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Molecular & Cell Biology > specialized tissues, stem cells and tissue renewal > Flashcards

specialized tissues, stem cells and tissue renewal Flashcards

1
Q

what are stem cells

A

unspecialized cells

capable of renewing themselves

can be induced to differentiate into tissue or organ specific cells with specialized functions

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2
Q

what organs do stem cells regularly divide to repair and replace worn-out or damaged tissues

A

gut, bone marrow, and skin

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3
Q

what organs do stem cells only divide under special conditions

A

pancreas, brain, and heart

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4
Q

characteristics of stem cells

A

not terminally differentiated

can divide without limit

able to renew themselves (preventing depletion of stem cells)

undergo slow division

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5
Q

totopotency

A

ability of a cell to give rise to all cells of an organism, including embryonic and extra-embryonic tissues (placenta)

e.g. zygote

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6
Q

pluripotency

A

ability of a cell to give rise to all cells of the embryo and subsequently adult tissues

e.g. embryonic stem cells

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7
Q

multipotency

A

ability of a cell to give rise to different cell types of a given lineage

e.g. adult stem cells

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8
Q

two theories of how stem cell population is maintained

A

asymmetric division

independent choice

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9
Q

asymmetric division

A

creates 2 cells, one with stem cell characteristics and another with the ability to differentiate (due to presence of determinate in cytosol in original stem cell)

first round of division: 50/50 split

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10
Q

independent choice

A

division makes 2 identical cells but the outcome is random and/or influenced by environment (not 50/50 split but depends on the needs of the cell)

first round of division: 50/50 split; or both stem cells; or both differentiated cells

e. g. if everything in cell/tissue is good –> independent choice allows for both daughter cells to become stem cells
e. g. if tissue is injured –> independent choice allows for both daughter cells to become differentiated

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11
Q

asymmetric division cannot explain

A

how existing stem cells rapidly increase their numbers

e.g. doesn’t explain injury situation

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12
Q

internal signals that influence differentiation of stem cells

A

gene expression

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13
Q

external signals that influence differentiation of stem cells

A

microenvironment

  • chemicals secreted by neighboring cells
  • physical contact with neighboring cells
  • stem cell - stem cell interaction
  • molecules in the microenvironment: extracellular matrix; growth factors; oxygen tension; ionic strength; pH; metabolites like ATP
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14
Q

founder stem cells

A

each organ/tissue has fixed number of founder stem cell populations programmed to have fixed number of divisions

founder stem cells divide and give rise to one daughter cell that remains a stem cell and a set of cells that have a set number of transit amplifying divisions

define the size of large final structures

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15
Q

transit amplifying cells

A

transit from a cell with stem cell characteristics to a differentiated cell

programmed to divide for a limited number of times

strategy for growth control

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16
Q

adult stem cells

A

are tissue specific

multipotent

serve as an internal repair system (divide without limit to replenish damaged cells)

need a specialized microenvironment where they can stay as a stem cell

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17
Q

epidermis

A

outer covering of skin

creates a water barrier

made of epithelial cells

continuously repaired and renewed every 30 days

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18
Q

dermis

A

second layer of skin

rich in collagen

provides toughness

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19
Q

hypodermis

A

deepest layer of skin

fatty subcutaneous layer

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20
Q

outer layer of dermis

inner layer of dermis

A

loose connective tissue

dense connective tissue

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21
Q

fibroblasts

A

secrete extracellular matrix providing mechanical support

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22
Q

blood vessels of skin are lined with

A

endothelial cells

blood vessels function to supply nutrients and oxygen and remove waste products

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23
Q

innate immune cells in skin

A

macrophages and dendritic cells provide defense against microbes and pathogens

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24
Q

lymphocytes in skin provide

A

adaptive immune response

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25
Q

cells found in epidermis

A

keratinocytes

melanocytes

dendritic cells (langerhans)

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26
Q

cells found in loose connective tissue of dermis

A

macrophages

fibroblasts

collagen fibers

lymphocytes

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27
Q

cells found in dense connective tissue of dermis

A

fibroblasts

collagen fibers

elastic fibers

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28
Q

epidermis is a _____ layer made of _____

A

stratified

keratinocytes

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29
Q

basal cell layer is attached to

A

basal lamina which separates epidermis from dermis

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30
Q

basal cells are only ____ cells in epidermis

A

dividing/stem

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31
Q

prickle cells

A

have numerous desmosomes that attach tufts of keratin filaments

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32
Q

granular cells

A

last layer of cells that are metabolically active

sealed together to form a waterproof barrier

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33
Q

granular cell layer forms boundary between

A

inner metabolically active strata and outer dead epidermis cells

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34
Q

squame cells

A

flattened dead cells densely packed with keratin but with no organelles

slough off

35
Q

cell layer of epidermis from basal lamina outward

A

basal lamina –> basal cell layer –> prickle cell layer –> granular cell layer –> keratinized squames

36
Q

what is responsible for cell differentiation during renewal of epidermis? (cells changing from one layer to the next)

A

change in gene expression

37
Q

basal layer has stem cells that

A

divide to maintain the basal layer and also supply cells that move to other layers by undergoing change in gene expression

38
Q

what triggers cell differentiation in stem cells of epidermis

A

loss of contact with basal lamina

mediated via integrin signaling

39
Q

what protein assists with stem cell adhesion to basal lamina

A

Beta1 subunit of integrin

when cells loss contact with basal lamina –> integrin expression decreases

40
Q

what factors govern renewal of epidermis

A

rate of stem cell division

probability that one of the daughter cells will remain a stem cell

rate of division of transit amplifying cells

timing of exit from basal layer and the time the cell takes to differentiate and be sloughed away from the surface

41
Q

hair grow upwards from

A

dermal papilla

42
Q

sebaceous glands secrete

A

oily liquid called sebum that nourishes developing hair follicle and hair itself

43
Q

hair follicle undergoes cycle of

A

growth, regression, and reconstruction

44
Q

where are stem cells found in hair follicle

45
Q

overactivation of hedgehog pathway

A

epidermal cells continue to divide even after exit from basal layer

46
Q

underactivation of hedgehog pathway

A

results in loss of sebaceous glands

e.g. baldness

47
Q

overactivation of Wnt signaling pathway

A

causes extra hair follicles to develop (gives rise to tumors)

48
Q

underactivation of Wnt signaling pathway

A

leads to failure of hair follicle development

e.g. baldness

49
Q

notch signaling

A

restricts size of stem cell population

e.g. cell that develops delta protein becomes dominant and inhibits surrounding cells from developing delta protein and instead develops notch receptor –> lateral inhibition

50
Q

TGFBeta pathway

A

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

51
Q

specialized epithelium covers certain parts of the body:

A

nose, ears, and eyes

52
Q

sensory cells present in the sensory epithelium act as _____ converting signals from the environment into an electrical form that can be interpreted by CNS

A

transducers

53
Q

eyes have _____
ears have _____
nose has _____

A

photoreceptors

auditory hair cells

olfactory sensory neurons

54
Q

apical end of sensory neurons

A

detects the external stimulus and converts it into a change in membrane potential

e.g. dendrite

55
Q

basal end of sensory neurons

A

makes a synapse with neurons that relay the sensory information to specific sites in the brain

e.g. axon

56
Q

olfactory neurons are replaced every

57
Q

olfactory neuron’s equivalent to dendrites

A

modified cilia (6-8 per neuron)

58
Q

olfactory neuronal axon transmits information to

A

olfactory bulb in brain

59
Q

supporting cells among olfactory neurons

A

hold neurons in place and separate them from one another

60
Q

olfactory system stem cell

A

basal cell

61
Q

humans have ____ odorant receptor genes whereas dogs have _____

62
Q

olfactory receptors work via what receptor pathway

63
Q

each olfactory neuron expresses only one gene enabling the cell to respond to

A

only one class of odorant

64
Q

what feature of odorant is recognized by olfactory receptor

A

structural

65
Q

a single olfactory receptor can bind to

A

a single class of odorant molecules

66
Q

activated olfactory receptor activates

A

an intracellular G-protein (Golf)

67
Q

Golf alpha subunit activates

A

adenylate cyclase produces cAMP which opens ion channels resulting in influx of sodium and calcium

68
Q

influx of positive ions on olfactory neuron

A

generates an action potential

69
Q

axon of neuron from same gene _____ and synapse together at same point in olfactory bulb (same glomerulus)

70
Q

relay station in brain for olfactory sense

A

glomeruli in olfactory bulb

71
Q

how many glomeruli/bulb in mouse brain

72
Q

neural stem cells residing among the _____ in the olfactory epithelium generate replacements for the lost neurons

A

basal cells

73
Q

when olfactory basal stem cells lose contact with basal lamina, cells

A

divide and differentiate into olfactory neurons

74
Q

regernation of olfactory receptor cells is one of the only few instances of ______ in the CNS

A

adult neurogenesis

75
Q

where are stem cells found in the brain

A

ventricles of forebrain

hippocampus

these stem cells can divide and produce neurons and glial cells

76
Q

stem cells in ventricles migrate

A

to the olfactory bulb where they differentiate into olfactory neurons

77
Q

stem cells in hippocampus

A

involved in learning and memory

about 1400 fresh neurons are generated everyday

78
Q

experimental evidence for neural stem cells

A

neurospheres in medium A: (clusters of stem cells from ventricles and fetal brain) can grow into more stem cells –> transferred to medium B: dissociate and culture as monolayer –> transferred to medium C: cells differentiate into neurons and/or glial cells

79
Q

what factors activates quiescent stem cell proliferation (neurogenesis in brain )

A
  • learning
  • antidepressants (norepinephrine)
  • electrical stimulation (deep brain stimulation and electroconvulsive shock)
80
Q

what is unique about planaria (freshwater flatworm)

A

undergoes cycles of de-growth and growth repeated indefinitely without impairing survival or fertility

81
Q

what percent of cells in planaria are stem cells (neoblasts)

82
Q

cell cannibalism

A

dead cells in planaria are phagocytosed and digested using all the nutrition

83
Q

transformation is common in what kind of species

A

non-mammalian species

e.g. newt limb following amputation –> differentiated muscle cells in the stump reenter the cell cycle, de-differentiate, and become embryonic cells and proliferate to form a lib bud similar to the embryo

Molecular & Cell Biology (10 decks)

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