Haemopoiesis

Question 1

What is haemopoiesis?

Answer 1

The formation of blood cellular components.

Question 2

What are the precursors of haematopoietic stem cells? Where are they derived from and where do they migrate to?

Answer 2

Haemangioblasts

Aortic/Gonadal/Mesonephros region of mesoderm → Yolk sac, liver and bone

Question 3

What is the common precursor cell of all blood cells? And what drives them to differentiate?

Answer 3

Pluripotent Haemopoietic Stem cells

Stem cells which reside in bone marrow/other haemopoietic tissues

They proliferate/self renew - keep levels constant in tissues

Differentiate into any blood cell, driven by growth factors

Question 4

What do Lymphoid Progenitor (multipotent) cells differentiate into?

Answer 4

B lymphocytes, T lymphocytes, NK cells

Those responsible for producing T cells migrate to Thymus

Those responsible for producing B and NK cells stay in bone marrow

Question 5

What do myeloid progenitor cells differentiate into?

Answer 5

RBCs, platelets, monocytes/macrophages

Neutrophils, Basophils, Eosinophils

Remain in bone marrow

Question 6

What two growth factors act on haematopoietic stem cells and what effect do they have?

Answer 6

Stem cell factor - ↑Stem cell reproduction

IL-3 - ↑Myeloid progenitor cell production

Question 7

What growth factor acts on the Early Multipotential Cells (Myeloid progenitor, lymphoid progenitor cells)? and what effect does it have?

Answer 7

Granulocyte-Monocyte Colony Stimulating Factor -

G-MCSF

Stimulates production of monocytes and granulocytes from myeloid progenitors

Question 8

What growth factors act on the late/committed progenitor cells and what are their effects?

Answer 8

EPO - Produced by kidneys in response to ↓pO₂ → Accelerate production of RBCs

TPO - produced by liver and kidneys →

Accelerate production of Megakaryocytes → Platelets

G-CSF - Accelerates production and maturation of Neutrophils + Inhibits neutrophil apoptosis

Question 9

how do cells leave the bone marrow?

Answer 9

They must express the correct receptors, signalling their maturity

Pathology can occur when cells leave the marrow early, or do not leave when they should

Question 10

How long do erythrocytes spend in blood? How many are produced/second?

Answer 10

120 days

2-3 million/second

Question 11

What are reticulocytes? Why is their presence in anaemia significant?

Answer 11

Immature RBCs with nucelus still intact

Released into blood when bone marrow working hard

Presence in anaemia → marrow is working, therefore anaemia result of blood loss

Question 12

What are megakaryocytes?

Answer 12

Large platelet precursors → produce hundreds of inidividual platelets

Spend first 2 days in spleen, and 8-10 days in blood

Question 13

What are monocytes?

Answer 13

Spend first 3 days in marrow, then 3 days in peripheral blood, until differentiated

Differentiate into macrophages when migrated into tissues - live up to 80 days

Question 14

What is the life cycle of neutrophils?

Answer 14

Take 12 days to produce, spend 〜12 hours in circulation

Reservoir - marrow hold huge reservoir of neutrophils (30x blood) which can be released when required

Question 15

In the foetus, where does haemopoiesis take place?

Answer 15

Yolk sac - until 3 months

Liver and Spleen - 3-6 months

Bone marrow - 6+ months

Question 16

In children, where does haematopoiesis take place?

Answer 16

Bone marrow

Long bones and central bones initially important, less so as children grow

Question 17

In adults where does haemopoiesis take place?

Answer 17

Bone Marrow of Ribs, Sternum, Vertebrae and Pelvis (25+ yo)

Occasionally proximal ends of long bones too

Long bones, spleen and liver may resume function in ↑demand (chronic haemolytic anaemias) or leukaemia

Question 18

What is used to examine bone marrow architecture?

Answer 18

Bone marrow biopsy via Trephine - small, 1-2mm bore which collects core of bone marrow

Can show hypocellularity - large fat spaces, few haemopoietic cells

or hypercellularity