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Question 1

What does hematopoiesis refer to?

Answer 1

The process of formation, development, and differentiation of the formed elements of blood.

Question 2

From what cells does hematopoiesis originate?

Answer 2

Hematopoietic stem cells (HSCs).

Question 3

What are the key characteristics of hematopoietic stem cells (HSCs)?

Answer 3

• Ability to self-renew
• Differentiate into all mature blood cell lineages
• Rescue lethally irradiated hosts.

Question 4

What is the frequency of hematopoietic stem cells in bone marrow?

Answer 4

1 stem cell per 10,000 to 100,000 bone marrow cells.

Question 5

Under steady state, what is the state of HSCs?

Answer 5

Quiescent (noncycling).

Question 6

What triggers extensive proliferation of HSCs?

Answer 6

Hematopoietic stress (e.g., infections, acute bleeding, or chemotherapy).

Question 7

What can result from deregulation of self-renewal and differentiation processes?

Answer 7

Myeloproliferative diseases (e.g., acute myeloid leukemia) or bone marrow failure syndromes (e.g., aplastic anemia).

Question 8

What is primitive hematopoiesis and when does it occur?

Answer 8

Occurs in the yolk sac during 0–2 months of embryonic development, consisting primarily of large nucleated erythroid cells.

Question 9

When does definitive hematopoiesis take place?

Answer 9

In the aortic-gonad-mesonephros (AGM) region of the embryo.

Question 10

What is the origin of HSCs in definitive hematopoiesis?

Answer 10

May be derived from specialized endothelial cells in the dorsal aorta.

Question 11

What is the role of the AGM region?

Answer 11

Contains the dorsal aorta and is where definitive hematopoietic progenitors expand.

Question 12

What is stem cell plasticity?

Answer 12

The ability of adult tissue-specific stem cells to switch to new identities.

Question 13

Where does medullary hematopoiesis occur?

Answer 13

In the Bone Marrow within the ‘Red Marrow’.

Question 14

What is extramedullary hematopoiesis?

Answer 14

Occurs in organs other than the bone marrow (e.g., liver, spleen).

Question 15

What are the characteristics of stem cells?

Answer 15

• Self-maintenance
• Ability to produce multiple, varied offspring.

Question 16

What are the two essential attributes of true HSC populations?

Answer 16

• Immortality (self-renewal potential)
• Undifferentiated state while giving rise to multi-lineage differentiation.

Question 17

What are the possible fates of HSCs at the single cell level?

Answer 17

• Self-renewal
• Differentiation
• Migration
• Apoptosis.

Question 18

What types of stem cells exist?

Answer 18

• Totipotent stem cells
• Pluripotent stem cells
• Multipotent stem cells.

Question 19

What defines a multipotent stem cell?

Answer 19

Capable of giving rise to multiple mature cell types, but only those of a particular tissue.

Question 20

What is the bone marrow microenvironment?

Answer 20

Provides a suitable environment for stem cell growth and development.

Question 21

What is self-renewal in hematopoietic stem cells?

Answer 21

The ability to give rise to identical daughter HSCs without differentiation.

Question 22

What is the difference between pluripotent and multipotent stem cells?

Answer 22

• Pluripotent: can become any type of cell except extra-embryonic tissues
• Multipotent: can become multiple types within a specific tissue.

Question 23

What is the role of common lymphoid progenitors (CLP)?

Answer 23

They further divide into lymphocyte progenitors capable of generating T, B, and natural killer (NK) cells.

Question 24

What do common myeloid progenitors (CMP) give rise to?

Answer 24

• Granulocyte-monocyte progenitor cells
• Megakaryocyte-erythrocyte progenitor cells.

Question 25

What is the role of transcription factors in hematopoiesis?

Answer 25

Regulate survival of stem cells and differentiation along major cell lineages.

Question 26

What is commitment in hematopoiesis?

Answer 26

Cells become limited to hematopoietic progress in a single cell lineage.

Question 27

What occurs during the maturation of hematopoietic cells?

Answer 27

Cells continue to mature and develop characteristic features making them fit for special functions.

Question 28

What is the regulatory process during hematopoiesis?

Answer 28

Begins with stem cell division where one cell replaces the stem cell (self-renewal) and the other is committed to differentiation.

Question 29

What are the two fates of progenitor cells?

Answer 29

Self-renewal and differentiation

Question 30

What is the role of transcription factors in progenitor cells?

Answer 30

Regulate survival and differentiation along major cell lineages

Question 31

What influences the selection of cell lineage for differentiation?

Answer 31

Chance and external signals received by progenitor cells

Question 32

What are haemopoietic growth factors?

Answer 32

Glycoprotein hormones that regulate proliferation and differentiation of haemopoietic progenitor cells

Question 33

What is the major source of growth factors in haemopoiesis?

Answer 33

Stromal cells, except for Erythropoietin and Thrombopoietin

Question 34

What is crucial for successful haemopoiesis?

Answer 34

Communication between cells in the bone marrow microenvironment

Question 35

What are cytokine growth factors?

Answer 35

Hormone-like molecules that pass messages between cells

Question 36

What is the function of stem-cell factor (SCF)?

Answer 36

Ligand for the c-kit receptor that moves the cell along the cell-cycling pathway

Question 37

What does IL-3 act on?

Answer 37

Cells from the stem cell level down to and including the CFUs

Question 38

What are interleukins?

Answer 38

Molecules released by leucocytes that act on other leucocytes and non-leucocytes

Question 39

What are colony-stimulating factors (CSFs)?

Answer 39

Regulatory factors dominating the regulation of haemopoiesis

Question 40

What are the general characteristics of myeloid and lymphoid growth factors?

Answer 40

Glycoproteins that act at low concentrations, produced by many cell types, affect multiple lineages

Question 41

What are the multiple functions of growth factors?

Answer 41

* Proliferation * Differentiation * Maturation * Functional activation * Prevention of apoptosis

Question 42

What is apoptosis?

Answer 42

Programmed cell death regulated by intracellular proteins

Question 43

What are the characteristics of apoptosis?

Answer 43

* Cell shrinkage * Condensation of nuclear chromatin * Nuclear fragmentation and DNA cleavage

Question 44

What triggers the apoptosis process?

Answer 44

Failure to receive growth factor signals or survival factors

Question 45

How many cells does an adult human lose approximately per day?

Answer 45

Approximately 10^11 cells

Question 46

What tissues account for the majority of physiologic cell death in adults?

Answer 46

Skin, intestinal, and hematopoietic tissues

Question 47

What happens to neutrophils recruited to sites of inflammation?

Answer 47

They undergo apoptosis concurrent with removal of the inflammatory stimulus

Question 48

What cytokines do apoptotic neutrophils secrete?

Answer 48

* IL-10 * TGF-β

Question 49

What is a hallmark of apoptosis regarding phospholipid distribution?

Answer 49

Loss of normal asymmetry with accumulation of phosphatidylserine in the outer leaflet