Exam 3 - Specialized tissues, stem cells, and tissue renewed

Question 1

What are characterisitcs of stem cells?

Answer 1

• Not terminally differentiated
• can divided without limit
• Ability to renew themselves
• when divide each new cell has ability to remain a stem cell or become differentiated into a differentiated cell type
• undergo slow division

Question 2

What totipotency of cell ?

Answer 2

Ability of a cell to give rise to all cells of an organism, including embryonic and extra embryonic tissue

Ex: Zygote

Question 3

what is pluripotency?

Answer 3

Ability of a cell to give rise to all cells of embryo and subsetuently adult tissues

Ex: embryonic stem cells

Question 4

What is a multipotency?

Answer 4

Ability of a cell to give rise to different cell types of given linage

Ex: adult stem cells

Question 5

What asymmetric division?

Answer 5

creates 2 cells, one stem cell characterisitcs and another with ability to differentiate

Question 6

What is independent choice

Answer 6

Is more flexbile explains the sharp increase in stem cell numbers when needed for repair.

Divison makes 2 identical cells but the outcome is stochoastic and/or influenced by environment

Question 7

what are founder cells

Answer 7

• Each organ/tisue has fixed number of founder cell populations programmed to have fixedd number of divisions
• If the adult organ needs to be renewed, the founder stem cells can divide giving rise to one daughter cell that remains a stem cell and a set of cells that a set number of transit amplifying divisons

Question 8

what are transit amplifying cells

Answer 8

• Mixed with stem cells are other cells that divide frequently
• these are called transit amplifying cells
• transit from a cell with stem cell characteristics to a differentiated cell
• They are programmed to divide for a limited number of times
• parts of strategy for growth control

Question 9

What are characteristics of adult stem cells

Answer 9

• Tissue specfic
• Examples: epidermal stem cells, intestinal stem cells, hematopoeitic stem cells, neural stem cells
• Serve as an internal repair system in many tissues dividing without limit to replenish cells that may be damaged
• in some tissues replace cells that have very rapid turnover
• need a specialized microebvironemnt where they can stay as a stem cell (niche)
• both intrinsic and extrinsic factors regulate them

Question 10

What is the architectire of the skin?

Answer 10

• epidermis
  
  • form the outer covering of skin
  • creates a water barrier
  • made of epithelial cells
  • continuously repaired and renewed
• Dermis
  
  • second layer, rich in collagen, provides toughness
• Hypodermis
  
  • fatty subcutaneous layer

Question 11

What are the different cell types of the skin?

Answer 11

• Fibroblasts
  
  • secrete extracellular matrix and provide mechanical support
• Endothelial cells
  
  • lined blood vessels
  • supply nutrients and oxygen and remove waste
• Macrophages and dendritic cells
  
  • provide defense against probes and pathogens
• Lymphocytes
  
  • provide adaptive immune response
• Nerve fibers
  
  • provide sensory information

Question 12

What are layers of the epidermis

Answer 12

• The epidermis is a stratified layer made of keratinocytes
• Deep to superfical
  
  • Basal cell layer
    
    • attached to basal lamina
    • only dividng cells in epidermis
  • Prickle cells
    
    • HAve numerous desmosomes that attach tufts of keratin filaments
  • granular cells
    
    • which are sealled together to formed a waterproof barrier
    • forms a boundary between inner metabolically active strat and outer dead epidermis cells
  • Squame
    
    • outermost layer
    • flatten dead cells densely packed with keratin but no organelles

Question 13

What is the renewel of epidermis by stem cells?

Answer 13

• Cause
  
  • wear adn tear needs constant repair
• What
  
  • basal cells (specificaly STEM CELLS) are dividing
    
    • stem cells provide infinite supply
• Where
  
  • Basal layer has stem cells
• Process
  
  • while basal cells divide
  • others move to layer above it
  • prickle cell then to granular
  • change in gene expression at each layer
    
    • partial degradation where cells lose nucleus and other organelles
• Requirements
  
  • Mixure of cells needed. those that can divide and differentiate and renew worn out cells and those that can remain undifferentiated
  • contact with basal lamina controls number of stem cels
  • maintance of contact preserves stem cell potential acts as an off switch for divison when loss of contact triggers Differentation
  • Proliferative potential of stems cells directly correltaes with express of b1 subunit of Integrin ( helps maintain adhesiton of basal lamina)
    
    • mediated by integrin signaling
• Why?
  
  • helps controls size of stem cell population. To many stem cells can lead to cancer
• Example
  
  • Clusters of cells with high levels of integrin found near the basal lamina andin bulge of hair follicle

Question 14

What are various signinaling pathways in epidermis renewal?

Answer 14

• overactivation of hedgehog pathway makes cell continue to divide even after exit from basal layer
  
  • deficit of hedgehog signal leads to loss of sabaceous glands
• Up regulaton of Wnt Signaling causes extra hair follicles to develope (give rise to tumors) Loss of Wnt signaling leads to failure of Hair follicle development
• Delta Notch signaling restricts size of stem cell population
• lateral inhibition causes neighbors of stem cells become transit amplifying cells
• TGFB plays role in repair of skin wounds promoting formation of collagen rich scar tissue