
  • Synthesis of keratin
  • Prevents underlying tissue loss due to abrasion
• What is the stratum corneum?

  • Outermost layer made of dead keratinocytes - squames
  • Thick on palms & soles of feet
  • Continuously shed
• What is the stratum lucidum?

  • Layer of epidermis only present on palms & soles of feet
  • Prevents friction between corneum & granulosum
• What is the stratum granulosum?

  • Stratified squamous epithelium
  • Lamellar granules
  • FIlament-associated proteins assembling keratin fibrils
  • Tonofibrils
  • Bundles of keratin filaments and keratohyalin granules - made by lamellar bodies
• What is the stratum spinosum?

  • Cuboidal epithelium arranged in 3 layers held together by desmosomes
  • Produces lamellar bodies (keratohyalin factories & lipid production)
• What is the stratum basale?

  • Tall columnar epithelial cells
  • Constantly renew keratinocytes by cell division
  • As daughter cells differentiate they move away from the epidermis-dermis junction
  • They make keratin filaments(tonofilaments)
  • They lose their ability to divide
  • Also home to melanocytes - produce melanin
• What is a keratinocyte?

  • Cells that synthesise keratins
  • Contribute to the strength of the epidermis
  • Keratins are the main constituents of hair & nail - & horns
  • Normal transit time of keratinocyte from basal layer to stratum corneum is 28-40 days
• What change to keratinocytes occurs in psoriasis?

  • Transit time massively reduced, such that stratum corneum is produced in abundance as silvery scales every 2-3 days or 7-8 days
• What change to keratinocytes occurs in hyperkeratosis?


  • Too much keratin put on surface of skin - hands & feet
• What is the keratinocyte growth pattern?

  1. Stem cell self renewal
  2. Daughter cells differentiate
  3. Crowding forces basal cells away
  4. Spinous cell starts making keratin & laminar bodies
  5. Increased Golgi production & keratin/lipid Secretion - apoptosis
  6. Cells migrate through waterproof layer & die off
  7. Keratin layer thickens
  8. Squames produced
  9. Desquamation occurs
• What is a melanocyte?

  • Mature melanosome containing melanin
  • Transferred to neighbouring keratinocytes by pigment donation
  • Phagocytosis of the tips of the dendritic process
  • Occurs in basal & spinous layers
• What is a langerhans’ cells?


  • Cells derived from bone marrow
  • Part of immune response
  • Macrophage which presents to dendritic cells or T-lymphocytes
  • Part of stratum spinosum
• What are merkel cells?

  • Mechanoreceptor cells associated with sensory nerve endings
• What is the Fitzpatrick skin types scale?


  A classification system used to categorize human skin color and response to sun exposure.

  • I - VI with paler skin having lower denominations.
  • All skin colours susceptible to skin cancer
• What are the 4 types of skin?

  • Hairy skin - tends to be thin
  • Non-hairy skin - tends to be thick
  • Thin skin
  • Thick skin
• Where are skin appendages derived from?

  • Down growths of epidermal epithelium during 3rd month of foetal development
• What are the 3 types of hair?


  • Lanugo - covers developing foetus
  • Vellus hairs - replaces lanugo
  • Short, thin, light coloured & soft
  • Terminal - head, axillae, external genital region
  • Long, wide, dark coloured & coarse
  • Produced by actions of testosterone
• What are the functions of hair?

  • Thermoregulation
  • Hair stands erect when body temperature is lower than normal range
  • Erector pili muscle contracts when stimulated by autonomic nervous system
  • Acts as barrier to UV rays
  • Sexual attraction
  • Hair can be alluring
  • Apocrine sweat glands secrete oils
  • Sensation
  • Hair has sensory nerve endings within bulb
  • Protection
  • Eyelashes & nasal hair prevent dust & pathogens entering body
  • Eyebrows reduce light & sweat entering eyes
  • Axilla hair acts as conduit to conduct sweat away from body
• What is the structure of arrector pili muscle?

  • Smooth muscle fibres attached to papillary region of dermis & hair bulb
• What are sebaceous glands?

  • Holocrine glands that produces sebum
  • Lubricates skin/hair
  • Reduces water loss
  • Aids flexibility
  • Protects the skin & hair from too much moisture
  • Reduces epidermal damage from friction
  • Facilitates the cooling of skin in hot conditions - alongside sweat glands
  • Highest density in face & scalp
  • Part of pilosebaceous unit
• How does skin allow for sensation?

  • End bulbs containing thermoreceptors
  • Free nerve endings have nociceptors
  • Tactile discs - vertical dimpling of skin attaches to basal layer keratinocyte - sense touch, pressure & texture
  • Meissner corpuscle - tapping & flicking movement detected
  • Pacinian corpuscle - vibration/pressure
  • Ruffini’s corpuscle - joint movement
  • Root hair plexus - vibrations in hair shaft
• What is the structure of nails?

  • Only contains alpha keratin
  • Made up of
  • Nail plate
  • Nail matrix
  • Nail bed
  • surrounding grooves
• What is location of nails?

  • Distal surface of phalanges
• What are the functions of nails?

  • Protection of distal phalanx & surrounding soft tissues from injuries
  • Enhances precise delicate movements of the distal digits through counter-pressure exerted on the pulp of the finger
  • Enhancing the sensitivity of the fingertip
  • As a tool - enables so called extended precision grip
  • e.g. Pulling out a splinter
  • Growth rate of nails is correlated with length Of phalanx
• What terminology is used to describe lumps/bumps?

  • Size
  • Papule - <5mm
  • Nodule 5-10mm
  • Contents
  • Small water blister - vesicle
  • Large water blister - Bulla
  • Pus-filled vesicle - Pustule
• What terminology is used to describe redness?

  • Erythema
• What terminology is used to describe flat lesions (superficial changes)

  • Non-palpable area of discolouration - Macule
  • Macule >2cm - Patch
  • Palpable flat topped area > 2cm Plaque
• What terminology is used to describe scratches (superficial changes)?

  • Excoriations
• What terminology is used to describe stretch (superficial changes)?

  • Striae