31. Stem Cells And Tissue Renewal Flashcards
Are stem cells tissue specific?
Yes
How are stem cells maintained throughout the life of an organism?
- Asymmetric division
2. Independent choice
How can asymmetric division provide stem cells teh ability to maintain through out a lifetime?
2 cells are created. One has stem cell characteristics and the other has the ability to differentiate
How can independent choice provide stem cells the ability to maintain existence throughout lifetime?
The division has 2 identical cells for but the outcome is influenced by the environment
What is one drawback of teh asymmetric division theory of stem cell proliferation?
Unable to explain how stem cells rapidly increase their numbers
Why is the independent choice more highly supported as the theory for stem cell proliferation?
More flexible and more able to explain the rapid increase of stem cells. The environment can influence how many cells are able to differentiate or remain as stem cells
What are founder stem cells?
Cells in a tissue with a fixed number of founder stem cells that are programmed to undergo a set number of divisions
What ultimately controls the size of a final structure?
The number of founder stem cells present in that tissue.
What is a unique feature of the founder stem cells?
- They are established early in development.
- Have a set number in each tissue that will grow and divide for a finite amount of time until they reach/fulfill the size of their final structure
Why do stem cells retain BrdU label and when is this label taken into the cell??
- Retain due to slow division rate
2. Taken into the cell during S phase of cell cycle
What is the epidermis?
- Outer skin layer
- Water barrier
- Epithelial cells. Continuously repaired and renewed
What is the dermis?
2m layer of collagen, provides toughness to skin
What is the hypodermis?
Fatty SubQ layer
What provides teh skin with mechanical support?
Extracellular matrix secreted by the fibroblasts
What components of the skin remove waste products?
Blood vessels and endothelial cells
Which cells provide defense against microbes and pathogens?
Dendritic cells and macrophages
What cells form the epidermis?
Stratified keratinocytes
What are the only dividing cells located in the epidermis?
The basal cell layer, which are attached to the basal lamina
What are the layers of cells from deep to superficial?
- Basal lamina
- Basal cell layer
- Prickle cell layer
- Granular cell layer
5 keratinized squamous epithelium
What are teh characteristic features of prickle cells?
Multiple desmosomes that attach tufts of keratin filaments
What is characteristic of the granular cells?
Seal together to form the waterproof barrier
What boundary do teh granular cells form?
Boundary between the inner metabolically active strata and the dead epidermis
What is the outermost layer of epidermis?
Squame: flattened dead cells packed with keratin but no organelles
What are the characteristics of stem cells?
- Not terminally differentiated
- Divide without limits
- Undergo slow division
- Provides one stem cell and one with ability to differentiate
How does the epidermis renew itself?
Basal cells divide to produce new basal cells, and other cells that will migrate superficially to replace the cells from inside out
How often are the epidermis cells replaced?
Once every month
What controls the rate/initiation of basal cell division and differentiation?
- Contact with basal lamina via beta-integrins prevents the differentiation of the basal cells.
- Reduced beta-integrin contact allows basal cells to divide and differentiate
Where does a hair follicle grow up from?
- Dermal papilla
What is sebum?
- Oily liquid secreted from the sebaceous gland
What is the specific integrin that prevents stem cell differentiation while in contact?
Beta-1 integrin subunit
Where do transit amplifying cells come from?
Basal layer and incorporate into higher layers
What cells have finite division but originate in the basal layer and migrate to higher levels?
- Transit amplifying cells
What are transit amplifying cells used for?
To control growth
What are the factors that control the rate of epidermis renewal?
- Rate of stem cell division
- Rate of transit amplifying cells division
- Migration rate from basal layer to differentiated state
What is the single most important signal for controlling epidermis renewal?
- Contact with the basal lamina, via beta-1 integrin.
What happens if a signaling pathway is disrupted within the epidermis renewal system?
- Increase chances of epidermal cancer development
What happens if the hedgehog pathway becomes overactive?
- Cells continue to divide after leaving the basal layer. Overproduction of improper cells
What happens if sonic hedgehog is deficient to the epidermal layer?
- Reduced function or presence of sebaceous glands
What happens when Wnt-signaling is overactive during epidermis renewal?
- Extra hair follicle develop, can form tumors
What happens when Wnt-signaling is underproduced in the epidermal signaling pathways?
- No hair follicle development
What happens if Notch signaling is too high in the epidermal renewal?
Stem cell population will be dramatically decreased
What happens if Notch is released in too low amounts?
Stem cell population is not inhibited and can overgrow=> tumor growth
What is the signaling molecule that promotes skin wound repair by forming a collagen rich scar?
- TGF-beta
What is the role of TGF-beta in the epidermal renewal pathway?
Promotes skin wound repair.
What is the role of Wnt signaling pathway?
Controls the formation of hair follicles.
What is the role of sonic hedgehog in terms of epidermal renewal pathways?
- Controlling the sebaceous gland formation.
