Specialized Tissues, Stem Cells And Tissue Renewal I

Question 1

Asymmetric division

Answer 1

Creates 2 cells, one with stem cell characteristics and another w/ the ability to differentiate.

Question 2

Independent choice

Answer 2

Division makes 2 identical cells but the outcome is stochastic and/or influenced by environment

Question 3

What are the drawbacks of the asymmetric division theory?

Answer 3

Cannot explain how existing stem cells increase their numbers

Question 4

Why is the independent choice theory favored?

Answer 4

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

Question 5

Founder stem cells

Answer 5

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

Question 6

Explain why stem cells of some tissues selectively retain original DNA

Answer 6

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

Question 7

What type of cells are transit amplifying cells?

Answer 7

Committed

Question 8

Epidermis

Answer 8

Forms outer covering of skin; creates water barrier; made of epithelial cells; continuously repaired and renewed

Question 9

Dermis

Answer 9

Second layer, rich in collegen, provides toughness

Question 10

Hypodermis

Answer 10

Fatty subQ layer

Question 11

ECM is secreted by?

Answer 11

Fibroblasts - gives mechanical support

Question 12

What supplies the skin w/ nutrients and O2 and also removes waste products?

Answer 12

Blood vessels lined w/ endothelial cells

Question 13

What cells of the skin provide defense against microbes and pathogens?

Answer 13

Macrophages and DCs

Question 14

Lymphocytes provided what?

Answer 14

Adaptive immune response

Question 15

Nerve fibers provide what?

Answer 15

Sensory info

Question 16

Epidermis is a _____ layer made of ______

Answer 16

Stratified layer made of keratinocytes. (Have keratin intermediate filaments)

Question 17

Basal cell layer

Answer 17

Attached to basal lamina. These are the only dividing cells in the epidermis.

Question 18

What is the layer above the basal cell layer?

Answer 18

Prickle cells - have numerous desmosomes that attach tufts of keratin filaments

Question 19

What layer is after the prickle cell layer and what is its purpose?

Answer 19

Granular cell layer - sealed together to form a waterproof barrier. It forms a boundary b/w inner metabolically active Strate and outer dead epidermis

Question 20

What is the outermost later of epidermis?

Answer 20

Squame: flattened dead cells densely packed w/ keratin but w/ no organelles.

Question 21

What type of renewal process does the epidermis undergo?

Answer 21

Self-renewing. It experiences constant wear and tear therefore needs constant repair.

Question 22

What happens to cells as the start undergoing partial degradation while moving up through the layers of the epidermis?

Answer 22

They lose their nucleus and other organelles. This is dependent on partial activation of the apoptotic machinery.

Question 23

What is the time from birth of cell in basal layer to shedding from the surface?

Answer 23

1 month

Question 24

What is the function of the stem cells w/I the basal layer?

Answer 24

The divide to maintain the basal layer and also supply cells that move to other layers, undergo change in gene expression and differentiate

Question 25

Where does the hair grow upward from?

Answer 25

The dermal papilla

Question 26

Sebaceous gland secrete?

Answer 26

Sebum

Question 27

The hair follicle undergoes a cycle of what 3 things?

Answer 27

Growth, regression, and reconstruction

Question 28

What are the characteristics and funtions of stem cells in the hair follicle?

Answer 28

They are present in a bulge; they help in reconstruction and give rise to hair follicle and interfollicular epidermis

Question 29

What controls the numbers of stem cells?

Answer 29

Contact w/ basal lamina

Question 30

What preserves stem cell potential?

Answer 30

Maintenance of contact w/ basal lamina

Question 31

Loss of contact of basal lamina trigger what?

Answer 31

Terminal differentiation

Question 32

Proliferative potential of stem cells directly correlates w/ expression of what?

Answer 32

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

Question 33

Transit amplifying cells

Answer 33

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

Question 34

What are factors that govern the renewal of the epidermis?

Answer 34

1. Rate of stem cell division 2. Probability that one of the daughter cells will remain a stem cell 3. Rate of division of the transit amplifying cells 4. Timing of exit from basal layer 5. Time cells takes to differentiate and be sloughed away from surface

Question 35

What is the most important signal that regulates epidermis renewal?

Answer 35

Contact w/ the basal lamina

Question 36

What mediates the signal of contact w/ basal lamina?

Answer 36

Integrin signaling. (Increased integrin means staying in basal layer)

Question 37

Over activation of the hedgehog pathway leads to what?

Answer 37

Makes cell continue to divide even after exit from basal layer

Question 38

Deficit of hedgehog signal leads to what?

Answer 38

Loss of sebaceous glands

Question 39

Up regulation of Wnt signaling causes what?

Answer 39

Extra hair follicles to develop (gives rise to tumors)

Question 40

Loss of Wnt signaling leads to what?

Answer 40

Failure of hair follicle development

Question 41

Notch signaling does what ?

Answer 41

Restricts size of stem cell population

Question 42

Effect of lateral inhibition on neighbors of stem cells?

Answer 42

Causes them to become transit amplifying cells

Question 43

Role of TFGbeta

Answer 43

Repair of skin wounds promoting formation of collagen rich scar tissue

Question 44

What are the characteristics of stem cells?

Answer 44

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.)