LAYERS ANF ACCESSORY ORGANS OF THE SKIN

• Epidermis


  Consists of keratinized stratified squamous epithelium
• Cell types present in the epidermis

  • Keratinocytes
  • Melanocytes
  • Langerhans cells
  • Merkel cells
• Keratinocytes


  Produce keratin, a protein that hardens and waterproofs the skin
• Melanocytes


  Produce melanin, a pigment that protects cells from ultraviolet radiation
• Langerhans cells


  Phagocytic macrophages that interact with white blood cells during an immune response
• Merkel cells


  Form Merkel discs, which serve a sensory function
• Layers of the epidermis

  • Stratum Corneum
  • Stratum Lucidum
  • Stratum Granulosum
  • Stratum Spinosum
  • Stratum Basale
• Stratum Corneum


  Contains many layers of dead, anucleate keratinocytes completely filled with keratin
• Stratum Lucidum


  Contains two to three layers of anucleate cells, found only in thick skin
• Stratum Granulosum


  Contains two to four layers of cells held together by desmosomes, contributing to keratin formation
• Stratum Spinosum


  Contains eight to ten layers of cells connected by desmosomes, moderately active in mitosis
• Stratum Basale


  Contains a single layer of columnar cells actively dividing by mitosis
• Dermis


  The second layer of the skin consisting of various connective tissues
• Hypodermis


  Subcutaneous layer consisting mostly of adipose tissue
• Dermis


  • Provides strength
  • Extensibility
  • Elasticity
• Layers of the dermis

  • Papillary layer
  • Reticular layer
• Papillary layer


  A thin outer layer of areolar connective tissue with dermal papillae
• Reticular layer


  A thick layer of dense irregular connective tissue
• Accessory organs of the skin

  • Hairs
  • Nails
  • Sudoriferous glands
  • Sebaceous glands
• Hair


  Elongated filaments of keratinized epithelial cells
• Hair Shaft


  The portion of the hair that is visible on the surface of the skin
• Hair Root


  The portion of the hair that penetrates the skin
• Hair Follicle


  The sheath that surrounds the hair in the skin
• Bulb


  The base of the hair follicle
• Matrix


  The bottom of the hair follicle where cells are actively dividing
• Arrector Pili


  A smooth muscle attached to the hair follicle that causes hair to become erect
• Nails


  Keratinized epithelial cells
• Lunula


  The semilunar lighter region of the nail, area of new nail growth
• Kinds of sudoriferous glands

  • Merocrine (eccrine) glands
  • Apocrine glands
  • Ceruminous glands
  • Mammary glands
• Merocrine (eccrine) glands


  Secrete a watery solution through pores to cool the skin
• Apocrine glands


  Secrete a viscous solution in response to stress or sexual excitement
• Ceruminous glands


  Secrete cerumen (earwax) into the external ear canal
• Mammary glands


  Produce milk that is secreted through the nipples
• Sebaceous (oil) glands


  Secrete sebum, an oily substance that inhibits bacterial growth