Specialized Tissues, Stem Cells And Tissue Renewal I Flashcards
Asymmetric division
Creates 2 cells, one with stem cell characteristics and another w/ the ability to differentiate.
Independent choice
Division makes 2 identical cells but the outcome is stochastic and/or influenced by environment
What are the drawbacks of the asymmetric division theory?
Cannot explain how existing stem cells increase their numbers
Why is the independent choice theory favored?
It is more flexible; it explains the sharp increase in stem cell numbers when needed for repair. Environment may influence batches of cells and doesn’t have to be 50:50 for every division
Founder stem cells
A population of cells programmed to have a fixed number of divisions; each organ has a fixed number of these cells; controlled by short range signals that operate for a few hundred cell diameters; define the size of large final structures
Explain why stem cells of some tissues selectively retain original DNA
BrdU label is taken up by cells in S phase; stem cells retain BrdU for long time; could be due to slow rate of division; or due to asymmetric segregation of their DNA; after division one of the daughter cells gets all the original DNA strands from all the chromosomes making that cell retain stem cell characteristics. Preserved from generation to generations; 2nd cells get newly synthesized strand. This is a way to prevent genetic errors in stem cells
What type of cells are transit amplifying cells?
Committed
Epidermis
Forms outer covering of skin; creates water barrier; made of epithelial cells; continuously repaired and renewed
Dermis
Second layer, rich in collegen, provides toughness
Hypodermis
Fatty subQ layer
ECM is secreted by?
Fibroblasts - gives mechanical support
What supplies the skin w/ nutrients and O2 and also removes waste products?
Blood vessels lined w/ endothelial cells
What cells of the skin provide defense against microbes and pathogens?
Macrophages and DCs
Lymphocytes provided what?
Adaptive immune response
Nerve fibers provide what?
Sensory info
Epidermis is a _____ layer made of ______
Stratified layer made of keratinocytes. (Have keratin intermediate filaments)
Basal cell layer
Attached to basal lamina. These are the only dividing cells in the epidermis.
What is the layer above the basal cell layer?
Prickle cells - have numerous desmosomes that attach tufts of keratin filaments
What layer is after the prickle cell layer and what is its purpose?
Granular cell layer - sealed together to form a waterproof barrier. It forms a boundary b/w inner metabolically active Strate and outer dead epidermis
What is the outermost later of epidermis?
Squame: flattened dead cells densely packed w/ keratin but w/ no organelles.
What type of renewal process does the epidermis undergo?
Self-renewing. It experiences constant wear and tear therefore needs constant repair.
What happens to cells as the start undergoing partial degradation while moving up through the layers of the epidermis?
They lose their nucleus and other organelles. This is dependent on partial activation of the apoptotic machinery.
What is the time from birth of cell in basal layer to shedding from the surface?
1 month
What is the function of the stem cells w/I the basal layer?
The divide to maintain the basal layer and also supply cells that move to other layers, undergo change in gene expression and differentiate
Where does the hair grow upward from?
The dermal papilla
Sebaceous gland secrete?
Sebum
The hair follicle undergoes a cycle of what 3 things?
Growth, regression, and reconstruction
What are the characteristics and funtions of stem cells in the hair follicle?
They are present in a bulge; they help in reconstruction and give rise to hair follicle and interfollicular epidermis
What controls the numbers of stem cells?
Contact w/ basal lamina
What preserves stem cell potential?
Maintenance of contact w/ basal lamina
Loss of contact of basal lamina trigger what?
Terminal differentiation
Proliferative potential of stem cells directly correlates w/ expression of what?
Beta 1 subunit of integrin (helps mediate adhesion to basal lamina). There are clusters of cells w/ high levels of integrin found near basal lamina and in budge of hair follicle
Transit amplifying cells
Divide frequently; from a cell w/ stem cell characteristics to a differentiated cell; leave the basal layer and are incorporated into the layers above. Programmed to divide for a limited number of times. Part of strategy for growth control
What are factors that govern the renewal of the epidermis?
- Rate of stem cell division
- Probability that one of the daughter cells will remain a stem cell
- Rate of division of the transit amplifying cells
- Timing of exit from basal layer
- Time cells takes to differentiate and be sloughed away from surface
What is the most important signal that regulates epidermis renewal?
Contact w/ the basal lamina
What mediates the signal of contact w/ basal lamina?
Integrin signaling. (Increased integrin means staying in basal layer)
Over activation of the hedgehog pathway leads to what?
Makes cell continue to divide even after exit from basal layer
Deficit of hedgehog signal leads to what?
Loss of sebaceous glands
Up regulation of Wnt signaling causes what?
Extra hair follicles to develop (gives rise to tumors)
Loss of Wnt signaling leads to what?
Failure of hair follicle development
Notch signaling does what ?
Restricts size of stem cell population
Effect of lateral inhibition on neighbors of stem cells?
Causes them to become transit amplifying cells
Role of TFGbeta
Repair of skin wounds promoting formation of collagen rich scar tissue
What are the characteristics of stem cells?
Not terminally differentiated; can divide w/o limit; undergo slow division; when divide, give rise to 1 cells w/ stem cell characteristics and the other w/ the ability to be differentiated. Stem cells are tissue specific (epidermal stem cells, intestinal stem cells, etc.)
