Specialized Tissues, Stem Cells and Tissue Renewal Flashcards
Describe the epidermis
Forms the outer covering of the skin
Creates a water barrier
Epithelial cells
Continuously repaired and renewed
Describe the dermis
Second layer, rich in collagen, provides toughness
Describe hypodermis
Fatty subcutaneous layer
What is the extracellular matrix secreted by?
fibroblasts and it provides the mechanical support
What are blood vessels lined with?
endothelial cells
What provides defense against microbes and pathogens?
Macrophages and DCs
What provides adaptive immune response?
lymphocytes
The epidermis is a ______ layer made up of ______.
Stratified
Keratinocytes
What layer is attached to basal lamina?
Basal cell layer
What are the only dividing cells in the epidermis?
Basal cell layer
In the epidermis, The strata made of several layers of prickle cells have numerous what?
desmosomes that attach tufts of keratin filaments
In the epidermis, the layer with granular cells are sealed together to form what?
Waterproof barrier
In the epidermis, what does the granule cell layer form a boundary between?
Inner metabolically active strata and outer dead epidermis cells
What is the outermost layer of the epidermis called?
Squame, Flattened dead cells densely packed with keratin but with no organelles
Basal cells are ____ cells
dividing
While some basal cells divide and maintain the basal cell layers, others do what?
Move to the layers above it
What layers above do the basal cells reach?
First prickle cell layer and then granule cell layer
They change in gene expression at each step of differentiation
As basal cells migrate to the top of the epidermis, what changes do they undergo?
Start undergoing partial degradation. Cells lose their nucleus and other organelles.
Dependent on partial activation of the apoptotic machinery
What cells provide an indefinite supply of fresh differentiated cells?
Stem cells
They replace and renew old cells
The basal layer has stem cells
*they divide to maintain the basal layer and also supply cells to the other layers
The hair follicle is a specialization of the epidermis and the hair grows upward from what?
Dermal papilla (connective tissue)
What secretes oily liquids?
Sebaceous glands
What is the oily liquid sebaceous glands secrete?
Sebum
What cycle does a hair follicle undergo?
Growth, regression, and reconstruction
What is present in a bulge to help in reconstruction and gives rise to hair follicle and interfollicular epidermis?
Stem cells
What are characteristics of stem cells?
Not terminally differentiated
Can divide without limit
Undergo slow division
When it divides it gives rise to 1 cell with stem cell characteristics and the other with the ability to be differentiated
Stem cells are tissue ______.
specific
How is a steady pool of stem cell population accomplished?
Divisional Asymmetry-asymmetric division may create 2 cells, one with stem cell characteristics and another with the ability to differentiate
Environmental Asymmetry - Division makes 2 identical cells but environment may influence/alter 1 cell
What is the issue with divisional Asymmetry?
Has draw backs
Cannot explain how existing stem cells increase their numbers
Why is environmental asymmetry a more plausible theory?
It is more flexible. Explains the sharp increase in stem cell numbers when needed for repair
Environment may influence batches of cells and does not have to be 50:50 for every division
Contact with what controls the numbers of stem cells?
Basal lamina
*maintenance of contact preserves stem cell potential
What does loss of contact of the epidermis with the basal lamina trigger?
terminal differentiation
What does proliferative potential of stem cells directly correlate with?
Expression of Beta1 subunit of integrin (helps mediate adhesion to the basal lamina)
Clusters of cells with high levels of integrin are found where in the epidermis?
Near the basal lamina and in the bulge of hair follicle
Mixed with stem cells are other cells that divide frequently, what are these cells called?
Transit amplifying cells
Where do transit amplifying cells transit from?
Transit from A cell with stem cell characteristics to a differentiated cell. Leaves the basal layer and are incorporated into the layers above
Can transit amplifying cells divide an unlimited amount of times?
No they are programmed to divide for a limited number of times. Part of a strategy for growth control
Each organ/tissue has fixed number of _____ cell populations programmed to have fixed number of divisions
Founder
What are founder stem cells controlled by?
Short range signals that operate for a few hundred cell diameters
If the adult organ needs to be renewed, Founder stem cells can divide as what?
as stem cells giving rise to one daughter cell that remains a stem cell and a set of cells that have a set number of transit amplifying divisions
What is taken up by cells in the S phase of cell cycle that allows the daughter cell to retain stem cell characteristics?
BrdU label
______ cells retain BrdU label for a long time
Stem
- could be due to slow rate of division
- also could be due to asymmetric segregation of their DNA
After division, what happens to the BrdU label?
One of the daughter cells gets ALL the original DNA strands from the chromosomes including the BrdU label and this daughter cell will retain stem cell characteristics
The original strand of DNA is preserved in stem cells from generation to generation. Second cell gets the newly synthesized strand. This is a way to prevent what?
Genetic errors in stem cells
What are factors governing renewal of 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 and the time the cell takes to differentiate and be sloughed away from surface
What is the most important signal for regulating of epidermis renewal?
Contact with basal lamina most important signal
Mediated via integrin signaling
Helps control size of stem cell population
Loss of contact abolishes stem cell characteristics and promotes formation of cells that can become differentiated
Overactivation of ______ pathway makes cell continue to divide even after exit from basal layer.
Hedgehog
Deficit of hedgehog signal leads to what?
loss of sebaceous glands
Up-regulation of ____ signaling causes extra hair follicles to develop (give rise to tumors)
Wnt
Loss of Wnt signaling leads to what?
Failure of hair follicle development
What restricts size of stem cell population?
Notch signaling
Lateral inhibition causes neighbors of stem cells to become what?
Transit amplifying cells
What plays a key role in repair of skin wounds promoting formation of collagen rich scar tissue?
TFGBeta
