Specialized Tissues, Stem Cells and Tissue Renewal

Question 1

Describe the epidermis

Answer 1

Forms the outer covering of the skin
Creates a water barrier
Epithelial cells
Continuously repaired and renewed

Question 2

Describe the dermis

Answer 2

Second layer, rich in collagen, provides toughness

Question 3

Describe hypodermis

Answer 3

Fatty subcutaneous layer

Question 4

What is the extracellular matrix secreted by?

Answer 4

fibroblasts and it provides the mechanical support

Question 5

What are blood vessels lined with?

Answer 5

endothelial cells

Question 6

What provides defense against microbes and pathogens?

Answer 6

Macrophages and DCs

Question 7

What provides adaptive immune response?

Answer 7

lymphocytes

Question 8

The epidermis is a ______ layer made up of ______.

Answer 8

Stratified

Keratinocytes

Question 9

What layer is attached to basal lamina?

Answer 9

Basal cell layer

Question 10

What are the only dividing cells in the epidermis?

Answer 10

Basal cell layer

Question 11

In the epidermis, The strata made of several layers of prickle cells have numerous what?

Answer 11

desmosomes that attach tufts of keratin filaments

Question 12

In the epidermis, the layer with granular cells are sealed together to form what?

Answer 12

Waterproof barrier

Question 13

In the epidermis, what does the granule cell layer form a boundary between?

Answer 13

Inner metabolically active strata and outer dead epidermis cells

Question 14

What is the outermost layer of the epidermis called?

Answer 14

Squame, Flattened dead cells densely packed with keratin but with no organelles

Question 15

Basal cells are ____ cells

Answer 15

dividing

Question 16

While some basal cells divide and maintain the basal cell layers, others do what?

Answer 16

Move to the layers above it

Question 17

What layers above do the basal cells reach?

Answer 17

First prickle cell layer and then granule cell layer

They change in gene expression at each step of differentiation

Question 18

As basal cells migrate to the top of the epidermis, what changes do they undergo?

Answer 18

Start undergoing partial degradation. Cells lose their nucleus and other organelles.
Dependent on partial activation of the apoptotic machinery

Question 19

What cells provide an indefinite supply of fresh differentiated cells?

Answer 19

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

Question 20

The hair follicle is a specialization of the epidermis and the hair grows upward from what?

Answer 20

Dermal papilla (connective tissue)

Question 21

What secretes oily liquids?

Answer 21

Sebaceous glands

Question 22

What is the oily liquid sebaceous glands secrete?

Answer 22

Sebum

Question 23

What cycle does a hair follicle undergo?

Answer 23

Growth, regression, and reconstruction

Question 24

What is present in a bulge to help in reconstruction and gives rise to hair follicle and interfollicular epidermis?

Answer 24

Stem cells

Question 25

What are characteristics of stem cells?

Answer 25

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

Question 26

Stem cells are tissue ______.

Answer 26

specific

Question 27

How is a steady pool of stem cell population accomplished?

Answer 27

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

Question 28

What is the issue with divisional Asymmetry?

Answer 28

Has draw backs | Cannot explain how existing stem cells increase their numbers

Question 29

Why is environmental asymmetry a more plausible theory?

Answer 29

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

Question 30

Contact with what controls the numbers of stem cells?

Answer 30

Basal lamina | *maintenance of contact preserves stem cell potential

Question 31

What does loss of contact of the epidermis with the basal lamina trigger?

Answer 31

terminal differentiation

Question 32

What does proliferative potential of stem cells directly correlate with?

Answer 32

Expression of Beta1 subunit of integrin (helps mediate adhesion to the basal lamina)

Question 33

Clusters of cells with high levels of integrin are found where in the epidermis?

Answer 33

Near the basal lamina and in the bulge of hair follicle

Question 34

Mixed with stem cells are other cells that divide frequently, what are these cells called?

Answer 34

Transit amplifying cells

Question 35

Where do transit amplifying cells transit from?

Answer 35

Transit from A cell with stem cell characteristics to a differentiated cell. Leaves the basal layer and are incorporated into the layers above

Question 36

Can transit amplifying cells divide an unlimited amount of times?

Answer 36

No they are programmed to divide for a limited number of times. Part of a strategy for growth control

Question 37

Each organ/tissue has fixed number of _____ cell populations programmed to have fixed number of divisions

Answer 37

Founder

Question 38

What are founder stem cells controlled by?

Answer 38

Short range signals that operate for a few hundred cell diameters

Question 39

If the adult organ needs to be renewed, Founder stem cells can divide as what?

Answer 39

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

Question 40

What is taken up by cells in the S phase of cell cycle that allows the daughter cell to retain stem cell characteristics?

Answer 40

BrdU label

Question 41

______ cells retain BrdU label for a long time

Answer 41

Stem * could be due to slow rate of division * also could be due to asymmetric segregation of their DNA

Question 42

After division, what happens to the BrdU label?

Answer 42

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

Question 43

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?

Answer 43

Genetic errors in stem cells

Question 44

What are factors governing renewal of epidermis?

Answer 44

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

Question 45

What is the most important signal for regulating of epidermis renewal?

Answer 45

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

Question 46

Overactivation of ______ pathway makes cell continue to divide even after exit from basal layer.

Answer 46

Hedgehog

Question 47

Deficit of hedgehog signal leads to what?

Answer 47

loss of sebaceous glands

Question 48

Up-regulation of ____ signaling causes extra hair follicles to develop (give rise to tumors)

Answer 48

Wnt

Question 49

Loss of Wnt signaling leads to what?

Answer 49

Failure of hair follicle development

Question 50

What restricts size of stem cell population?

Answer 50

Notch signaling

Question 51

Lateral inhibition causes neighbors of stem cells to become what?

Answer 51

Transit amplifying cells

Question 52

What plays a key role in repair of skin wounds promoting formation of collagen rich scar tissue?

Answer 52

TFGBeta