WEEK 9

• What is the largest single organ in the body?

  Skin
• What percentage of total body weight does skin typically account for?

  15-20%
• What are the two main layers of the skin?

  Epidermis and dermis
• What is the origin of the epidermis?

  Ectodermal origin
• What is the role of dermal papillae?

  Strengthen adhesion between dermis and epidermis
• What are some derivatives of the epidermis?

  Hairs, nails, sebaceous and sweat glands
• What is the function of the subcutaneous tissue?

  Contains pads of adipocytes
• What are the main functions of the skin?

  • Protection
  • Sensory
  • Thermoregulatory
  • Metabolic
  • Sexual signaling
• What type of skin covers the palms and soles?

  Thick skin
• What type of skin covers the rest of the body?

  Thin skin
• What type of epithelium is the epidermis made of?

  Keratinized stratified squamous epithelium
• What percentage of the epidermis is made up of keratinocytes?

  85-95%
• What is the function of keratinocytes?

  Produce keratin
• What happens to keratinocytes near the surface of the skin?

  They become dead cells and slough off
• What percentage of the epidermis is made up of melanocytes?

  7-10%
• What is the role of melanocytes?

  Produce melanin pigment
• What causes skin color to vary?

  Melanin
• What are the two forms of melanin?

  Pheomelanin and eumelanin
• Where are melanocytes most plentiful?

  In the epidermis of specific areas
• What is a nevus?

  A benign localized overgrowth of melanocytes
• What is albinism?

  An inability to produce melanin
• What enzyme is often missing in albinos?

  Tyrosinase
• What are the effects of albinism on the skin?

  Increased risk of sunburn and vision problems
• What is vitiligo?

  Loss of melanocytes producing white spots
• What is cyanosis?

  Blue discoloration due to low oxygen
• What is jaundice?

  Yellow discoloration due to liver disease
• What is erythema?

  Redness due to capillary obstruction
• What percentage of the total cell population do Langerhans cells comprise?

  2-8%
• What is the function of Langerhans cells?

  Act as antigen-presenting cells
• What are Merkel cells also known as?

  Epithelial tactile cells
• What is the role of Merkel cells?

  Essential for light touch sensation
• What is the stratum basale also known as?

  Basal layer
• What characterizes the stratum basale?

  Intense mitotic activity
• What is the stratum spinosum known for?

  Being the thickest layer of the epidermis
• What do keratinocytes in the stratum spinosum do?

  Synthesize keratins
• How many rows of flattened keratinocytes are in the stratum granulosum?

  Three to five rows
• What is keratohyalin's role in the stratum granulosum?

  Converts keratin intermediate filaments into keratin
• What is the stratum lucidum present in?

  Skin of fingertips, palms, and soles
• What characterizes the stratum corneum?

  Contains dead, flat keratinocytes
• What is the thickness of the dermis?

  Varies, maximum of 4 mm on the back