Epidermis Cells and Layers

Question 1

describe keratinocytes

Answer 1

• predominant cell type
• originate in the SB
• attached to each other by desmosomes and to basal lamina by hemidesmosomes
• sequentially move through the layers continually producing:
  
  • keratins
  • lamellar bodies
• undergo programmed cell death

Question 2

describe melanocytes

Answer 2

• neural crest derived - dendritic cells
• found only in the basal layer
  
  • no desmosomal connections but are attached to the basal lamina via hemidesmosome like structures
• retain their ability to replicate throughout their life
• produce melanin that is transferred to surrounding kertinocytes (melanocytes themselves appear CLEAR)
  
  • cytocrine secretion
    
    • UV protection

Question 3

Answer 3

• EM of melanocyte
• melanocyte to keratinocyte ratio is constant between all races (different among body parts)
  
  • skin color - amount of melanin, not melanocytes
• oxidation of tyrosine –> DOPA –> melanin
  
  • large Golgi in melanocytes

Question 4

why more melanin in stratum basale?

Answer 4

• more melanin in SB because that’s where the stem cells are
  
  • protect the keratinocytes
• the melanocytes don’t have melanin protecting its nucleus
  
  • can lead to a melanoma
    
    • normal nevus = mole
    • malignant melanoma

Question 5

describe Merkel’s cells

Answer 5

• least numerous - dendritic cells
• located in stratum basale
• detect touch sensations
  
  • most abundant in skin where sensory perception is acute (fingertips)
• have desmosomes (want to remain in place)
• cytoplasm contains neurosecretory granules

Question 6

Answer 6

• EM of Merkel’s cells
• cytoplasm has neurosecretory granules since it is involved in acute touch sensation

Question 7

describe Langerhans cells

Answer 7

• Immunological function
  
  • encouter, process and express antigens
  • antigen presenting cells (APC)
  • migrate to the lymph node to present the antigen to T-lymphocytes (NO desmosomes)
    
    • therefore involved in delayed-type hypersensitivity reactions
• nucleus basophilic because it is very active

Question 8

Answer 8

• TEM of Langerhans cell
• large nucleus
• possess tennis racquet shaped birbeck granules
  
  • appear as rods (the arrows)
• express both MCH I and MHC II and receptors for IgG

Question 9

describe the stratum basale

Answer 9

• single layer of cuboidal cells
  
  • keratinocyte stem cells (stratum germinativum)
  • melanocytes
  • Merkel cells
• less cytoplasm since more closely packed nuclei
  
  • intensely basophilic
  • contains many melanin granules
• provides for epidermal cell renewal
• rests on the basal lamina
  
  • attached by hemidesmosomes
• extensive cell junctions
  
  • desmosomes

Question 10

Answer 10

• image is stratum basale
  
  • single layer of cuboidal cells
• intensely basophilic
• contains many melanin granules

Question 11

describe the stratum spinosum

Answer 11

• several cell layers thick
• cells are larger than those in the stratum basale
• gradually change their appearance as they move closer to the surface
• exhibit numerous cytoplasmic processes of spines
  
  • prickle layer
• processes of adjacent cells are connected to each other via desmosomes
  
  • appears as a slight thickening and is known as the node of bizzozero

Question 12

Answer 12

• stratum spinosum
  
  • many layers of cells above the single layer SB
• exhibit numerous cytoplasmic processes of spines, aka prickle layer
  
  • this is the cell junction/desmosomes

Question 13

describe the stratum granulosum

Answer 13

• most superficial of the non keratinized cells
• varies from 1 to 3 cell layers thick
• contain conspicuous granules which give them a granulated appearance
  
  • keratohyalin granules
    
    • stain intensely basophilic
    • make precursor for fillagrin (which organizes the keratin)
    • responsible for aggregating the kertain filaments within the cornified cells
  • Lamellar bodies
    
    • epidermal water barrier

Question 14

Answer 14

• a = keratohyalin granules (KG) and lamellar bodies (arrowheads)
• b = lamellar body

Question 15

describe the formation of the epithelial water barrier

Answer 15

• cell envelope
  
  • insoluble proteins on inside of cell membrane
  • mechanical part of barrier
• lipid envelope
  
  • lipid layer on outer surface of the cell membrane
  • Lamellar bodies
    
    • formed by the Golgi of the spinosum cells
    • contents secreted by exocytosis

Question 16

describe the stratum lucidum

Answer 16

• only in thick skin
• appears to contain cells in which the keratinization process is well advanced

Question 17

describe the stratum corneum

Answer 17

• several layers of dead keratinocytes
  
  • no organelles or nuclei
  • deeper portion of the layer contains the water barrier
• filled with keratin filaments aggregated into tonofibrils
• abrupt transition from granulosum

Question 18

describe the process of keratinization

Answer 18

• cells lose their organelles, cytoplasm and nuclei
• more tonofilaments are formed
• tonofilaments arranged into fibrils by fillagrin
• when it reaches the upper layers of the stratum corneum the desmosomes are broken apart
• cells are sloughed off

Question 19

describe psoriasis

Answer 19

• high turnover of kertinocytes
• cells that shouldn’t be exposed are exposed
• mild forms on scalp forms dandruff

Question 20

describe epidermal and dermal ridges

Answer 20

• areas that are subject to increased mechanical stress the epidermal ridges are much deeper and the dermal papillae are much longer and more closely spaced creating a more extensive interface between the dermis and epidermis