Stem cells and differentiation

Question 1

What is an embryonic stem cell?

Answer 1

A cell of the inner cell mass of a blastocyst (3-5 day old embryo) - these cells give rise to the entire body

Question 2

Define a stem cell (Think of the three characteristics that separate every type of stem cell from a normal cell)

Answer 2

1. They are non-differentiated
2. They can divide and self-renew for long periods
3. Can be induced, under certain physiological/experimental conditions, to differentiate and thus specialise

Question 3

What is an adult or somatic stem cell?

Answer 3

Discrete stem cell populations located in tissues that require some form of continual repair/replacement, such as the GI tract, bone marrow, skin etc.
In almost all cases, their potency is limited to differentiation to the specialised cell types found in the tissues in which they are located

Question 4

What are induced pluripotent stem cells?

Answer 4

Genetically reprogrammed specialised adult cells - the reprogramming induces pluripotency
Viral transfection with a minimum of four transcription factors will induce pluripotency in a skin fibroblasts.

Question 5

What type of growth is typical of permanent tissues?
What type of growth is typical of renewing tissues?
Give examples for both

Answer 5

Hypertrophy, such as in skeletal muscle - this is simply an increase in cell volume
Hyperplasia, such as in skin or bone marrow - this is an increase in cell number (cell division occurs/proliferation) and thus a subsequent growth in tissue volume

Question 6

What is the term used to describe:
1 - a complete failure in cell/tissue growth and proliferation to occur
2 - a partial failure in cell/tissue growth and proliferation to occur

Give examples of each

Answer 6

1 - agenesis (Potter’s syndrome, leading to renal agenesis)
2 - hypoplasia (Klinefelter’s syndrome or XXY, leading to smaller testes; Turner’s syndrome or X, leading to small ovaries

Question 7

What are the causes of local atrophy?

Answer 7

Disuse (immobilised limb after trauma)
Ischaemia (blood supply cut off, no nutrients reaching tissue)
Neuropathy (nerve supply to tissue disrupted)
Idiopathic (no known cause of atrophy, like in Parkinson’s)

Question 8

What are the causes of general atrophy?

Answer 8

Starvation (lack of nutrients supplying tissues)
Malignant disease, this cause is also known as Cachexia or wasting syndrome - main characteristic of this syndrome is the wasting of muscle, and weight cannot be put back on even when caloric intake is increased